The effects of the in-plane ligand, the metal atom, the bridging halogen atom and the counter-anion on the electronic structures of a series of linear-chain, halogen-bridged, mixed-valence complexes of platinum and palladium have been investigated. Complexes of the type [ML][MLX2]Y 4, where M = Pd or Pt, X = Cl, Br or I, L = 3, 7-diazanonane-1,9- diamine, 4,7-diazadecane-1,10-diamine, 1,4,8,11-tetraazacyclotetradecane or 1,4,8,12-tetraazacyclopentadecane and Y = BF4, ClO4 or PF6, have been examined by means of electronic, Raman and resonance-Raman spectroscopy. The electronic spectra of the complexes each show an intense intervalence charge-transfer band in the visible region, occurring at higher energy, Eg, than it does for analogous bis(ethylenediamine) complexes; this implies greater localisation of valences for the quadridentate than for the bis(ethylenediamine) complexes, in agreement with conclusions drawn from the X-ray structural results. Resonance-Raman spectra of the complexes display long progressions in the symmetric chain stretching mode ν1, νsym(X-MIV-X), corresponding members occurring at higher wavenumbers than for the analogous en complexes. Progressions in ν1 reach at most to ν1 = 12 for X = Cl, ν1 = 9 for X = Br and ν1 = 5 for X = I. Both the trends in Eg and also those in ν1 (max) vary in the order I < Br < Cl, Pd < Pt and BF4 ≤ ClO4 < Pf6, implying increased valence localisation to the right in each series.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - 1991 Dec 1|
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