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  • Chemistry  (17)
  • lanthanides  (2)
  • self-assembly  (2)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 323-337 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution chemistry of Cu(II) with a series of five planar tridentate nitrogen ligands, 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy, 1), 2,6-bis(l-methylbenzimidazol-2-yl)pyridine (mbzimpy, 2) 2,6-bis(benzothiazol-2-yl) pyridine (bzthpy, 3), 2,6-bis(benzoxazol-2-yl)pyridine (bzoxpy, 4), and 2,2′, 6′, 2″-terpyridyl (terpy, 5) is reported. Electronic and EPR spectra are consistent with the complexes [CuL]2+ having essentially tetragonal structure in solution, with the fourth coordination site in the plane of the ligand occupied by solvent. bzthpy and bzoxpy show smaller ligand-field splittings than bzimpy, mbzimpy, and terpy, and are easily decomplexed from the copper. Substitution of the coordinated solvent molecule in the plane of the ligand is observed with Cl- and OH- (provided that the ligand has no acidic protons) for all ligands except terpy. The reaction between [Cu(mbzimpy)]2+ and imidazole has been studied by potentiometric titration in MeCN/H2O 1:1 and shows strong binding of the imidazole in the plane (log K = 4.5 at 25°), and also the formation of an imidazolate-bridged dinuclear species.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient combination of electrospray mass spectrometry (ES-MS), spectrophotometric and 1H-NMR titrations in solution is used to characterize the assembly of the segmental ligand 2-{6-[1-(3,5-dimethoxybenzyl)-1H-benzimidazol-2-yl]pyridin-2-yl}-1, 1′-dimethyl-5,5′-methylene-2′-(5-methylpyridin-2-yl)bis[1H- benzimidazole] (L2) with ZnII and 4f metal ions, LnIII. Ligand L2 reacts with Zn(ClO4)2 in MeCN to give successively [Zn(L2)2]2+, where the metal ion is coordinated by the tridentate binding units of the ligands, and the double-helical head-to-head complex [Zn2(L2)2]4+. When L2 reacts with Ln(ClO4)3 (Ln = La, Eu, Lu), LaIII only leads to a well-defined cylindrical C1-symmetrical homodinuclear head-to-tail complex [La2(L2)3]6+ in solution, while chemical-exchange processes prevent the 1H-NMR characterization of [Eu2(L2)3]6+, and LuIII gives complicated mixtures of complexes. However, stoichiometric amounts of LnIII (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Y, Lu), ZnII, and L2 in a 1:1:3 ratio lead to the selective formation of the C3-symmetrical heterodinuclear complexes [LnZn(L2)3]5+ under thermodynamic control. Detailed NOE studies show that the ligands are wrapped about the C3 axis defined by the metal ions, and the separation of dipolar and contact contributions to the 1H-NMR paramagnetic shifts of the axial complexes [LnZn(L2)3]5+ (Ln = Ce, Pr, Nd, Sm, Eu) in MeCN establishes that ZnII occupies the pseudo-octahedral capping coordination site defined by the three bidentate binding units, while LnIII lies in the resulting ‘facial’ pseudo-tricapped trigonal prismatic site produced by the three remaining tridentate units. Photophysical measurements show that [LnZn(L2)3]5+ (Ln = Eu, Tb) are only weakly luminescent because of quenching processes associated with the C3-cylindrical structure of the complexes. The use of 3d metal ions to control and design isomerically pure ‘facial’ tricapped trigonal prismatic lanthanide building blocks is discussed together with the calculation of a new nephelauxetic parameter associated with heterocyclic N-atoms coordinated to LnIII.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 548-557 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stability constants have been measured for a series of ligands based on a 2,2′-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms dinuclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordinate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the complexes depend strongly on the solvent, and in MeCN, which is a good solvent for copper(I), the complexes are less stable and assemble in a stepwise manner. The interconversion of the enantiomers may be followed by 1H-NMR and takes place on a millisecond time scale around room temperature. The trends in lability are similar to those found for the stability of the complexes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The para-substituted tridentate ligands 2,6-bis[1-(3,5-dimethoxybenzyl)benzimidazol-2-yl]-4′-X-phenyl)-pyridine (X = H: L3; X = NO2: L4; X = NEt2: L5) have been synthesized in six steps using Kröhnke reactions. Spectroscopic results show that the electronic properties of the ligands are strongly influenced by the nature of the substituent bound to the pyridine ring and extended Hückel calculations performed on 4-(X-phenyl)pyridine fragments give a qualitative insight into the factors responsible for the striking differences observed in the absorption spectra. Upon complexation to FeII, the ligands L2-L5 give intensely coloured pseudo-ocatahedral low spin [Fe(Ln)2]2+ (n = 2-5) complexes in acetonitrile solution. Electrochemical and spectroscopic measurements show that the particular electronic characteristics associated with each substituent strongly influence the properties of the resulting FeII complexes as demonstrated by the very intense MLCT transition (∊ 〉 50000 M-1 cm-1) observed in the green complex [Fe(L5)2]2+.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1759-1766 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Electrospray Mass Spectrometry (ES-MS) of eight different supramolecular complexes shows that the molecular peaks of the desolvated multiply charged cations can be recorded more easily than by Fast-Atom-Bom-bardment Mass Spectrometry (FAB-MS) measurements of similar compound. The preliminary application of the ES-MS technique to self-assembled helical complexes obtained from ligands L3 to L8 with various metal ions (Cu, Co, Eu, Tb) indicates that ES mass spectra qualitatively reflect the species present MeCN solution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 931-942 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of a modified Phillips reaction allows the synthesis of complicated heteroleptic ligands based on pyridine and 1H-benzimidazole moieties. The key-step formation of aromatic 1H-benzimidazole rings from N-(2-nitroaryl)arenecarboxamides significantly improves the possibilities of the classical intermolecular Phillips reactions and can be applied to the synthesis of large oligo-multidentate units. Segmental heteroleptic ligands containing two different bidentate coordinating units (see 14) or bidentate and terdentate sites connected by ‘diphenylmethane’ ( = methylenebis(phenylene)) spacers (see 15 and 16) were obtained in fair to good yield by using multistep syntheses following this strategy. Heterotrileptic ligands (bidentate-terdentate-bidentate, see 19 and 20; terdentate-terdentate-terdentate, see 23) requiring the simultaneous formation of four 1H-benzimidazole rings in one step were prepared and demonstrate the extended possibilities of this methodology. Data are presented to show that the milder conditions used for this modified Phillips reaction together with its flexibility are essential for the development of ligands adapted for the self-assembly of heteronuclear helical complexes.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (mbzimpy, 1) reacts with EuIII to give [Eu(mbzimpy)(NO3)3(CH3OH)] [4] whose crystal structure (EuC22H21N8O10, a = 7.658(3) Å, b = 19.136(2) Å, c = 8.882 Å, β = 104.07(1)°, monoclinic, P21, Z = 2) shows a mononuclear structure where EuIII is ten-coordinate by a meridional tridentate mbzimpy ligand, three bidentate nitrates, and one CH3OH molecule, leading to a low-symmetry coordination sphere around the metalion. Essentially the same coordination is found in the crystal structure of [Eu(obzimpy)(NO3)3] (8) (EuC35H45N8O9, a = 9.095(2) Å, b = 16.624(2) Å, c = 26.198(6) Å, β = 95.85(1)°, monoclinic, P21/c, Z = 4) obtained by reaction of 2,6-bis(1-octylbenzimidazol-2-yl)pyridine (obzimpy, 2) with EuIII. Detailed photophysical studies of crystalline [Ln(mbzimpy)(NO3)3(CH3OH)] and [Ln(obzimpy)(NO3)3] complexes (Ln = Eu, Gd, Tb, Lu) show that 1 and 2 display 1ππ* and 3ππ* excited states very similar to those observed in 2,2′:6′,2″-terpyridine, leading to efficient ligand to LnIII intramolecular energy transfer. Spectroscopic results show that an extremely efficient mbzimpy-to-EuIII transfer occurs in [Ln(mbzimpy)(NO3)3(CH3OH)] and in the case of TbIII, a TbIII-to-mbzimpy back transfer is also implied in the deactivation process. The origin of these peculiar effects and the influence of ligand design by going from mbzimpy to obzimpy are discussed. 1H-NMR and luminescence data indicate that the structure found in the crystal is essentially maintained in solution.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general strategy for the synthesis of oligobipyridine ligands 2-5 containing from two to five 2,2′-bipyridine subunits, for helical metal complexes is described (sec Scheme). Both the unsubstituted parent strands (a series) as well as their derivatives bearing fester or amide functions in the 4,4′-positions of the bipyridine moieties (b-d series) have been obtained.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fe(ClO4)2 reacts with the segmental ligand 2-{6-[1-(3,5-dimethoxybenzyl)-1H-benzimidazol-2-yl]pyridin-2-yl}-1,1′-dimethyl-5,5′-methylene-2′-(5-methylpyridin-2-yl)bis[1H-benzimidazole] (L2) in MeCN to give the diamagnetic deep violet complex [Fe(L2)2]2+ where the metal is pseudo-octahedrally coordinated by two perpendicular tridentate binding units. When L2 reacts with an equimolar mixture of Ln(ClO4)3 (Ln = La, Ce, Pr, Nd, Sm, Eu) and Fe(ClO4)2, electrospray-mass spectrometric, spectrophotometric, and 1H-NMR data in MeCN show the selective formation of the deep red heterodinuclear C3-cylindrical complexes [LnFe(L2)3]5+ where the three ligands L2 are wrapped about the metal-metal axis. FeII occupies the pseudo-octahedral capping site produced by the three bidentate units and LnIII lies in the resulting ‘facial’ pseudo-tricapped trigonal prismatic site defined by the three remaining tridentate coordinating units. The heterodinuclear complexes [LnFe(L2)3]5+ display spin-state equilibrium (1A ⇄ 5T) and thermochromism in MeCN between 243 and 333 K. Detailed 1H-NMR, UV/VIS, and magnetic measurements in solution show that the partial spin-crossover behavior of [LnFe(L2)3]5+ occurs for Ln = La—Eu with similar thermodynamic parameters (ΔHsc = 20-23 kJ·mol-1 and ΔSsc = 55-66 J·mol-1·K-1) indicating that the size of LnIII has a negligible influence on the spin-state equilibrium. However, the smaller LnIII ions have less affinity for the pseudo-tricapped trigonal prismatic coordination site in the heterodinuclear complexes as demonstrated by the partial decomplexation of [YFe(L2)3]5+ to give [Fe(L2)2]2+ and the absence of the heterodinuclear complex [LuFe(L2)3]5+ under the same conditions. The crucial role played by the sterically demanding FeII in the assembly processes is discussed together with the use of the efficient combination of lanthanide probes with magnetic d-block probes for the design and investigation of luminescent and magnetic materials with controlled structural and physical properties. Photophysical measurements reveal that efficient ligand → metal and Eu → Fe energy transfer occur in [EuFe(L2)3]5+ which strongly quench both the ligand and the Eu-centered luminescence.
    Additional Material: 8 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 361-391 
    ISSN: 1573-1111
    Keywords: helicate ; supramolecular ; self-assembly ; device ; catenate ; cage ; cluster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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