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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 677-681 
    ISSN: 1572-8854
    Keywords: Anthraquinone ; crystal structure ; intramolecular hindrance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the monoclinic space group, P21/c;a=12.938(1),b=11.041(1),c=19.285(2) Å, β=104.314(8)°,Z=4. Refinement based on 1660 unique observed reflections converged toR=0.054. The anthraquinone moiety is distorted due to intramolecular steric hindrance from the tosylate groups.
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  • 2
    ISSN: 1572-8854
    Keywords: Organoiron complex ; dinuclear complex ; crystal structure ; phosphonium ylid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric monoclinic space group P21/n withZ=4. The cation consists of two (η5-C5h5)Fe(CO) units which are linked via a metal-metal bond (Fe(1)−Fe(2)=2.530(1) Å), a bridging carbonyl ligand (Fe(1)−C(4)=1.912(8) Å. Fe(2)−C(4)=1.940(9) Å) and a bridging phosphonium ylid ligand (Fe(1)−C(1)=1.991(6) Å, Fe(2)−C(1)=1.985(6) Å and C(1)−P(1)=1.781(6) Å).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 747-752 
    ISSN: 1572-8854
    Keywords: Phosphine oxide ; quaternary ammonium ; water-soluble phosphine ; crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric triclinic space group $$P\bar 1$$ withZ=4. The crystallographic asymmetric unit contains two independent cations; interatomic distances within these include P=O=1.47(1) and 1.47(1) Å, P−C6H5=1.78(2)–1.81(1)Å and P−CH2CH2NMe3 +=1.80(1) and 1.81(1) Å. The phosphine oxide moiety is involved in intermolecular hydrogen bonding ()...H−C, with O...H≥2.42Å) and the iodide is involved in I...H−C contacts with I...H≥3.10Å.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 185-189 
    ISSN: 1572-8854
    Keywords: Solid-solid reaction ; inclusion compound ; p-toluidine ; cholic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Cholic acid undergoes solid-solid reactions with some aromatic molecules to form inclusion compounds. Simple shaking of a mixture of powdered cholic acid andp-toluidine results in formation of the 1∶1 (host:guest) inclusion compound which has the same structure as that formed by conventional crystallization methods: monoclinic space groupP21 witha=13.577(4),b=8.078(2),c=14.182(6) Å, β=114.42(3)°,Z=2 andR 1=0.061 for 2680 unique reflections.
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  • 5
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; disordered structure ; crystal structure ; solvate ; triphenylphosphine ; bipyridyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru{4,4′-(t-Bu)2bpy}2(PPh3)Cl+][ClO 4 − ·0.5(toluene)·0.5(MeCN), where 4,4′-(t-Bu)2bpy=4,4′-di(t-butyl)-2,2′-bipyridyl crystallizes with an ordered racemic mixture of the chiral cations in the centrosymmetric triclinic space group $$P\bar 1$$ (No. 2). The structure was refined toR=4.42% for those 6426 reflections with 20=5–50o and |F o|〉6σ(F). Ruthenium ligand distances are Ru−Cl=2.423(2)Å, Ru−PPh3=2.346(2)Å and Ru−N=2.056(4)–2.098(4)Å. Both the Ru(II)-containing cation and the perchlorate anion are ordered, but the toluene and acetonitrile exhibit an interesting type of scrambled disorder about the inversion center atx=1,y=1/2,z=0.
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  • 6
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium-rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The monocarbonyl complex Re2Cl4(µ-dppm)2(CO) reacts with xylyl isocyanide in acetonitrile to afford the bioctahedral complex (CO)Cl2Re(µ-dppm)2 ReCl2(CNxyl), 2b. This is a different structural isomer from the edge-sharing bioctahedral complex Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNxyl) or this same stoichiometry which A formed when acetone is be reaction solvent. The complex2b reacts with a further equivalent of xylNC in the presence of TlO3SCF3 in dichloromethane to form a red complex of composition [Re2Cl3(µ-dppm)2 (CO)(CNxyl)2]O3SCF3. 3, which has the open bioctahedral structure [(xylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3. This is a third isomeric form of this dirhenium cation: the previously isolated green and yellow forms have edge-sharing bioctahedral structures. Crystal data for3 at 295 K: orthorhombic space group Pbca (No. 61) witha=22.654(5) Å,b=22.717(4) Å,c=27.324(4) A,V= 14061(7) Å3, andZ = 8. The structure was refined to R = 0.059 (R, = 0.134 ) for 14164 data. The Re-Re distance is 2.3833(8) Å.
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  • 7
    ISSN: 1572-8854
    Keywords: Ruthenium(II) ; bipyridyl ; phenyldi(o-tolyl)phosphine ; solvate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2{PPh(o-tolyl)2}Cl+][ClO4 −] crystallized from a solution in dichloromethane as the dichloromethane-water solvate. The structure was refined toR=4.5% for those 2433 reflections with |F o|〉6σ(|F o|). The octahedral Ru(II) cation is associated with metal-ligand distances as follows: Ru−Cl=2.434(3)Å, Ru-PPh(o-tol)2=2.382(2)Å, and Ru−N=2.037(7)–2.088(7)Å. The structure is stabilized by a hydrogen-bonded CH2Cl2...ClO4 −...H2O channel which incorporates adventitious water of crystallization.
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  • 8
    ISSN: 1572-8854
    Keywords: Silver ; stearate ; triphenylphosphine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C6H5)3P)2Ag(O2C(CH2)16CH3)], has been determined by single crystal X-ray analysis: the space group is PT witha=12.021(4),b=13.916(5)1,c=14.678(5) Å, α=95.952(5), β=101.249(6), γ=93.259(5)°,V=2388(2) Å3, andD calc=1.293 g/cm3 forZ=2. The silver is four coordinate: the carboxylate symmetrically chelates the silver while the triphenylphosphine ligands occupy the third and fourth coordination sites. The strong bonding nature of the phosphine ligands, as indicated by the Ag−P bond lengths, 2.446(3) and 2.424(3) Å, dominates the coordination sphere of the silver and forces the initial carboxylate ligand to rearrange from bridging to chelating resulting in weaker Ag−O bonds, as indicated by the extended Ag−O bond lengths, 2.399(8) and 2.449(8) Å. Unlike the free acid, the long hydrocarbon chain is not linear, and exhibits disorder in the lattice. The structure of the title complex explains the dramatic shift in solubility properties compared to the starting phosphine free silver carboxylate.
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  • 9
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; organoruthenium compound ; bis(1,2-diphenylphosphino)ethane ligand ; ruthenium-nitro complex ; crystal structure ; cyclopentadienyl derivative ; methanol solvate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title complex crystallizes in the centrosymmetric monoclinic space group C2/c (No. 15) withZ=8. The structure was refined toR=4.49% for those 2745 independent reflections with 2θ=5–50o and |F σ|〉6σ(F). Ruthenium-ligand distances are as follows: Ru-P=2.284(2) and 2.286(2) Å, Ru-NO2=2.049(6) Å and Ru-C(Cp)=2.210(10)-2.246(9) Å. Bond lengths within the nitro ligand are N(1)-O(1)=1.226(10) Å and N(1)-O(2)=1.244(10) Å. The methanol of solvation is ordered but is subject to large thermal vibrational motions.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 461-465 
    ISSN: 1572-8854
    Keywords: Molecular dynamics ; crystal structure ; TOT clathrate ; thiophene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Tri-o-thymotide (TOT) forms a cage-type clathrate with the thiophene guest molecule in a host:guest ratio of 2∶1. This clathrate crystallizes in the trigonal system (space groupP3121). The unit cell, of dimensionsa=b=13.585(4),c=29.914(12)Å, contains 6 TOT and one thiophene molecule. The crystal structure, established by direct methods (R=0.053), indicates that the host cavity has an oblate-ellipsoid shape with a crystallographic twofold axis parallel to the largest dimension of the cage. The guest molecule within the cavity is disordered. Molecular dynamics simulations have been performed and indicate that the guest molecules have hindered molecular freedom around the shortest ellipsoid axis of the cavity, and may produce a dynamic disorder in the cage of the TOT clathrate.
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  • 11
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; terpyridine ; ruthenium-nitro complex ; crystal structure ; disordered ligands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPr3) 2 + ][ClO 4 − ]crystallizes in the centrosymmetric orthorhombic space group Pnma withZ=4. Both the ruthenium(II) cation and the perchlorate ligand lie about crystallographic mirror planes. The nitro ligand is not coplanar with the Ru(trpy) moiety and suffers from two fold disorder about its Ru−N bond such that the two sets of oxygen atoms have symmetry-related sites above or below the crystallographic mirror plane. The n-propyl groups within the PPr3 ligands suffer from disorder of their C(α) and C(β) atoms but share common C(γ) sites. Ruthenium-ligand distances are: Ru−PPr3=2.398(2)Å, Ru−NO2=2.053(7) Å, Ru−N(trpy, outer)=2.078(6) and 2.092(6) Å and Ru−N(trpy, central) =1.965(6) Å.
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  • 12
    ISSN: 1572-8854
    Keywords: Chromium ; carbonyl ; arene ; acetal ; crystal structure ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structures of the (benzene dialkylacetal)tricarbonyl chromium complexes [η6-C6H5-CH(OR)2]Cr(CO)6 (R=Me,1; Et,2), are reported. The compounds were examined as part of a study of the conformations of the tripodal tricarbonylchromium group. For [η6-C6H5-CH(OMe)2]Cr(CO)3,1, monoclinic,P21/c (# 14),a=15.235(1) Å,b=6.5304(5) Å,c=12.702 Å, β=103.197(1)o,Z=4. For [η6-C6H5-CH(OEt)2]Cr(CO)3,2, monoclinic,P21/c (# 14),a=9.859(3) Å,b=10.547(3) Å,c=15.138(3) Å, β=108.42(2)o,Z=4. The data show that the molecules adopt the expected “three-legged piano stool” structure. The carbonyl ligands in1 adopt an eclipsed arrangement with respect to the arene ring and its substituent, while those in2 are staggered. These conformations are consistent with the notion that the acetal substituent behaves largely as an electroneutral group, or at most as a weak electronic acceptor.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 389-392 
    ISSN: 1572-8854
    Keywords: p-Methoxyphenyltelluro ; x-ray diffraction ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract C23H18TeO,M r=437.97, $$P\bar 1$$ ,a=9.940(2),b=13.664(3),c=7.895(2) Å, α=80.60(1), β=69.71(2), γ=75.95(1)°,V=972.0(4) Å3,Z=2,R=0.041 for 2668 observed reflections. The Te−C bond distances are 2.109(5)Å and the C−Te−C angle is 96.0(2)°. The phenyl rings are planar to within experimental accuracy, making dihedral angles of 64.6(2), 65.3(2) and 31.1(3)°.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 403-406 
    ISSN: 1572-8854
    Keywords: Cyclotrithiazene ; arylaminophospine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound (C6H5)2(OC4H8N)P=N−S3N3 crystallizes in the space group $$P\bar 1$$ with unit cell parametersa=9.3900(2),b=9.4747(1),c=11.3850(3) Å, α=95.73(4), β=96.85(6), γ=104.26(2)o, and Z=2. The tricoordinated sulfur of the cyclotrithiazene ring deviates from the mean plane of other skeletal atoms by 0.683(4) Å. The angle at this atom is the smallest in the ring and is enclosed by the longest S−N bonds observed in the ring.
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  • 15
    ISSN: 1572-8854
    Keywords: Copper(II) complex ; crystal structure ; coordination polymer ; betaine ; dicarboxylate ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three polymeric copper(II) complexes of a flexible double betaine, namely, [{Cu(L)Cl2(H2O)} n ]·2 n H2O (1), [{Cu(L)Br2(H2O)} n ]·2nH2O (2), and [{Cu(L)(H2O)4} n ](ClO4)2n ·2nH2O (3) [L=−O2CCH(Me3N+)CH2CH2CH(Me3N+CO2], have been prepared and characterized by singlecrystal X-ray analysis. Isomorphous complexes (1) and (2) crystallize in space groupC2/c (No. 15) witha=17.725(3),b=5.958(2),c=19.077(3) Å, β=110.70(1)o,V=1881.4(4) Å3, Z=4 anda=18.268(4),b=5.948(3),c=19.166(5) Å, β=109.08(2)o,V=1964.7(9) Å3, Z=4, respectively. Complex (3) belongs to space groupPĪ (No. 2) witha=6.203(1),b=9.293(2),c=12.035(2) Å, α=86.56(2), β=87.33(3), γ=71.23(2)o,V=655.4(2) Å3 and Z=1. The crystal structure of (1) and (2) features an infinite zigzag chain composed of an alternate arrangement of metal atoms and double betaines ligands, with each Cu(II) atom in a distorted CuX2O3 [X-Cl, Br] square-pyramidal geometry, and hydrogen bonding between adjacent chains leads to a layer structure concentrated the (200) family of planes. Complex (3) exhibits a layer structure corresponding to the (001) family of planes, in which neighboring chains constructed from the metal atoms and the double betaine ligands are cross-linked by hydrogen bonding between the aqua ligands. The Cu(II) atom is coordinated in a CuO6 octahedral geometry with Jahn-Teller distortion.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 503-508 
    ISSN: 1572-8854
    Keywords: Tin(IV) sodium(I) complex ; ethylenediaminetetraacetic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract NaSn(OH)(edta)(H2O) is monoclinic, space groupP21/c, witha=9.747(3)Å,b=9.121(3)Å,c=16.430(6)Å, β=98.69(4)°, Å3, andZ=4. The coordination environment of Sn(IV) is a capped octahedron. Sn−O distances range from 1.990(6)Å to 2.351(7)Å. Na(I) is five coordinated to three different edta molecules. Na−O distances range from 2.283(9)Å to 2.414(7)Å. The edta ligand presents the E, G/R conformation. The crystal structure is composed of sheets parallel to (001): inside a sheet Sn(OH)(edta) molecules are connected to each other by the Na(I) interactions.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 515-518 
    ISSN: 1572-8854
    Keywords: Antiarrhythmic agent ; crystal structure ; absolute configuration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space groupP212121, withZ=4,a=4.770(1)Å,b=6.620(1)Å,c=37.550(7)Å,R=0.04. The most important factors affecting conformation of the molecules are: the protonation state of the N(9) atom andortho-substitution of the benzene ring in the acetanilide system. Protonation promotes an extended form of the molecule and 2,6-substitution forces a twist of at least 60° between the benzene ring and amide group planes. The resulting separation of lipophilic (xylidine) and amine groups, being two important pharmacophores, equals about 5Å in tocainide and all other structures comprising the amino-2,6-dimethylacetanilide system.
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 553-557 
    ISSN: 1572-8854
    Keywords: Silver(I) complex ; synthesis ; crystal structure ; spectroscopic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The reaction of [Ph3PAgI]4 with sodium phenylacetate in MeOH and CH2Cl2 at room temperature gave rise to a binuclear silver complex with triphenylphosphine and phenylacetate mixed ligands, [Ph3PAg(O2CCH2Ph)]2. The crystal and molecular structure of the complex has been determined by single crystal X-ray diffraction analysis. The space group is $$P\bar 1$$ witha=9.198(2),b=9.516(2),c=13.842(3) Å, α=102.00(3), β=108.34(3), γ=93.58(3)°,Z=1, andDc=1.506 g cm−3. The silver atoms are each coordinated by one phosphorus atom from triphenylphosphine and two oxygen atoms from the carboxylate groups in a T-shape. The complex is further characterized by its IR,1H, and31P NMR spectra.
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  • 19
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; bipyridyl ; crystal structure ; disorder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2(PPr3)Cl+][ClO 4 − ] · 0.5 (toluene) crystallizes as a racemate in the monoclinic space group P21/n. Both the PPr3 ligand and the toluene of crystallization are subject to disorder. Ruthenium—ligand distances are: Ru−PPr3=2.348(2) Å, Ru−Cl=2.426(2) Å and Ru−N(bpy)=2.035(6)–2.112(5) Å.
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  • 20
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; terpyridine ; triphenylphosphine ; ruthenium-nitro complex ; crystal structure ; pseudo-lattice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPh3) 2 + ][PF 6 − ] crystallizes in the centrosymmetric monoclinic space groupP21/n withZ=4; the ruthenium atom lies close toy=1/4 and all data withh+l=2n+1 are systematically weak. The trpy ligand is not strictly planar, but has a “dish-like” geometry. The nitro ligand is rotated from the plane of the Ru(trpy) moiety, the N3Ru/NO2 interplanar angle being 32.5o. Ruthenium-ligand distances are: Ru−PPh3=2.418(4) Å and 2.429(4) Å, Ru−NO2=2.063(12) Å, Ru−N(trpy, outer)=2.100(12) Å and 2.116(12) Å and Ru−N(trpy, central)=2.004(11) Å.
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  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 661-665 
    ISSN: 1572-8854
    Keywords: N,N′-bis(2-hydroxyphenyl)butanediamide ; crystal structure ; hydrolysis product
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure of N,N′-bis(2-hydroxyphenyl)butanediamide has been determined. The molecule consists of two 2-hydroxyphenyl moieties which are attached (at the 2 position) to the two nitrogens of the butanediamide. The compound C16H16N2O4 crystallizes in the monoclinic space group P21/c witha=5.576(1),b=4.8853(6),c=25.397(6) Å and β=90.58(1)°.
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  • 22
    ISSN: 1572-8854
    Keywords: Organotin ; crystal structure ; flavone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 1∶1 adduct of chlorotriphenyltin with 2′,6′-dimethoxyflavone, (C35H29O4ClSn)Mr=667.78, crystallizes in the triclinic space groupP1 with the following data:a-9.094(2),b=12.369(3),c=14.674(3) Å, α=74.78(2), β=77.00(2), γ=73.06(3)°,V=1503.8(4) Å3,Z=2, Mo-Kα, μ=9, 8 cm−1,Dc=1.475 g cm−3, F(000)=676,T=293K. The structure was solved by direct-methods and has been refined to a finalR value (l〉3σ(I)) of 0.0301. The flavone coordinates to the tin atom through the carbonyl oxygen atom. The metal center exhibits a trigonal bipyramidal configuration with the three phenyl groups in equatorial positions.
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  • 23
    ISSN: 1572-8854
    Keywords: Betaine ; 4-dimethylaminopyridinioacetate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystalline dihydrate and hydrochloride trihydrate of a new betaine, namely, L·2H2O (1) and [L2H]Cl·3H2O(2) (L=p-Me2NC5H4N+CH2CO2), have been synthesized and characterized by X-ray crystallography. Molecule L in compound1 [space groupPbcn, witha=15.732(3),b=7.894(2),c=18.304(4) Å, andZ=8] possesses approximateC s symmetry. The formation of hydrogen bonds by water molecules bridging neighboring carboxy oxygen atoms leads to an infinite two-dimensional network composed of a packing of two different kinds of 12-membered rings. In compound2 [space group PT witha=7.341(2),b=9.543(2),c=17.010(4) Å, α=82.43(2)°, δ=80.34(2)°, λ=74.05(2)°, andZ=2], the carboxylate groups of a pair of betaine molecules are bridged by a proton to form a dimeric cation L2H+ with a very strong asymmetric hydrogen bond of length 2.464(7) Å. The crystal structure features a hydrogen-bonded corrugated ribbon comprising an alternate arrangement of edge-sharing centrosymmetric (H2O)4(Cl−)2 and (H2O)4 rings running parallel to thea axis.
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  • 24
    ISSN: 1572-8854
    Keywords: Bidentate ligand ; crystal structure ; pyrazolyl group ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound lies on a site of C2 symmetry, with the two planar pyrazolyl moieties oriented at 86.1° to one another. The hydrogen atoms were located and refined.
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  • 25
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    Journal of chemical crystallography 26 (1996), S. 219-222 
    ISSN: 1572-8854
    Keywords: Steroid ; organometallic ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 3α-Triphenylstannylcholest-5-ene (1) has been synthesised and its molecular structure has been determined by single crystal X-ray diffraction. Refinement in the triclinic space groupP1 witha=7.805(6),b=7.862(5),c=32.351(10)Å, α=90.87(8), β=94.77(8) and γ=101.15(4)o converged atR=0.063. One of the two crystallographically independent molecules in the unit cell has a patially disordered side chain. The bond lengths and valency angles about tin indicate some steric hindrance due to the proximity of one of the phenyl rings with the B ring of the steroid nucleus.
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  • 26
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    Journal of chemical crystallography 26 (1996), S. 841-846 
    ISSN: 1572-8854
    Keywords: Cu(II) resorcylidene aminoguanidine ; synthesis ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The tridentate Schiff base, β-resorcylidene aminoguanidine (RAG)1 was synthesized from 2,4-dihydroxybenzaldehyde and aminoguanidine and complexed with copper(II) to form a copper(II)-β-resorcylidene aminoguanidine (Cu-RAG)2 complex. X-ray diffraction analysis of compound2 (orthorhombic, Pnma,a=11.674(1);b=6.7198(7);c=17.836(2) Å) revealed a square-planar copper(II) cation with a tridentate·ligand bound through two nitrogen atoms (N1 and N3) of the aminoguanidine moiety and an oxygen (O1) of the monodeprotonated dihydroxybenzaldehyde function. The remaining coordination site was occupied by chloride and the structure was rigidly planar as demanded by the restrictions of the crystallographic space group. The unit cell contents exhibited an extended sheet-like structure constructed via hydrogen bonds both intermolecularly and involving two water molecules (O3 and O4) also restricted by the same mirror symmetry. The remaining water (O5) provided for interlayer hydrogen bonding.
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  • 27
    ISSN: 1572-8854
    Keywords: Pyrazolyl group ; crystal structure ; bidentate ligand ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound consists of two planar pyrazolyl fragments oriented at 73.0° to each other and linked to a common carbon atom. All hydrogen atoms were located unambiguously and their positions were refined.
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  • 28
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; bipyridyl ; diphenyl(o-tolyl)phosphine ; dichloromethane solvate ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2 {PPh2(o-tol)}Cl][ClO4] crystallizes from dichloromethane as the sesqui-dichloromethane solvate. The complex crystallizes in the monoclinic space group P21/n with Z=4. The structure was refined toR=5.50% for those 2552 independent reflections with |F 0|〉6σ(|F 0|) The octahedral Ru(II) cation is associated with the following bond lengths: Ru-PPh2(o-tol)=2.360(3)Å. Ru−Cl=2.433(2)Å and Ru−N(bpy)=2.041(8)–2.095(8)Å. Both the perchlorate anion and the dichloromethane molecules of solvation exhibit large amplitudes of vibration. One dichloromethane molecule lies in a general position, the other lies about an inversion center and suffers from disorder.
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  • 29
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    Journal of chemical crystallography 26 (1996), S. 615-619 
    ISSN: 1572-8854
    Keywords: Disordered trifluoromethyl group ; quinoline ; crystal structure ; AM1 calculation ; mefloquine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallized in space groupPna21 with lattice constantsa=13.406(1),b=18.799 (4), andc=4.785(1). The molecule is essentially flat with only fluorine atoms, methylene hydrogen atoms, and the hydroxyl hydrogen atom out of the plane of the quinoline ring. Only one of the trifluoromethyl groups of the title compound is disordered following a pattern observed in other crystal structures. Quantum chemical calculations at the AM1 level are consistent with this phenomenon. Although the carbon atom of the fixed trifluoromethyl group is further from the quinoline nitrogen atom than the carbon atom of the disordered trifluoromethyl group, the fluorine atoms of the fixed trifluoromethyl group more closely approach the quinoline nitrogen atom by 0.3 Å if the C(8)−C(10) bond in the crystal structure is freely rotated.
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  • 30
    ISSN: 1572-8862
    Keywords: Niobium(III) ; edge-sharing bioctahedra ; di-p-tolylformamidinato ; thiomethoxide ; double-bond ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reaction of NaEt3BH with Nb2(μ-SMe2)3Cl6 results in the transfer of a hydride ion to dimethylthioether with concomitant production of methane. Further reaction with potassium di-p-tolylformamidinate, KDTolF, yields Nb2(μ-SMe)2(μ-DTolF)2η2-DTolF:)2.2 toluene, 1. In the latter, two thiomethoxide ions and two DTolF groups bridge the trivalent niobium atoms. Each of the other two DTolF groups chelate a metal atom to give the molecule an edge-sharing bioctahedral structure, The niobium-niobium distance of 2.655(2) A is consistent with the presence of a double bond between the metal atoms.
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  • 31
    ISSN: 1572-9001
    Keywords: Cobalt complexes ; potassium squarate ; crystal structure ; molecular structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Compound (I), idealized as Br4Co3O14N8C16H41 (see text), crystallizes in the triclinic space groupP¯ 1 (No. 2) with cell constants ofa=7.4470(7),b=7.9648(4),c=15.2223(8),α=96.338(4)ℴΒ=93.504(6)ℴ,γ=112.894(6)ℴ,V=821.328 å3, and d(calc; MW=1065.97,z=1)=2.155 gm-cm−3. Data (3880 total reflections) were collected over the range 2ℴ ≤ 2θ ≤ 55ℴ and corrected for absorption (Μ=63.69 cm−1) using data from Psi scans. The unexpectedly isolated compound contains a [cis-Co(en)2Br(OH)]+ cation, while the anion contains a central Co(III) surrounded by two mondentate,trans-squarato ligands, twotrans-hydroxo, and two waters. The waters and hydroxy ligands were identified by determining, experimentally, the presence and positions of their respective hydrogens. Given the need for overall electroneutrality, one squarato ligand must be a dianion (Sq2−) and the other a monoanion (SqH−); however, since the ion bearing the squarato ligands sits at an inversion center, the hydrogen of the latter must be disordered. Refinement of the heavy atoms with anisotropic thermal parameters and fixed hydrogen positions (B's fixed at) led to the finalR(F) andR W(F) factors of 0.036 and 0.042, respectively. (I) was obtained during efforts to prepare [Co(en)2(squarate)]Br by the displacement of two chloro ligands from the coordination sphere of [cis-Co(en)2Cl2]Cl by K2 (squarate) followed by addition of NaBr. Compound (I) appears to be the first example of a coordination compound in which squarate2− and squarate H− anions are present as ligands to a transition metal ion. A search of the Cambridge file (to 1992) produced no known examples of Co(III) squarates. Thus, (I) appears to also be the first example of its kind.
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  • 32
    ISSN: 1572-9001
    Keywords: Protected tripeptide ; solution structure ; crystal structure ; X-ray analysis ; NMR analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The solid-state structure of Boc-Gly-Trp-Ala-OBut was determined by single-crystal X-ray diffraction analysis. The tripeptide gave crystals belonging to the orthorhombic systemP212121 and at 122.0(5) K:a=11.0663(12),b=14.107(2),c=17.275(2) Å,V=2697.0(5) Å3Z=4,R(F)=0.0259, andR w(F)=0.0695. The peptide adopts a type-Iβ-turn in the solid state with a single, rather weak, intramolecular hydrogen bond between the Boc-CO and Ala-NH groups (N⋯O 3.082(1) Å, 〈NH⋯O 167(1)°). The conformation of the Boc-Gly-Trp-Ala-OBut peptide has also been studied by1H NMR spectroscopy. The solvent and temperature dependencies of NH chemical shifts suggests that this hydrogen bond is broken and that all amide protons are solvent exposed in CDCl3 and (CD3)2SO.
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  • 33
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    Journal of thermal analysis and calorimetry 46 (1996), S. 719-731 
    ISSN: 1572-8943
    Keywords: aromatic polyimide fiber ; as-spun fiber ; crystallization ; crystal structure ; crystal unit cell ; draw ratio ; dry-jet wet spinning ; isotropic solution ; modulus ; self-elongation ; tensile strength ; thermal shrinkage stress ; thermal shrinkage strain ; thermomechnical analysis ; triclinic ; wide angle X-ray diffraction ; zone drawing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three aromatic polyimides based on 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride (BPDA) and three different diamines 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), 2,2′-dimethyl-4, 4′-diaminophenyl (DMB) or 3,3′-dimethylbenzidine (OTOL) have been synthesized. These polyimides are soluble in hotp-chlorophenol,m-cresol or other phenolic solvents. Fibers have been spun from isotropic solutions using a dry-jet wet spinning method. The as-spun fibers generally exhibit low tensile properties, and can be drawn at elevated temperatures (〉380° C) up to a draw ratio of 10 times. Remarkable increases in tensile strength and modulus are achieved after drawing and annealing. The crystal structures of highly drawn fibers were determinedvia wide angle X-ray diffraction (WAXD). The crystal unit cell lattices have been determined to be monoclinic for BPDA-PFMB and triclinic for both BPDA-DMB and BPDA-OTOL. Thermomechanical analysis (TMA) was used to measure thermal shrinkage stress and strain. A selfelongation has been found in the temperature region around 450°C. This phenomenon can be explained as resulting from the structural development in the fibers as evidencedvia WAXD observations.
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  • 34
    ISSN: 1572-9001
    Keywords: Betaine ; sodium perchlorate ; crystal structure ; polymeric framework
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three crystalline complexes of sodium perchlorate with different flexible double betaines [Na 2(L1)(ClO4)(H2O) n ](ClO4) n (1), [Na 3(L2)(ClO4)3(H2O)2 n ] (2), and [Na(L 3)(CH3OH)n]-(ClO4) n ·xnH2O (x=0.25) (3) [−O2CCH2N+Me2−(CH2) n -N+Me2CH2CO2 −,n=2 L1;n=3 L2;n=4 L3] have been synthesized and characterized by single-crystal X-ray structure analysis. Complex (1) comprises tetranuclear sodium units consolidated by betaine and aqua ligands, which are bridged by half of the ClO4 − anions to form layers matching the (200) planes, the remaining uncoordinated ClO4 − anions being accommodated between adjacent layers. Complex (2) possesses a double-layer polymeric structure with the sodium atoms bridged by ligand oxygen atoms to form columns running parallel to thea axis, which are interconnected by double-betaine ligands lying parallel to theac plane. All of the ClO4 − groups and water molecules are coordinated to the metal atoms. In complex (3) the chains composed of alternating eight-membered and four-membered metallocycles are cross-linked by the betaine ligands, which lie in the (020) and (01/1) families of planes, to yield a three-dimensional network. All of the ClO4 − groups and water molcules fill the resulting infinite channels running parallel to thea axis. Two unusual carboxylate coordination modes are identified, namelyμ 3-O andhapto-3-O plushapto-2-O′ in (1) and (2), respectively.
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  • 35
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    Russian chemical bulletin 45 (1996), S. 370-375 
    ISSN: 1573-9171
    Keywords: organic conductors ; bis(ethylenedithio)tetrathiafuIvalene ; mercury halides ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new organic semiconductor, (ET)8[Hg4C112] · 2C6H6, obtained in the ET+-HgCl 3 − -PhF system has been studied by X-ray structural analysis. Radical cations of bis(ethylenedithio)tctrathiafulvalene (ET) in the organic layer of the structure are packed in stacks ofa-type. The average angle between the planes of ET cations from adjacent stacks is 50.1°. The anionic layer is formed by four-charge centrosymmetric [Hg4Cl12]4− complexes and benzene solvate molecules. A comparative crystal-chemical study of the salts obtained by the reaction in the ET+-HgX 3 − -PhY system (where X = Cl, Br, and I; Y = F, Cl, and Br) made it possible to reveal a substantial effect of the sizes of the X and Y atoms on the composition of the salts and on the structural characteristics of the layers, which are responsible for the various conductivities of these salts.
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  • 36
    ISSN: 1573-9171
    Keywords: substituted sulfur-containing cyclopentadienes ; cyclopentadienyl zirconium complexes ; dynamic behavior ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Chelating sulfur-containing cyclopentadienyl ligand tetramethyl(2-methylthioethyl)cyclopentadiene (1), was synthesized for the first time. Its sodium (2a) and lithium (2b) derivatives were isolated in the crystalline state. Starting from compound1 some novel ZrIV complexes were prepared: [tetramethyl(2-methylthioethyl)cyclopentadienylltriclllorozirconium (3), bis[tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (4), and [pentamethylcyclopentadienyll [tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (5). The crystal structures of3 and5 were determined by X-ray diffraction analysis. The dynamic behavior of complex3 in various solvents was investigated by1H and13C N MR spectroscopy. The S→Zr coordination bond was shown to exist in complex3 both in the crystalline state and in solution. No coordination of this type was found in compounds4 and5.
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  • 37
    ISSN: 1573-9171
    Keywords: cyclopentadienes with oxygen-containing substituents ; cyclopentadienyl zirconium complexes ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Several novel zirconium(iv) complexes with the chelating oxygen-containing cyclopentadienyl ligand, tetramethyl(2-methoxyethyl)cyclopentadiene, have been synthesized. [η5:η1-Tetra-methyl(2-methyl)cyclopentadienyl]trichlorozirconium (2), bis[η5-tetramethyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (3), [η5-pentamethylcyclopentadienyl][η5-tetra-methyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (4), and [η5-tetra-methyl(2-methylthioethyl)cyclopentadienyl][η5-tetramethyl(2-methoxyethyl)-cyclopentadienyl]dichlorozirconium (5) have been prepared from the corresponding lithium cyclopentadienide (l). The crystal structure of cyclopentadienyl complex2 has been established by X-ray analysis. The coordination O→Zr bond in compound2 exists both in the crystalline state and in solutions. No coordination of this type was observed in complexes3–5. Synthesized complexes2–5 are discussed in comparison with their sulfur-containing analogs.
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  • 38
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    Pharmaceutical research 13 (1996), S. 1003-1007 
    ISSN: 1573-904X
    Keywords: molecular simulation ; interfacial energy ; wettability ; crystal structure ; Monte Carlo method ; potential energy calculations ; contact angle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. This study describes the development and application of a molecular simulation technique for investigating the solid-liquid interface. It attempts to relate the molecular and crystal structure to the observed wettability of solids. Methods. Molecular simulations have been carried out for the crystal-water interface of a series of N-n-alkyl-D-gluconamide crystals using the Monte Carlo technique. The molecular system simulated consisted of a layer of water bounded by two crystal slabs. The interfacial potential energies were calculated for the crystal-water interactions and compared with experimental enthalpy values obtained from contact angle measurements. Results. The simulations clearly reveal the distinct hydrophilic and hydrophobic nature of the respective (010) and (010) faces of these compounds. The distribution of water at the interface observed in the simulations is in accord with the nature of the crystal faces. The calculated interfacial potential energies are in the right ball park, but consistently higher than the experimental values. The disparity, however, is justifiable, resulting from the highly simplified model simulated. Conclusions. Using the developed molecular simulation technique one can calculate the wettability of a solid given the crystal structure. This approach represents an important step towards the goal of engineering crystals with desired wettability characteristics.
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  • 39
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    Colloid & polymer science 274 (1996), S. 1006-1011 
    ISSN: 1435-1536
    Keywords: Syndiotactic polypropylene ; cold stretching ; chain conformation ; crystal structure ; crystallization behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of the chain conformation on the crystallization behavior of cold-drawn syndiotactic polypropylene (sPP) has been investigated. The conformational and structural changes depending on drawing conditions and thermal treatments has been observed by x-ray diffraction, infra-red spectroscopy and modulated differential scanning calorimetry. A nucleation and crystal growth model is introduced, which explains the low crystallinity of cold-drawn sPP.
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  • 40
    ISSN: 1572-9605
    Keywords: Y0.4Pr0.6Ba2−xCaxCu3O7−δ ; superconductivity ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Y0.4Pr0.6Ba2−xCaxCu3O7−δ polycrystalline samples were prepared and investigated. The Ca substitution led to a structural variation toward tetragonal symmetry, possibly due to the structural modification within the Cu(1)O layer. Superconductivity and metallic conduction were recovered whenx≥0.2, giving one more evidence for the existence of the ion-size effect at the Ba site.
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  • 41
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1087-1093 
    ISSN: 0887-624X
    Keywords: topotactic polymerization ; 3-aminocrotonamide ; radiation polymerization ; crystal structure ; condensation polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radiation-induced solid-state polymerization of 3-aminocrotonamide (3-amino-2-butenamide) was carried out at room temperature, in open air atmosphere and under vacuum condition. The polymer obtained was white powder, soluble in methanol, but insoluble in water. The nature of polymers were investigated by IR, UV, x-ray, DP-MS, and elemental analysis to elucidate the mechanism of the polymerization. The polymer was crystalline with melting point in the range of 245-255°C. The cell parameters and space group of monomer and polymers were determined from powder x-ray diffraction patterns. The similarity of crystal structures of monomer and polymer indicated a topotactic polymerization. It was shown by spectroscopic investigations and elemental analyses that the polymerization proceeds by condensation reaction with evolution of one mole ammonia per two combined moles of monomer through a free radical mechanism. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 42
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    Journal of inclusion phenomena and macrocyclic chemistry 26 (1996), S. 153-159 
    ISSN: 1573-1111
    Keywords: Cadmium cyanide ; crystal structure ; clathrate ; mineralomimetic chemistry ; dimethyl carbonate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Cd(CN)2·(CH3O)2CO (1) contains a mineralomimetic framework of Cd(CN)2 analogous to the low temperature form of cristobalite. The host framework is isostructural to those of previously reported Cd(CN)2·G compounds (G = CHCl2CH2Cl2, (CH3)2CHBr3). The dimethyl carbonate molecules in the adamantane-like cage display orientation disorder associated with the location of the carbonyl oxygen atom.
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  • 43
    ISSN: 1573-1111
    Keywords: Cyanocuprate(I) complex ; crystal structure ; three-dimensional framework ; bifurcated cyano group ; N-(2-aminoethyl)piperazine ; hydrogen-bond ; dimeric onium guest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The title inclusion compound [{NH2(CH2CH2)2NCH2CH2NH2}2H][Cu4(CN)7] was obtained as single crystals from an aqueous solution containing CuCN, KCN, andN-(2-aminoethyl)piperazine. It crystallizes in the monoclinic space groupP2/n,a = 12.3829(9),b = 8.5970(9),c = 12.6633(7) Å, β = 109.984(5)°,z = 2,R = 0.035 for 2921 independent reflections. The inclusion structure is composed of the hydrogen-bonded dimeric onium guest [{NH2(CH2CH2)2NCH2CH2NH2}2H]3+ and the negatively-charged three-dimensional host [CU4(CN)7]3− in which the CN-bridged framework Cu(I) atoms are all tetrahedral. A polyacene-like one-dimensional array of hexagons cornered by Cu(I) atoms and edged by -CN- linkages is arrayed in parallel to theb axis and stacked approximately along the c axis. The Cu(I) corner shared in the one-dimensional array extends an N-coordinate CN group along the c axis to a pair of unshared Cu(I) corners for which the C end behaves as a bifurcated ligand to build up the three-dimensional host structure. The cavity is composed of two networks of the hexagons at the top and bottom and pillared by six 〉CN- groups and accommodates a dimeric guest ofN-(2-aminoethyl)piperazinium cations protonated at each 4-N with the cations being hydrogen-bonded to each other through the 2-NH2 groups sharing another H+.
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  • 44
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    Journal of inclusion phenomena and macrocyclic chemistry 26 (1996), S. 197-207 
    ISSN: 1573-1111
    Keywords: Crown ether ; nitromethane complex ; coordination isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Single crystal X-ray diffraction analyses of two nitromethane complexes of furanotribenzo-21-crown-7 (1 and2) and the nitromethane complex of dibenzo-2l-crown-7 (3) are reported. The two nitromethane complexes1 and2 are polymorphic in that the macrocyclic ring adopts the ‘dentist's chair’ conformation in both structures, with a single nitromethane molecule coordinating to either the lower, concave (1) or upper, convex (2) face of the crown ether. Complex3 adopts an entirely different conformation with a coplanar arrangement of the crown ether oxygen atoms binding a single nitromethane molecule.
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  • 45
    ISSN: 0947-6539
    Keywords: azadienes ; azepines ; cycloadditions ; Fischer carbenes complexes ; reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Amino-1-azadienes 1 react with α,β-unsaturated Fischer carbene complexes at -40°C to give stereoselectively a variety of substituted 3H-4,5-dihydroazepines 3; similarly, 1-hydroxy-1-azadienes (α,β-unsaturated oximes) 6 afforded the corresponding azepine derivatives 7. Chiral, nonracemic carbene complexes 11 gave azepines 12-13 (d.e. = 40-44%) upon reaction with oxime 6a; the major isomers were obtained in a diastereomerically and enantiomerically pure form (45-50% overall yield) after crystallization. An X-ray structure of 12a allowed assignment of the absolute stereochemistry. The acid hydrolysis of azepines synthesized provided racemic and enantiomerically pure 1,6-dicarbonyl compounds (±)-5, (±)-9, and (-)-14, as well as diol (-)-15. The mechanism of the reaction of 1 and 2 was investigated by multinuclear (1H, 13C, 15N, and 183W) NMR characterization of four intermediates (A, B, C, and D) at low temperature. The experimental sequence of events involves: i) 1,2-nucleophilic addition of the unsubstituted imine nitrogen of 1 to the metal carbene function (zwitterion A, -60°C), ii) cyclization to the seven-membered ring with 1,2-migration of the pentacarbonyl metal (zwitterion B, -40°C), iii) reductive elimination and coordination of the metal to the amine nitrogen (intermediate C, -40°C), and iv) thermal decomplexation and tautomerization (intermediate D and compound 3, above -20°C).
    Additional Material: 6 Ill.
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  • 46
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 47
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 48
    ISSN: 0947-6539
    Keywords: homolytic cleavage ; organometallic compounds ; photochemistry ; rhenium complexes ; time-resolved spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MLCT excitation of the complexes [Re(R)(CO)3(α-diimine)] (R = Me, Et, benzyl (Bz); α-diimine = iPr-PyCa, R′-DAB) results in the homolysis of the Re-R bond leading to the formation of radicals R. and [Re(CO)3(α-diimine)]. as primary photoproducts. The quantum yield of this photoprocess is dependent on the alkyl group used. For R = Me, the quantum yield is low (10-2) and depends on the temperature and excitation wave-length, whereas for R = Et and Bz the quantum yield is near unity and independent of T and λexc. The reaction is shown to proceed via a σ(Re-R)π* excited state that is rapidly (〈 20 ps) populated by a nonradiative transition from the optically excited MLCT state. Time-resolved IR and UV/Vis absorption spectra studied in the ns-μs and ps-μs time domains, respectively, show that the σπ* excited state is rather long-lived (τ ≈ 250 ns) in noncoordinating solvents; the dissociation of the Re-R bond from this state is strongly accelerated by polar or coordinating solvents (τσπ*〈 20 ps). The σπ* excited state is spectroscopically characterized by a (presumably σπ* → MLCT) transition at approximately 500 nm and by CO stretching frequencies closely resembling their ground-state values. The relative energies of the MLCT and reactive σπ* states, controlled by the nature of the alkyl lig-and, determine the photoreactivity of the complexes.
    Additional Material: 8 Ill.
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  • 49
    ISSN: 0947-6539
    Keywords: dendrimers ; high-spin molecules ; photochemistry ; polycarbenes ; solid solutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A “starburst”-type nonadiazo compound was designed and synthesized by using the cyclotrimerization of 3,5-dibenzylphenyl ethynyl ketone as a key step. The diazo compound was photolyzed in methyltetrahydrofuran solid solution at cryogenic temperatures and analyzed by means of Faraday magnetometry and EPR spectroscopy. While the m-phenylene-connected nonacarbene was predicted to have a nonadecet (S = 9) ground state, the magnetic data of the photoproduct was more consistent with a pentadecet (S = 7) species. The result was interpreted in terms of the intramolecular cross-linking between the carbene centers by the determination of both the amount and the multiplicity of the spin. In the “starburst”-type polycarbenes with extended branching, the reactive carbene centers are able to approach one another and thus appear to readily recombine. This study highlights one of the limitations of the extension of the carbene network by way of flexible “starburst”-type structures.
    Additional Material: 8 Ill.
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  • 50
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 382-384 
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; chirality ; enolates ; hydrogen bonds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of acetophenone with tetrabutylammonium hydroxide affords the tetrabutylammonium enolate of phenyl (2-hydroxy-2-phenyl)propyl ketone. The crystal structure of this chiral enolate shows intramolecular hydrogen bonding between the hydroxyl group and the enolate oxygen atom. Furthermore, the α-methylene units of the ammonium counterion form hydrogen bonds to the basic enolate C and O atoms and to the O atom of the hydroxy group. This three-point bonding occurs selectively on the Re,Re side, a phenomenon which may be responsible for the direction of diastereo-selectivity in the epoxide-forming reaction of the enolate with N-bromosuccinimide.
    Additional Material: 1 Ill.
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  • 51
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    Chemistry - A European Journal 2 (1996), S. 390-397 
    ISSN: 0947-6539
    Keywords: band structures ; hypervalent bonding ; semiempirical calculations ; tellurium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bonding in the recently reported Cs3 Te22 phase, which contains both Te8 rings and remarkable Te6 sheets, is studied by approximate molecular orbital theory. Our focus is on the geometric and electronic features of the unique 2,3-connected Te net found as a substructure in this phase. The calculations show that both the linear and T-shaped Te geometries in the 2,3-connected Te net of Cs3 Te22 are determined by their particular electron count. Both types of tellurium atoms are hypervalent; we make connections to other well known hypervalent molecules, such as XeF2, I3-, and BrF3. Several possible variations and distortions of this net are discussed, all of which are found to be less stable. The discrete crown-shaped Te8 units that appear in the phase show normal covalent bonding and should occur in smaller molecular entities, too. According to our computations, Cs3 Te22 should be metallic. Two structurally related phases, CsTe7 and Cs2 Te15, are suggested.
    Additional Material: 10 Ill.
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  • 52
    ISSN: 0947-6539
    Keywords: carbon-carbon coupling ; carbonyl complexes ; hafnium complexes ; ketenylidene complexes ; zirconium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biscyclopentadienyldicarbonyl derivatives of zirconium(II) and hafnium(II) ([MCp2(CO)2]; M=Zr, Hf) promote the reductive coupling of coordinated carbon monoxide to give, in the presence of N,N-dialkylcarbamtes of the tetravalent metals [M(O2CNR2)4], the ketenylidene complexes [M3Cp2(μ2-CCO)-(μ3-O)(O2CNR2)6] (1 a: M=Zr, R=Et; 1 b: M=Zr, R=iPr; 2: M=Hf, R=iPr). The yields of the isolated zirconium complexes are as high as 60%, while that of the hafnium derivative is 40%. The X-ray crystal structure analysis of 1 b shows that it consists of trinuclear molecules, with the three zirconium atoms held together by the bidentate C2O ligand, by the tridentate bridging oxide and by the bidentate carbamato groups. Labelling experiments with [ZrCp2(13CO)2] show that the ketenylidene ligand originates from the coordinated CO groups. These ketenylidene complexes, which are rare examples of compounds containing a CCO but no CO ligand, are characterized by an intense IR band at about 2015 cm-1, associated with the bridging C2O ligand. The ketenylidene group of 1 b was readily removed and replaced by a bidentate μ-oxo ligand of the same hapticity by reaction with carbon dioxide or acetone or by thermal decomposition. The resulting product [Zr3Cp2(μ-O)(μ3-O)-(O2CNiPr2)6] (3) crystallizes in the same space group as 1 b and with similar cell constants and bond parameters.
    Additional Material: 4 Ill.
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  • 53
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 458-461 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; barbaralanes ; borabarbaralanes ; Cope rearrangement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of MgCOT(thf)x with tBuBF2 or PhBCl2 affords the first 9-borabarbaralanes 2 (C8H8BR, a: R = tBu; b: R=Ph). With the aminoboron dihalides BCl2NiPr2 and BCl2N(SiMe3)tBu 9-borabicyclo[4.2.1]-nona-2,4,7-trienes 3 (a: R=NiPr2, b: R=N(SiMe3)tBu) and the trans-9-borabicyclo[4.3.0]nona-2,4,7-triene 4 are obtained. The bicyclic compounds 3a and 3 b are converted into 9-borabarbaralanes 2c and 2 d, respectively, by irradiation in solution as well as by heating. All 9-borabarbaralanes 2 are fluxional in solution. In the crystalline state, the B-phenyl derivative 2b displays a well-ordered van der Waals crystal structure. The theoretical prediction that the degenerate Cope rearrangement in barbaralanes will be retarded by π-acceptor groups in the 9 position has been verified. Quantum chemical calculations employing density functional theory support and help interpret the experimental findings. The isoelectronic 9-barbaralyl cations, in contrast, have such high Cope barriers that other rearrangement pathways are followed instead.
    Additional Material: 1 Ill.
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  • 54
    ISSN: 0947-6539
    Keywords: density-functional theory ; liquid water ; molecular dynamics simulations ; NMR chemical shifts ; solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solvent effect on the NMR chemical shielding in liquid water is calculated from a combination of molecular dynamics simulations and quantum chemical calculations for protons and 17O. The simulations are performed with three different potentials, ab initio as well as empirical ones, to study the influence of the force field. From the liquid configurations obtained in these simulations, molecules are randomly chosen together with neighbouring molecules to give clusters of water typical for the liquid at the selected temperature and density. Different cluster sizes are studied. The clusters are treated as supermolecules in quantum chemical calculations of chemical shifts by sum-over-states density functional perturbation theory with individual gauge for localised orbitals. The influence of the quantum chemical method is studied with an ab initio coupled Hartree-Fock gauge including atomic orbitals calculations with different basis sets for a selected cluster. An average over clusters yields the chemical shielding in the liquid at the selected temperature and density. The calculated values for the gas-liquid shift, which are in best agreement with experiment, are -3.2 ppm (exp. -4.26 ppm) for the proton and -37.6 ppm (exp. -36.1 ppm) for 17O, but the results depend strongly on the chosen interatomic potential.
    Additional Material: 1 Ill.
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  • 55
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    Chemistry - A European Journal 2 (1996), S. 1053-1059 
    ISSN: 0947-6539
    Keywords: chalcogenides ; periodic trends ; redox reactions ; soft chemistry ; transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The increase in energy of the sp anionic band on going from oxides to the less electronegative sulfides, selenides, or tellurides (with a similar trend in neighboring columns) facilitates anion-cation redox interactions involving the d levels of transition metal cations and the sp levels of anionic species. The interactions can induce phase transitions or gradual change within a given structural model. When a cation is reduced by electron transfer to its d levels from the sp band, holes appear at the top of the latter. Interesting soft chemistry can be carried out based on redox processes that neutralize the holes with electrons. This approach also allows particular structural types to be stabilized. Three structural domains can be recognized amongst the transition elements: 1) on the left-hand side of the periodic table layered structures are observed involving M4+ and (chalcogen)2- ions; 2) formation of sets of metal-metal bonds is then observed, the geometry of which depends on both the initial electron population and the electron transfer to the metal; 3) on the right-hand side the metals in their highest oxidation state are no longer active, and the holes at the top of the sp band are taken up by a catenation of the anions, which can lead to full polymerization of the anionic sublattice.
    Additional Material: 8 Ill.
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  • 56
    ISSN: 0947-6539
    Keywords: cyclic voltammetry ; dendrimers ; metallodendrimers ; terpyridine ; X-ray photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of iron-containing metallodendrimers from the zeroth to the third generation was synthesized and characterized. The iron(II) ion of these metal complexes is encapsulated within a hydrophobic polyether dendritic envelope. X-ray photoelectron spectroscopy analysis revealed that the bonding environment of the iron atom was essentially ronment of the iron atom was essentially the same in dendrimers of different generations. However, cyclic voltammetry studies indicated that the reversibility of the metal redox process decreased in the higher-generation dendrimers. These observations were similar to those of a related electrochemical study conducted on the redox protein cytochrome C, in which the decrease in electron transfer reversibility was explained as a result of the increasing remoteness of the metal ion of the higher-generation dendrimers from the electrode surface.
    Additional Material: 6 Ill.
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  • 57
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    Chemistry - A European Journal 2 (1996), S. 1112-1114 
    ISSN: 0947-6539
    Keywords: coordination ; crystal structure ; halogen compounds ; magnesium compounds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MgBr2·OEt2 (1), which is commercially available and has been examined by different methods in the past, was obtained in crystalline form as a by-product of the reaction of amine-stabilised A1C1 solution with mesitylene magnesium bromide. The following unexpected structure was obtained by X-ray techniques: five-coordinate magnesium centres form trigonal bipyramids, which are connected by two common bromine atoms into chains. Structural details and especially the relationship with solid MgBr2, MgBr2·(OEt2)2 and MgI2·(OEt2)2 (2) are discussed in order to illuminate the unusual bonding in 1.
    Additional Material: 2 Ill.
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  • 58
    ISSN: 0947-6539
    Keywords: iron complexes ; magnetic susceptibility ; Mössbauer spectroscopy ; phasetransitions ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≍285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin-state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin-state trapping is triggered by an additional structural phase transition of the system.
    Additional Material: 8 Ill.
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  • 59
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    Chemistry - A European Journal 2 (1996), S. 1164-1172 
    ISSN: 0947-6539
    Keywords: allylations ; allylsilanes ; double stereodifferentiation ; ephedrine ; homoallylic alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure homoallylic alcohols 5, which are important building blocks in organic synthesis, are obtained with an ee of greater than 99% and a yield of 75-95% by cleavage of the secondary homoallylic ethers 4 using sodium in liquid ammonia. The ethers 4 are formed with excellent diastereoselectivity and in 52-89% yield by treatment of the aldehydes 1 with the trimethylsilyl ether of N-trifluoroacetylnorpseudoephedrine (2) in the presence of a catalytic amount of TMS triflate or TMS borontriflate, followed by addition of allylsilane 3. Nearly all achiral aliphatic aldehydes employed gave a diastereoselectivity of over 99:1. With the chiral aldehydes 24, the difference between matched and mismatched pairs was low; this reveals that there is strong reagent control.
    Additional Material: 2 Tab.
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  • 60
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 61
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    Chemistry - A European Journal 2 (1996), S. 1201-1203 
    ISSN: 0947-6539
    Keywords: alkali metals ; hydrogen ; metallic hydrogen ; metallization densities ; periodicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the density-dependent metal-nonmetal transition (MNMT) for the Group 1 elements hydrogen, rubidium and caesium. Remarkably, the experimentally observed metallization densities agree closely with those predicted from the 1927 classical theory of K. F. Herzfeld, which outlines the critical conditions necessary for the metallization of any element of the periodic system. The metallization densities of the alkali metal elements are also consistent with the quantum mechanical theory of the MNMT, as first set out by Sir Nevill Mott.
    Additional Material: 3 Ill.
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  • 62
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    Chemistry - A European Journal 2 (1996) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 63
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    Chemistry - A European Journal 2 (1996), S. 1514-1517 
    ISSN: 0947-6539
    Keywords: calcium compounds ; calorimetry ; nitrides ; ternary metal nitrides ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The energetics of ternary oxide formation is reasonably well understood, but little is known of the energetics of ternary nitride formation. We have developed new procedures for high-temperature oxide melt solution calorimetry on metal nitrides and employed them to study compounds in the Ca/Zn/N system. The calorimetry utilized the easy reduction of MoO3 in the solvent to supply a pathway for rapid oxidation of “N3-” to N2 gas. These experiments represent the first high-temperature solution calorimetry of ternary metal nitrides. The results indicate that Ca3N2 acts as a basic nitride analogous to CaO in oxide systems, while Zn3N2 acts as an acidic nitride (“N3-” acceptor) in this ternary nitride system.
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  • 64
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    Chemistry - A European Journal 2 (1996), S. 1509-1513 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; binding studies ; crystal packing ; drug design ; hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the design of novel protein ligands one of the major challenges is the replacement of functional groups to modify and improve the binding characteristics. Often nitrogen- and oxygen-containing groups are exchanged, or both atoms occur in a competitive situation. We have investigated the hydrogen-bonding abilities of oxygen atoms covalently bound to two non-hydrogen atoms of which at least one is formally assigned to an sp2-type hybridization. In particular, examples in which such oxygen atoms compete with nitrogen atoms in the same molecular segment have been studied. Based on interaction energies obtained from ab initio calculations for complexes of these molecules with water, the oxygen atoms can be classified as rather weak hydrogen-bond acceptors; nitrogen atoms present in the same fragment exhibit much stronger interaction energies. The ab initio results are confirmed by the relative frequencies with which oxygen and nitrogen atoms are found to be involved in hydrogen bonding in the crystal structures of organic molecules containing the fragments of interest.
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  • 65
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    Chemistry - A European Journal 2 (1996), S. 1533-1536 
    ISSN: 0947-6539
    Keywords: catalysis ; dehydrogenations ; oxidations ; ruthenium complexes ; secondary alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly efficient ruthenium-catalyzed Oppenauer-type oxidations of secondary alcohols to ketones have been developed. The catalytic system consists of [(PPh3)3RuCl2] (1) and K2CO3 or [(C4Ph4COHOCC4Ph4)(μ-H)(CO)4Ru2] (2) in refluxing acetone. The catalytic reaction is of high efficiency and permits a catalyst: substrate ratio of 1:1000 at 56 °C. In some cases the initial turnover rate exceeds 1500 h-1. The reaction was found to be general and compatible with double bonds and oxidation-sensitive aromatics. With some allylic alcohols, isomerization to saturated ketones took place. The reaction proceeds by ruthenium-catalyzed dehydrogenation of the alcohol and subsequent hydrogen transfer to acetone. No primary kinetic isotope effect was observed for the catalytic reaction when α-deuterated 1-phenylethanol was employed as substrate (kH/kD=1.1); this shows that β-hydride elimination from a ruthenium alkoxide intermediate is not the rate-limiting step.
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  • 66
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    Chemistry - A European Journal 2 (1996), S. 4-6 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 67
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    Chemistry - A European Journal 2 (1996), S. 7-8 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 68
    ISSN: 0947-6539
    Keywords: carbon ligands ; diynes ; iridium compounds ; metallacumulenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [IrH2Cl(PiPr3)2] (2) with the pentadiyne derivative HC≡C—C≡C—CPh2OH (1) yields the five-coordinate compound [IrH(C≡C—C≡CPh2OH)Cl(PiPr3)2] (3), which photochemically rearranges to give the vinylidene-substituted isomer trans-[IrCl(=C=CH-C≡CPh2OH)(PiPr3)2] (4). On treatment of 3 with pyridine, the octahedral complex [IrH (C≡C—C≡CPh2OH)Cl(py)(PiPr3)2] (5) is formed. While attempts to eliminate water from 4 (or 5) failed, the reaction of 3 with one equivalent of trifluorosulfonic acid anhydride and two equivalents of triethylamine led to the formation of trans-[IrCl(=C=C=C=C=CPh2)(PiPr3)2] (6), which is the first neutral transition-metal complex containing a C5R2 ligand. The X-ray structural analysis of 6 reveals a perfect square-planar coordination geometry around the metal centre and an almost linear IrC5 chain with Ir-C—C and C—C—C bond angles of 174-179°.
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  • 69
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    Chemistry - A European Journal 2 (1996), S. 45-49 
    ISSN: 0947-6539
    Keywords: exchange processes ; kinetics ; NMR spectroscopy ; zirconium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have shown that it is possible to inhibit the transfer of magnetization in a system with several exchanging sites in dynamic equilibrium, as in a mixture of cis- and trans-ZrCl4L2 with excess free ligand L (L = (CH3O)3PO). The forward and backward reaction rates involving two selected sites can be studied while the effect of competing exchange processes is “quenched”. This can be achieved either by selective inversion of the magnetization of the two chosen sites in the course of the reaction interval, or alternatively by inversion of the magnetization of all other sites in the exchange network. The rate of exchange from the free to the cis site was determined to be kcis←free = 0.018 s-1. In the usual methods, this process would tend to be overshadowed by the almost two hundred times faster competing exchange process from the cis to the trans site (Ktrans←cis = 3.32 s-1).
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  • 70
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    Chemistry - A European Journal 2 (1996), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 71
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    Chemistry - A European Journal 2 (1996), S. 9-18 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; azaenolates ; NMR chemical shifts ; peptides ; Ramachandran maps ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structures and conformations of the azaenolate lithium salts of amides (formamide, acetamide, and N-methylacetamide) and of the dipeptide model N-formylalaninamide were investigated by means of ab initio MO theory. Four possible structures of the lithiated C-enolates of acetamide were also included in the study. All structures were calculated at the HF/6-31+G(d) and MP2(fc)/6-31 + G(d)/HF/6-31 + G(d) levels; the lithiated azaenolates of formamide were also investigated at higher theoretical levels (up to MP4(fc)/6-311 + G(d,p)/MP2(fc)/6-311 + G(d,p)). For the lithiated azaenolates of all amides investigated, the most stable structure contains a four-membered ring in which the lithium ion is complexed by the oxygen and nitrogen atoms; the substituents attached to the carbon and nitrogen atoms of the azaenolate are in a cis arrangement. The lithiated azaenolates of acetamide are predicted to be more stable than the corresponding C-enolates. To simulate solvation, calculations on complexes of the lithiated azaenolates of formamide with up to three molecules dimethyl ether were also performed, and all azaenolates of amides were also reoptimized by ab initio reaction-field calculations. Both solvation models reduce the preference for lithium-chelated cis structures. The Ramachandran maps of the dilithiated bis(azaenolate) of N-formylalaninamide (having cis or trans arrangements of the azaenolate substituents) were scanned by MNDO calculations for conformational accessible regions. Thirteen stable structures were subsequently optimized at the HF/6-31 + G(d) ab initio level. The global minimum resembles a peptide in C7 conformation, but other conformations, not known for peptides, are close in energy. The structures of dimers of the lithiated azaenolates of N-methylacetamide and of glycinaldehyde were also calculated. The NMR chemical shielding of carbon, nitrogen, and oxygen atoms in all structures were predicted ab initio by using the gauge-including atomic orbital (GIAO) method.
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  • 72
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    Chemistry - A European Journal 2 (1996), S. 50-57 
    ISSN: 0947-6539
    Keywords: alkenes ; catalysis ; dihydroxylations ; electrophilicity ; ruthenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative ruthenium catalysis (0.07 molequiv RuCl3·(H2o)3, 1.5 molequiv NaIO4, EtOAc/CH3CH3CN/H2O 3:3:1), beyond the usual C—C bond cleavage to give dicarbonyls, has been shown to syn-dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently. The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols. Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage. Reactions with substrates containing one or more electron-with-drawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields. The diastereoselectivity of the present “flash” dihydroxylation, anti to the existing α-stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor. Sodium metaperiodate is still the best co-oxidant for the catalytic reaction. Aqueous acetonitrile (approximately 86%) as an alternative solvent system was found to give better yields of 1,2-diols than the original solvent system in some cases.
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  • 73
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    Chemistry - A European Journal 2 (1996), S. 475-475 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 74
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    Chemistry - A European Journal 2 (1996), S. 502-510 
    ISSN: 0947-6539
    Keywords: alkynes ; C-glycosides ; cobalt complexes ; cyclizations ; enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of gluconolactone 2 with allylmagnesium bromide at low temperatures afforded ketopyranose 3, which could easily be converted into open-chain ketoses (R)-6 and (S)-6. Their reaction with lithioacetylide 9 afforded propargylic alcohol derivatives (R)-10 and (S)-10, which could not be cyclized directly to the desired C-ketosides. They were converted by standard procedures into (R)-14 and (S)-14 and then into dicobalthexacarbonyl complexes (R)-16 and (S)-16. A facile acid-catalyzed ring closure gave the desired C-ketosides (R)-18 α/β and (S)-18α/β, respectively, in different ratios. In order to demonstrate that removal of the protective groups and hydrogenation of the CC triple bond proceed smoothly, (R)-18 α was transformed into the deprotected target molecule (R)-1 α. For the assignment of the new chiral centers at C-2/2′ and at C-8, (S)-18α was transformed into azido derivative (S)-22α, which underwent intramolecular cycloaddition to afford the spiro derivative (S)-25α. Because of the conformational constraints in this molecule, unequivocal configurational assignment was possible with the help of NMR data.
    Additional Material: 1 Ill.
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  • 75
    ISSN: 0947-6539
    Keywords: carbonyl complexes ; chiral ligands ; iron complexes ; phosphorus ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Secondary phosphines such as HPPh2 and to the cationic iron dienyl complex [η5-(1R)-ethylnopadienyl)Fe-(CO)3]+ (1) by nucleophilic addition. The phosphonium salt initially formed is readily deprotonated to yield an optically active tertiary phosphine [(n4-(1 R)-ethylnopadienePPh2)Fe(CO)3] (2b). A similar reaction also occurs with [C6H7Fe-(CO)3]+ (3) and [C7H9Fe(CO)3]+ (4) to give [(C6H7PPh2)Fe(CO)3] (5) and [(C7H9PPh2)Fe(CO)3] (6) in good yields. The mechanism of formation of these novel phosphines is discussed. Complex 2 b crystallizes in the space group P212121 (no. 19); 5 crystallizes in the space group P21/c (no. 14). Like other monodentate optically active phosphines, 2 b is capable of coordinating to transition metal complexes. It forms palladium complexes on reaction with [{μ-chloro(allyl)palladium}2] as well as with [{μ-chloro[(N,N-dimethylamino-kN-2-methyl)phenyl-kC]palladium}2] (11). The latter reaction product crystallizes in the space group P31 (no. 144).
    Additional Material: 3 Ill.
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  • 76
    ISSN: 0947-6539
    Keywords: carbohydrates ; cyclodextrin analogues ; cyclooligomerizations ; glycosylations ; nanotubes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient polycondensation-cyclization approach to the synthesis of cyclodextrin analogues is demonstrated by the preparation of cyclohexaoside 1 and cyclooctaoside 2. The key intermediate, disaccharide 3, bearing the cyanoethylidene group as a glycosyl donor function and the trityloxy group as a glycosyl acceptor function was prepared in 15 steps starting from L-rhamnose and D-mannose. The crucial cyclooligomerization of the disaccharide monomer 3 was carried out in the presence of TrClO4 as a promoter with the use of ultra-dry conditions at normal concentrations. This reaction led to formation of the cyclic oligosaccharides 28 and 29 (in 34 and 31% yield, respectively), which were deprotected to afford 1 and 2, respectively. The X-ray crystal structural analysis of the cyclooctaoside 2 reveals a cylindrical shape for the cyclic oligosaccharide with C4 symmetry. Individual molecules of 2 are arranged perfectly in stacks that form nanotubes in the solid state.
    Additional Material: 14 Ill.
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  • 77
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    Chemistry - A European Journal 2 (1996) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 78
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    Chemistry - A European Journal 2 (1996), S. 624-633 
    ISSN: 0947-6539
    Keywords: catenanes ; macrocycles ; rotaxanes ; self-assembly ; tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general stepwise approach is described for the preparation of tetrathiafulvalene (TTF)-based linear and monoand dimacrocyclic compounds incorporating one or two 1,4-dioxyphenylene, 9,10-dioxyanthrylene, or 1,5- or 2,6-dioxynaphthylene units from readily available starting materials. By utilizing the π-π stacking interactions of the TTF unit with the dipyridinium dication of 1,1′-[1,4-phenylenebis (methylene)] bis-4,4′-bipyridinium bis(hexafluorophosphate), a rotaxane and two [2]catenanes were synthesized starting from the linear and monomacrocyclic compounds, respectively. From the dioxyphenylene-based dimacrocycle, three [3]pseudocatenanes (trans, cis, and a mixture of cis/trans isomers) were obtained with the trans compound as the major product. From the dioxyanthrylene dimacrocycle, only the trans-[3]pseudocatenane was obtained. Catenane products were formed quantitatively from the 1,5-dioxynaphthylene dimacrocycle in a template-directed reaction, affording a trans-[3]pseudo-catenane together with a [4]pseudocatenane (mixture of cis/trans isomers). From the 2,6-dioxynaphthylene dimacrocycle, a cis-[3]pseudocatenane was obtained as the major product and a trans-[3]pseudocatenane as the minor one. For the [3]pseudocatenanes (i.e., both the cis and trans catenanes), in which the TTF units were clamped by the tetracationic macrocycle, isomerizations were completely prevented even in the presence of trifluoroacetic acid. All new rotaxanes and catenanes were characterized by electrospray mass spectrometry, and the cis- and trans- [3]pseudocatenanes were additionally investigated by 1H NMR spectroscopy. The electrochemical and spectral properties of the rotaxane and the catenanes are reported. Catenane formation increases the redox potentials of the TTF unit. The results demonstrate the versatility of TTF as a building block in the construction of supramolecular structures.
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  • 79
    ISSN: 0947-6539
    Keywords: chemoselectivity ; cinchona alkaloids ; clathrates ; osmium tetroxide ; spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrobromination of quinidine (1) with fuming HBr furnished diastereomeric secondary bromides 2a and 2b in 82% yield. After acetylation the resulting bromides 2a-Ac and 2b-Ac could be separated na dconverted stereospecifically into ethylidene rubanes Z)-4 and (E)-4, respectively. cis-Dihydroxylation of (Z)-olefin 4 with OsO4 was shown to be feasible by two catalytic variants, giving the two diastereomeric diols 5a and 5b, separable by chromatography. A simple onepot procedure was developed for converting the sterically hindered 1,2-secondary, tertiary diols stereospecifically into spiroepoxides (5a 6a-Ac; 5b 6b-Ac). Our procedure involves overall inversion of configuration. The procedure complements the Kolb-Sharpless route to epoxides from 1,2-disecondary diols with overall retention of configuration. The other two diastereomeric spiroepoxides 6c and 6d were prepared in one pot under different conditions (chloramine T, then alkali). Two unprecedented tricyclic allylic N,O-acetals (Z)-7 and (E)-7 were also obtained. The structure of spiroepoxide 6c (as a CH2Cl2 monosolvate) and of tricyclic olefinic N,O-acetal (E)-7 was corroborated by X-ray crystallography.
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  • 80
    ISSN: 0947-6539
    Keywords: asymmetric alkylations ; chiral auxiliaries ; kinetics ; organolithium compounds ; stereoselective syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of the configurationally labile α-phenylselenoalkyllithium compound 8 with 1,2-bisdimethylaminocyclohexane 15 led to two diastereomeric complexes 13 and 14 in a 7:3 ratio. Owing to ligand acceleration the complexes 13 and 14 added more rapidly to benzaldehyde than the uncomplexed organolithium compound 8. Trapping of complexes 13 and 14 by benzaldehyde was shown to occur more rapidly than their equilibration. This corresponds to non-Curtin-Hammett kinetics, in which enantiomeric enrichment in the products reflects the equilibrium ratio of the complexes 13 and 14.
    Additional Material: 1 Ill.
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  • 81
    ISSN: 0947-6539
    Keywords: amphiphiles ; cytomimetic chemistry ; phosphitylation ; polyprenols ; vesicles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Identical- and mixed-chain di(polyprenyl) phosphates, derived from 3-methyl-2-buten-1-ol, (E)-geraniol, (E,E)-farnesol, (E,E,E)-geranylgeraniol, (R)-citronellol, or (R)-tetrahydrogeraniol have been synthesized by phosphitylation and oxidation with iodine/water. These phosphates gave organized systems in water, in particular vesicles, the physical properties of which were studied by photon correlation spectroscopy, electron microscopy, entrapment of a fluorescent dye (calcein), 31P NMR, stopped-flow/light-scattering studies, and fluorescence polarization with lipophilic probes. Interdigitation of mixed-length phosphates was not found to have any favorable effect on the stability of the vesicles. The C〉15 vesicles were formed despite the fact that they are composed of only one molecular species and are devoid of any reinforcer, but those with two geranyl chains appeared to be rather fragile. Phosphates containing C5 chains are soluble in water. The results obtained lend weight to the hypothesis that polyprenyl phosphates might have been primitive membrane constituents, and stimulate the search for appropriate reinforcers.
    Additional Material: 9 Ill.
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  • 82
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    Chemistry - A European Journal 2 (1996), S. 812-814 
    ISSN: 0947-6539
    Keywords: alkanes ; cracking ; isomerizations ; sulfur compounds ; superacids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel family of inorganic aprotic superacids has been found. Oxochlorides and chloride of sulfur combined with aluminium halides (SOCl2·n AlX3, SO2Cl2·n AlX3, MeSO2Cl·n AlX3, CF3SO2Cl·n AlX3, S2Cl2·n AlX3; n = 2 or 3, X = Br or Cl) are found to be effective promoters for the cracking and isomerization of alkanes at room temperature.
    Additional Material: 2 Tab.
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  • 83
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    Chemistry - A European Journal 2 (1996), S. 832-837 
    ISSN: 0947-6539
    Keywords: cyclophanes ; macrocyclisations ; molecular ribbons ; nanostructures ; repetitive syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The longest molecular ribbons known to date (3-10), composed of a series of [3.3]metacyclophane units, have been synthesised by means of a repetitive synthetic strategy. These multiple ring systems with up to nine bridged benzene rings in a row are the longest structurally perfect cyclophane sequences known to date. The synthetic strategy comprises three steps: ester reduction to a tetrakis(hydroxymethyl) compound, derivatisation to the corresponding tetrakis(bromomethyl) derivative, and double cyclisation with the new key building block 14, which was especially developed for this sequence. Single-crystal X-ray analyses (3 a-7 a) and 1H NMR spectroscopy (3-10) show that, regardless of their length, these molecules adopt zigzag folded all-syn conformations. π-Stacks of nanometre dimensions are thus formed.
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  • 84
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    Chemistry - A European Journal 2 (1996), S. 869-876 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; silaguanidinium cations ; silylium cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantium mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH2)3+ (1) and derivatives thereof. The equilibrium structure 1a has D3 symmetry with planar amino groups rotated out of the SiN3 plane by 19.60. The Si-N bond length of 1 a (1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation 1 a by the amino groups (63.5 kcal mol-1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol-1), but 1 a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6- 31 G(d) is markedly lower for Si(NH2)3-(H2O)+ (6) (28.8 kcal mol-1) than for SiMe3(H2O)+ (40.6 kcal mol-1). The tris(dimethylamino) silylium cation Si(N-Me2)3+ (8) is even more stable than 1 a. The complexation energy of Si(NMe2)3-(H2O)+ (10) is only 17.3 kcal mol-1. IGLO calculations of the 29Si N M R chemical shifts predict that 1 a and 8 should not show the same extremely low shielding that is calculated for alkyl-sub-stituted silylium ions. The calculated 29Si resonances for 8 are in reasonable agreement with the experimental N M R spectrum of (Me2N)3 SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation 12 would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of 12 has tert-butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.
    Additional Material: 3 Ill.
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  • 85
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    Chemistry - A European Journal 2 (1996), S. 894-900 
    ISSN: 0947-6539
    Keywords: aza-Claisen rearrangement ; azoniones ; indolizidinones ; ring contractions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The zwitterionic aza-Claisen rearrangement of optically active 3-pyrrolidine acryl esters and various acid chlorides to generate optically active azoninones proceeds with high simple diastereoselectivity (internal asymmetric induction) and a complete 1,3-chirality transfer. The reaction path observed depends on the subsitution pattern of the allylic system: while the more electron-rich alkylated allyl amine fromed predominantly von Braun type products, the α,β-unsaturated esters could be rearranged with high yields. The azoniones thus obtained were treated with electrophiles, inducing regio- and diastereoselective transannular ring contractions. The resulting indolizidinones should be useful key intermediates in alkaloid synthesis.
    Additional Material: 1 Tab.
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  • 86
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    Chemistry - A European Journal 2 (1996), S. 1014-1023 
    ISSN: 0947-6539
    Keywords: alkoxy radicals ; cyclizations ; pyridinethiones ; radicals ; tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of hitherto unknown N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (6) were prepared from substituted pent-4-enyl tosylates or benzylic chlorides. On irradiation with incandescent light heterocycles 6 liberated alkoxy radicals 2, which were studied for rearrangement reactions. Surprisingly, all transformations involving the 1-phenylpent-4-enyl-1-oxy radical (2a), for example, to give the substituted thioether 8, 2-bro-momethyl-5-phenyltetrahydrofuran (11), or the tetrahydrofuran 14a, were not stereoselective. On the other hand 2-, 3- mono-, and 1,5-disubstituted pent-4-enyl-1-oxy radicals 2d-e and 2g cyclized in good yields and with good to excellent stereoselectivities to give the corresponding 2,4-cis- and 2,3-trans-phenyltetra-hydrofurfuryl radicals 3d-e, and the trans-2-benzyl-5-methyl substituted intermediate 3g. The major reaction mode of the 4-phenylpent-4-enyl-1-oxy radical (2f) was the 6-endo cyclization, which afforded 3-phenyltetrahydropyran (13f) as the major product (endo:exo = 93:7) after trapping with hydrogen donors. According to the experimental data of the present study, the unusual reactivity of the 1-phenylpent-4-enyl-1-oxy radical (2a) in 5-exo-trig ring closures could be caused by a coplanar arrangement of the benzyloxy moiety in the transition state of the cyclization. This interaction would lock the radical center in 2a in a preferred conformation, which would result in similar steric effects for both cis- and trans- cyclizations.
    Additional Material: 1 Ill.
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  • 87
    ISSN: 0947-6539
    Keywords: ab initio calculations ; iron oxide ; iron sulfide ; mass spectrometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-transfer behavior of the binary iron chalcogenides FeO and FeS has been examined by means of mass spectrometry and ab initio calculations using the averaged coupled-pair functional (ACPF) method. The experimental and theoretical results are in good agreement with each other and also with previous studies. The ionization energies (IE) of the diatomic species are found to be IE(FeO) = 8.8±0.2 eV, IE(FeO+) = 17.9±0.4 eV, IE(FeS) = 8.3±0.3 eV, and IE(FeS+) = 16.3±0.5 eV. Two new diatomic dications, FeS2+ and FeO2+, are shown to exist as metastable minima on the corresponding potential-energy surfaces. The data enable an evaluation of the intrinsic gas-phase redox properties of FeS and FeO, and the comparison demonstrates that iron sulfide is more prone to undergo facile reduction and oxidation than iron oxide.
    Additional Material: 3 Ill.
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  • 88
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    Chemistry - A European Journal 2 (1996), S. 1251-1257 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; benzenes ; electrophilic substitutions ; proton affinities ; QSAR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An additivity rule for proton affinities (PAS) in polysubstituted benzenes is derived from the MP2(fc)/6-31 G**//HF/6-31 G* + ZPE(HF/6-31 G*) theoretical model by use of the concepts of homodesmic reactions and independent substituents. The performance of the additivity rule of thumb is very good; this is evidenced by the excellent agreement of the estimated PAS with the latest experimental data. We believe that the additivity should work for larger aromatic compounds too. The PA increments, which characterize the influence of each substituent on a particular site of the benzene ring undergoing electrophilic substitution, proved useful in discussing various chemical properties of this family of compounds.
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  • 89
    ISSN: 0947-6539
    Keywords: borazine ; boron nitride ; materials science ; thin films ; titanium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the first time, solid-gas reaction techniques have been used for the synthesis and processing of thin films of boron nitride. Clear to intensely colored blue BN films were grown on Si(100) substrates by the transformation of borazine (B3N3H6) with a titanium complex as initiator under flowing nitrogen gas. The thickness of the films ranged from 70 to 100 nm, as determined by Rutherford backscattering (RBS) and atomic force microscopy (AFM) analyses. The intensity of the blue color of the thin film can be correlated to its thickness. The composition of the film determined by RBS studies corresponds to the stoichiometric formula B0.49N0.45O0.06, and N/B and O/B ratios are found to be 0.92 and 0.12, respectively. Nitrogen contents determined by nuclear reaction analysis agree well with the RBS results. Moreover, Auger electron spectroscopy (AES) measurements show that no titanium is present in the films and confirm the composition determined by RBS studies. X-ray photoelectron spectroscopy (XPS) shows the presence of boron and nitrogen in the blue BN film. Electron spin resonance (ESR) experiments at 293 and 12 K indicate a single broad signal with a g value (g = 2.005) close to that of a free electron. This synthetic approach provides opportunities for the preparation of new thin-film materials and for the fundamental study of solid-gas reactions.
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  • 90
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    Chemistry - A European Journal 2 (1996), S. 1292-1302 
    ISSN: 0947-6539
    Keywords: complexes with nitrogen ligands ; ruthenium complexes ; self-assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of mono- and dimetallic complexes of rack type containing a dinucleating bis-tridentate ligand and RuII-2,2′:6′,2′-terpyridyl (tpy) sites were synthesised and characterised. The 1H NMR spectra of the dimetallic complexes were correlated to structural features, and the crystal structures of the dimetallic complexes were determined. They provide information about the way in which the central substitutent affects the overall shape of the racks and the relative disposition of the metal centres, measured by the pinching angle of the bis-tridentate ligand and the convergence angle of the ancillary tpy units. The latter demonstrates that a CH3 group yields the least bent complex and indicates how parallel the tpy units are. The dimetallic racks exhibit metal-metal interactions mediated by the bis-tridentate ligands as indicated by electrochemical and spectroscopic methods. The bridging-ligand π* orbital and the dπ metal orbital are stabilised by complexation of a second metal. The results obtained provide guidelines for the design of extended racks bearing several metal centres in a linear arrangement, which also represent potential components of molecular electronic devices.
    Additional Material: 14 Ill.
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  • 91
    ISSN: 0947-6539
    Keywords: half-sandwich complexes ; peptide syntheses ; peptides ; rhodium complexes ; ruthenium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic dipeptide ester complexes of the general formula [(L)M(Cl)(K2-NH2CH2CONCH2CO2R)] (1: L=Cp*, M=Rh, 2: L=Cp*, M=Ir, 3: L=η6-C6Me6, M=Ru) react smoothly with various α-L-amino acid esters in the presence of NEt3 to yield the tripeptide ester complexes [(L)M(Cl)(K2-NH2CHR'CONCH2CONHCH2CO2R)] (5-7). In the same fashion chloro K2-tetrapeptide ester complexes 10 and 11 are obtained either from tripeptide ester complexes or by subsequent addition of two equivalents of amino acid ester to a dipeptide ester complex. When the strong base NaOMe is used in the reaction of the diglycine ester compounds with amino acid esters. K3-tripeptide ester complexes 12 and 13 are produced, in which one of the two coordinated peptide nitrogen atoms is pyramidal. The hexamethylbenzene ruthenium complexes 13 with tripeptide ligands are formed with very high diastereoselectivity. A plausible reaction mechanism for the metal-promoted peptide synthesis is presented. Synthesis and isolation of the peptide esters proceeds without racemization.
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  • 92
    ISSN: 0947-6539
    Keywords: additions ; fullerenes ; regioselectivity ; semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three series of regioisomeric bisadducts of C60, namely, C62(anisyl)4 and the mixed systems C62(anisyl)2-(COOEt)2, and C61(COOEt)2(NCOOEt), were synthesized starting from the 1,2-monoadducts C61(COOEt)2 (1), C61-(anisyl)2 (2), and C60(NCOOEt) (4) by using the Bingel and Bamford-Stevens reactions, and nitrene additions. In the case of C61(COOEt)2(NCOOEt) the complete series of nine possible regioisomers were isolated for the first time. For steric reasons the cis-1 isomers of C62(anisyl)4 and C62(anisyl)2(COOEt)2 were not formed. The transannular [6,6] bonds in the cis-1 isomer 42 of C61(COOEt)2(NCOOEt) are closed. The properties and regioselectivities of formation of these bisadducts and their monoadduct precursors were compared with those of the series C62-(COOEt)4 and C60(NCOOEt)2, which we synthesized previously. In the additions to 1, 2, and 4 the preferred positions of attack are e and trans-3 for sterically demanding addends (e.g., combinations of C(anisyl)2 and C(COOEt)2) and cis-1, e, and trans-3 for sterically less demanding addends (e.g., combinations of N(COOEt) and C(COOEt)2). A detailed analysis of the MO structures, the experimental and calculated geometries of monoadduct precursors, and the stabilities of reaction products leads to the conclusion that the addend-independent cage distortion itself is responsible for the observed regioselectivities of bisadduct formations.
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  • 93
    ISSN: 0947-6539
    Keywords: copper proteins ; cross-reactions ; electron-transfer reactions ; kinetics ; metalloproteins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron self-exchange rate constant for the Type 1 blue copper protein umecyanin from horseradish roots has been determined as 6.1 × 103 M-1 S-1 at pH 7.5, I = 0.100 M, 25°C by an NMR line-broadening method. The value obtained is one of the lower self-exchange rate constants determined for this class of protein; this is attributed to the presence of positively charged residues near to the electron-transfer site. The self-exchange rate constants calculated by means of a Marcus analysis of data for the cross-reactions (25°C) of umecyanin with azurin and cytochrome c551 (both from Pseudomonas aeruginosa) are substantially less at 8.0M-1 S-1 and 13.9M-1S-1, respectively, and are independent of pH in the range 7.0-8.0, I = 0.100M. The discrepancy between the self-exchange rate constants obtained by these two different methods can be rationalised if it is assumed that umecyanin reacts with the two proteins employed in the cross-reaction studies through the same site, but that this site is different from that used for the self-exchange process. A comparison of the primary structure of umecyanin with those of other Type 1 copper proteins has revealed that a glutamine rather than a methionine is likely as the fourth ligand of Cu at the active site. Other comparisons are made with stellacyanin, and the electron-transfer reactivity of the two proteins is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 94
    ISSN: 0947-6539
    Keywords: kinetics ; metal-metal bonds ; molybdenum complexes ; multiple bonds ; tungsten complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between diarylthiones and [Mo2(OCH2tBu)6] in hydrocarbon solvents yielded [Mo2(OCH2tBu)6-(μ-S)(=CAr2)] by cleavage of the C=S double bond. The Lewis base adduct [Mo2 (OCH2tBu)6(μ-S) (=CPh2) (PMe3)] (2) has been crystallographically characterized; it contains six- and five-coordinate Mo atoms linked through μ-S and μ-OR groups. The rate of the cleavage of the C=S bond has been studied by variable-temperature 1H NMR in [D8]toluene. A Hammett plot shows that both electron-donating and electron-releasing substituents in the aryl groups enhance the rate relative to Ph2C=S. The activation parameters for cleavage of the C=S bonds in Ph2C=S, (p-MeOC6H4)2C=S, and (m-CF3C6H4)2C=S exhibit essentially identical values for ΔS
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 95
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1552-1555 
    ISSN: 0947-6539
    Keywords: block copolymers ; micelles ; mineralization ; nanostructures ; thin films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Controlled mineralization of gold nanoparticles has been performed in a microemulsion of polystyrene-block-poly(2-vinylpyridine). The starting point was the formation of a thermodynamically stable dispersion of HAuCl4 in inverse micelles of the block copolymer in toluene, which became metastable when the gold was reduced. Kinetic control of the transformation allowed the following stages of the mineralization/coagulation process to be stabilized: 1) one gold particle per micelle, 2) aggregated micelles containing two or three gold particles, and 3) a state in which empty micelles coexist with larger polymer-stabilized gold particles. Distinctive variations in the spectra were observed depending on the particle size and whether two particles had formed a couple with orientation-dependent dipolar interactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 96
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1566-1571 
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric syntheses ; carbolines ; chiral auxiliaries ; Pictet-Spengler reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic and aliphatic Schiff bases of tryptamine react with Fmoc- or phthaloyl-protected amino acid chlorides to form N-acyliminium intermediates, which, in the presence of titanium alkoxides at room temperature, undergo Pictet-Spengler reactions to give tetrahydro-β-carbolines with diastereomeric ratios of up to 99:1. The chiral auxiliary can be removed from the Pictet-Spengler adducts by means of a simple reduction. To rationalize the observed stereoselectivity a transition-state model is proposed in which the titanium atom coordinates both the carbonyl group of the N-acyliminium ion and the amino acid protecting group.
    Additional Material: 2 Tab.
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  • 97
    ISSN: 0947-6539
    Keywords: density functional calculations ; IR spectroscopy ; ruthenium complexes ; time-resolved spectroscopy ; UV ; vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical properties of the metal-metal bonded complexes [Ru-(E)(E′)(CO)2(iPr-DAB)] (E=Cl, E′=SnPh3, PbPh3; E=Me, E′=SnPh3, PbPh3; E=SnPh3, E′=SnMe3, SnPh3, GePh3; E=PbPh3, E′=PbMe3, PbPh3, GePh3; iPr-DAB=N,N'-diisopropyl-1,4-diaza-1,3-butadiene) have been studied. According to time-resolved emission, UV/vis and IR spectra, combined with density functional (DFT) MO calculations, the lowest excited state has triplet metal-to-ligand charge-transfer (3MLCT), triplet halide-to-ligand charge-transfer (3XLCT) or 3σ(E-Ru-E)π* character, depending on the nature and combination of the ligands E and E′. The 3σ(E-Ru-E′)π* state is a bound state whose lifetime is strongly influenced by the ligands E and E′. An exceptionally long lifetime (264 μs at 80 K) is observed for the 3σ(Sn-Ru-Sn)π* state of the symmetrically substituted [Ru(SnPh3)2(CO)2(iPr-DAB)] complex. The reason for this long lifetime is the fact that the excited state of this complex is hardly distorted with respect to the ground state, owing to the delocalised character of the σ(Sn-Ru-Sn) bonding orbital, which mixes strongly with the π* orbital of the iPr-DAB ligand. This delocalisation is also responsible for the unusually high oscillator strength of the σ → π* electronic transition in the visible spectral region.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 98
    ISSN: 0947-6539
    Keywords: antithrombotics ; enzyme inhibitors ; oligonucleotides ; oligosaccharides ; protecting groups ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Derivatization of the octadecathymidylate derivative 18 (T18 ODN) containing a free amine function with sulfo-SIAB® gave the corresponding iodoacetyl ODN 21. Conjugation of the latter with the thiol-containing pentasaccharide 17c gave pentasaccharide-ODN conjugate III, which exhibited anti-Xa and antithrombin activities of 173 U mg-1 and 5 U mg-1, respectively.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1585-1595 
    ISSN: 0947-6539
    Keywords: concave hydrocarbons ; cyclophanes ; host/guest chemistry ; ion-selective electrodes ; prismands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concave hydrocarbons, such as 1 (C36H36), 4 (C60H60), 5 (C54H48), and 6 (C60H52), represent three-dimensionally clamped analogues of π-prismands. They encapsulate small metal ions and accomplish metal-ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion-selective electrodes. The synthetic route is based on well-established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.
    Additional Material: 11 Ill.
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 139-148 
    ISSN: 0947-6539
    Keywords: asymmetric ; syntheses ; Diels-Alder reactions ; dihydropyrans ; Lewis acids ; oxabutadienes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereodivergent asymmetric hetero-Diels-Alder reaction of achiral and chiral 1-oxa-1,3-butadienes carrying an oxazolidine moiety with various enol ethers in the presence of different Lewis acids is described as a highly stereoselective and efficient approach to dihydropyrans, which can be used for the synthesis of carbohydrates. In the cycloaddition of the achiral oxabutadiene very good endo/exo selectivity was possible, and with the chiral oxabutadienes excellent 1,6-asymmetric induction was additionally observed. In the processes a reversal of facial selectivity occurs by changing the Lewis acid, allowing the synthesis of both enantiomers of the dihydropyrans with the same auxiliary. Thus, cycloaddition of 1 to 2 in the presence of Me2 AlCl gives predominantly the endo product 3 (3:4 = 10:1), whereas with SnCl4 the exo product 4 is obtained (3:4 = 1:15). The reaction of 7 and 1 a in the presence of Me2AlCl as promoter nearly exclusively yields the endo-I adduct 16 a (16 a+17 a:18 a+19 a = 〉 50:1; 16 a:17 a = 60:1), whereas with TMS-OTf the endo-II-product 17 a was obtained as the main component (16 a+17 a:18 a+19 a = 〉 50:1; 16 a:17 a = 1:7.9). The use of SnCl4 leads to a mixture of endo and exo, again, however, with excellent induced selectivity. A similarly good induction was obtained with the oxabutadiene 9 containing the new auxiliary 8. Also, other enol others 1 b-g were used, some of which afforded excellent induction. Mechanistic considerations are used to explain the results.
    Additional Material: 4 Tab.
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