title: Halide ligand-more than just sigma-donors? A structural and spectroscopic study of homologous organonickel complexes.
abstract: The isoleptic organonickel complexes [(bpy)Ni(Mes)X] (bpy ) 2,2'-bipyridine; Mes ) 2,4,6-trimethylphenyl; X ) F,Cl, Br, or I, and for comparison X ) OMe and SCN) have been investigated by multiple spectroscopic means.Their structures have been determined in part by single-crystal X-ray diffraction, the full series by extended X-ray absorption fine structure. The long-wavelength charge transfer absorptions (mainly metal-to-ligand charge transfer)obtain contributions from the mesityl coligand but are almost invariable upon variation of X. UV-vis spectroscopy allowed investigation of the solvolysis reaction [(bpy)Ni(Mes)X] + Solv a [(bpy)Ni(Mes)(Solv)]+ + X-, which occurs very fast for X ) I (k ) 0.176(4) M(-1) s(-1)) or Br but very slow for X ) Cl (k ) 5.18(5) x 10(-5) M(-1) cm(-1))or F. Quantum chemical (density functional theory) calculations on the geometry, electronic states, and electronic transitions (time-dependent density functional theory) are very helpful for detailed insight into the role the X coligands play in these complexes. The combination of methods reveals rather strong, highly covalent Ni-X bonds for all halide coligands but marginal pi-donation.
authors.affiliation: UniVersität zu Köln, Department für Chemie, Bereich Anorganische Chemie, Greinstrasse 6,D-50939 Köln, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Klein
authors.forename: André
authors.initials: A
authors.lastname: Kaiser
authors.forename: Wolfram
authors.initials: W
authors.lastname: Wielandt
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Belaj
authors.forename: Eric
authors.initials: E
authors.lastname: Wendel
authors.forename: Helmut
authors.initials: H
authors.lastname: Bertagnolli
authors.forename: Stanislav
authors.initials: S
authors.lastname: Zális