Effects of Nitrogen Substitution in Poly(Pyrazolyl)Borato Ligands: From Orbital Energy Levels to C–H ⃛ O Hydrogen Bonding
1996; Wiley; Volume: 2; Issue: 8 Linguagem: Inglês
10.1002/chem.19960020815
ISSN1521-3765
AutoresChristoph Janiak, Tobias G. Scharmann, Jennifer C. Green, Richard P. G. Parkin, Mario J. Kolm, Erwin Riedel, Wulfhard Mickler, José Elguero, Rosa M. Charamunt, Dionísia Sanz,
Tópico(s)Metal complexes synthesis and properties
ResumoAbstract 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. 57 Fe 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. 15 N 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.
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