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  • 1
    Electronic Resource
    Electronic Resource
    The W2Cl4(NHCMe3)2(PR 3)2 molecules (R 3=Me3, Et3, Pr n 3, Me2Ph) I. Their isomeric forms, interconversion proeesses, crystalline forms, and detailed molecular structures (1994)
    Springer
    Journal of cluster science 5 (1994), S. 11-36 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; isomeric forms ; crystal structure ; triple bonds ; interconversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A thorough study of compounds with the formula W2Cl4(NHCMe3)2(PR3)2, withR 3=Me3, Et3, Prg n 3 Me2,Ph, is reported. In addition to the previously reported crystalline compounds, namely Ia,trans-W2Cl4(NHCMe3)2(PMe3)2 in space group Pmmn;3a,trans-W2Cl4(NHCM3)2(PEt3)2 in space group P21/a (or P21/c); and4,cis-W2Cl4(NHCMe3)2(PMe2Ph)2 in Pna21, we have obtained and structurally characterized the following new substances,1b,trans-W2Cl4,(NHCMe3)2(PMe2)2, space group P21/c,a= 12.233 (4) Å,b= 12.872 (4) Å,c=17.095 (5) Å,β=93.52 (2)°,Z=4,V=2687 (1) Å3 2,cis-W2Cl4(NHCMe3)2(PMe3)2, P21/c,a=9.673 (4) Å,b=17.249 (4) Å,c=16.244 (5) Å,β=99.63 (3),Z = 4 ,V=2669 (1) Å.3b,trans-W2Cl4(NHCMe3)2(PEt3)2, Pl,a=16.850 (3) Å,b=17.797 (3) Å,c= 11.459 (2)Å,α= 101.02 (1),β= 103.13°, y=84.23 (1)°,Z=4,V= 3279 (1) Å5,trans-W2Cl4(NHCM3)2(PMe2Ph)2, Fdd2,a=39.563 (8) Å at 20°C; 39.325 (10) Å at -6O°C,b = 57.543 (17) Å at 20°C; 57.186 (16) Å at -60°C,c= 8.810 (1) Å at 20°C; 8.770 (1) Å at - 60°C ,Z=24,V=20057 (7) Å3 (20°C), 19723 (8) Å3 ( - 60°C) .6,trans-W2Cl4(NHCMe3 2(PPrn 3)2, Pl,a= 17.287 (2) Å (20°C); 17.077 (5) Å (-60°C),b= 19.119 (2) Å (20°C); 18.952 (6) Å (-60°C),c= 12.713 (1) Å (20°C); 12.668 (4) Å (-60°C),Z=4,V= 3980 (1) Å3 (20°C), 3898 (2) ,Å3 ( - 60°C). In addition, the structure of3a was re-determined and refined so that the disorder ratio was a refined parameter, leading to a value of 0.520:0.480 instead of being arbitrarily fixed at 0.50:0.50. In all of the structures the molecules are held in eclipsed (but very distorted) rotational conformations and the W-W distances are all within the range of 2.305-2.330 Å. As will be shown in a later paper, for all phosphines, thecis andtrans isomers are of similar stability and an equilibrium mixture exists in solution. It is also shown that1a and3a do not contain unexpectedly short W-N bonds as previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165490
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  • 2
    Electronic Resource
    Electronic Resource
    Mo2(O2CPh)6(PEt3)2, the second example of bridging Y11-02CR for dimolybdenum (III) compounds (1995)
    Springer
    Journal of cluster science 6 (1995), S. 39-59 
    Details
    ISSN: 1572-8862
    Keywords: Carboxylate ; molybdenum ; mixed valence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract From the reaction or Mo2Cl6(THF)3 with excess of NaO2CPh and PEt3 in THF three types of crystals have been obtained and recrystallized in CH2Cl2. They are brown compound Mo2(O2CPh)6(PEt3)2·2CH2Cl2 (1), yellowβ-Mo2(O2CPb)4 (2), and black Mo4O6(O2CPh)6(PEt3)2.CH2Cl2 (3). When a strict ratio of MO2Cl6(THF)3:NaO2CPh = 1:2 was applied, Mo2(O2CPh)4(THF)2, (4) was the only compound separated from the THF reaction mixture. Their structures have been determined by X-ray crystallography. There are three coordination modes of benzoate in 1: bridgingη 2-O2CPh, bridgingη 1-O2CPh and terminal O2CPh groups. Compound 2 is chemically well known, but was found to pack differently from the previously reported structure. Mo4O6(O2CPh)6(PEt3)2·CH2C12 (3) is a mixed-valence Mo (IV, V) tetranuclear compound in a butterfly arrangement. A molecule of 4 is actually a MO2(O2CPh)4 molecule with two THIF molecules axially coordinating to the molybdenum atoms. The crystallographic data for these compounds are as follows: 1, triclinicPl witha = 11.612(3) Å, b = 11.970(2) Å,c=12.135(3) Å,α=95.55(2)°,β=117.51(2)°,γ98.84(2)°,V=l450.8(7) Å3,Z=1,R=0.0673, and R w ,=0.0936; 2, monoclinicP21/n witha = 14,437(2) Å,b=5.6168(7) Å,c=15.979(3) Å,β=93,93(l)°,V=1292.7(4) Å3,Z=2,R=0.0217, and Rw=0.0352; 3, trigonal (hexagonal setting)R3¯ witha=28.83(4) Å,c=44.98(2) Å,V=323570(10) Å3,Z=18,R=0.067, andwR2=0203; 4 monoclinicP21/c witha=9.456(4) Å,b=17.757(8) Å,c=10.887(3) Å,β=109.63(2)°,V=1722(2)Å3 Z=2,R=0.0330, andR w = 0.0451.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01175835
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  • 3
    Electronic Resource
    Electronic Resource
    New synthetic routes for the preparation of the triangular trinuclear clusters of tungsten-containing bromine atoms as terminal ligands: Structural characterization of [W3S4Br3(depe)3]PF6·0.5C7 H8 and [W3S4Br3(depe)3]Br·2CH3OH (1990)
    Springer
    Journal of cluster science 1 (1990), S. 287-305 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; clusters ; preparation ; triangular ; trinuclear
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Synthetic methods are reported for the preparation of compounds containing the trinuclear triangular cluster [W3S4Br3(depe)3[+. These involve reactions between WBr5 and NaB(C2 H5)3H or NaBH4 as reducing agent in THF, and subsequent addition of methanolic solutions of NaHS and depe ligand. Both compounds, [W3S3Br3(depe)3]PF6·0.5C7H8,1, and [W3S4Br3(depe)3]Br·2CH3OH,2, are characterized by x-ray single crystal studies. Compounds1 and2 crystallize in space group $$P\bar 1$$ . For1,a=10.427 (3) Å,b=15.415(4) Å,c=18.140(5) Å, α=79.36(2)°, β=73.59(2)°, γ=81.54(2)°, andV=2734.8(2) Å3;R=0.050 and for 2a=10.491(3) Å,b=15.074(3) Å,c=18.246 Å, α=95.76(2)°, β=105.82(2)°, γ=98.18(2)°, andV=2718.4(3) Å3;R=0.081. The two cations in1 and2 possess C3 symmetry. The W-W distances are in the range 2.783−2.891 Å (for1) and 2.778−2.785 Å (for2) and the average W-Br distances in1 and2 are 2.616[2] Å and 2.594[4] Å, respectively. Each metal atom in the [W3S4Br3(depe)3]+ ions is attached to one capping sulfur atom, two bridging sulfur atoms, one bromine atom, and one chelating depe ligand. One P atom in depe ligand istrans to μ3-S and the otherP atom istrans to a μ2-S atom. UV-Vis and NMR spectra for these compounds are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032274
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  • 4
    Electronic Resource
    Electronic Resource
    Staphylococcal nuclease reviewed: A prototypic study in contemporary enzymology (1979)
    Springer
    Molecular and cellular biochemistry 23 (1979), S. 131-141 
    Details
    ISSN: 1573-4919
    Keywords: Nuclease ; Staphylococcal Nuclease ; Micrococcal Nuclease ; Protein Folding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary This is the last in a series of four articles in which the chemical, enzymological and crystallographic work on Ribonucleate (deoxyribonucleate)-3′-nucleotidohydrolase, EC 3.1.4.4 (staphylococcal nuclease, micrococcal nuclease) will be reviewed and correlated. This article discusses the use of the nuclease as a model system for the study of the mechanisms and energetics of the folding-unfolding reaction in proteins and for the study of the interrelationships between amino acid sequence and three-dimensional structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00219452
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  • 5
    Electronic Resource
    Electronic Resource
    Staphylococcal nuclease reviewed: A Prototypic study in contemporary enzymology. II. Solution studies of the nucleotide binding site and the effects of nucleotide binding. (1979)
    Springer
    Molecular and cellular biochemistry 23 (1979), S. 3-16 
    Details
    ISSN: 1573-4919
    Keywords: Nuclease ; Staphylococcal Nuclease ; Micrococcal Nuclease ; Enzyme Function and Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary This is the second of a series of four articles in which the chemical, enzymological and crystallographic work on Ribonucleate (deoxyribonucleate)-3′-nucleotidohydrolase EC 3.1.4.4 (staphylococcal nuclease, micrococcal nuclease) will be reviewed and correlated. This article discusses studies in solution delineating the extent of the binding site of the enzyme and identifying some of the particular amino acid residues that form this site. In addition, the effects of the very potent inhibitory combination of thymidine-3′,5′-diphosphate and Ca2+ on the conformation of the enzyme and its physical, chemical and enzymological properties will be reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226675
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