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  • 1
    ISSN: 1434-1948
    Keywords: 2,2′-Bipyridines ; Chelate complexes ; Hydrogen bonding ; π-π stacking ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal-ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine-metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π-π stacking of the bipyridine rings.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99078_s.pdf or from the author.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0947-6539
    Keywords: cyclovoltammetry ; electronic effects ; photoelectron spectroscopy ; pyrazole ligands ; Mössbauer spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic effect of substituting CH with N in poly(pyrazolyl)-borato ligands and their transition-metal complexes is shown to be a decrease in energy of the filled metal and ligand orbitals. This conclusion is based on the cyclovoltammograms and photoelectron spectra of bis(hydrotris(azolyl)borato)-iron(II) and -cobalt(II) complexes (azolyl = pyrazolyl and 1,2,4-triazolyl) and on MO calculations. 57Fe Mössbauer spectra of bis(hydrotris(1,2,4-triazolyl)-borato)iron(II) show that there is a fine-tuning of the HOMO-LUMO gap by a shift in transition temperature for the spin equilibrium. 15N NMR spectroscopy supports the assignment of a higher negative charge to the exodentate N-4 nitrogen than to the endodentate N-2 or N-3 positions in the poly(azolyl)borato anions, where azolyl is 1,2,4-triazolyl or tetrazolyl. The electron withdrawing effect of the additional nitrogen atoms and the in-corporation of water of crystallization by O-H ⃛ N bonding both assist in the formation of (azolyl)C-H ⃛ O bonds.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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