Vibrational Studies of, and Model for, Halogen-Bridged Linear-Chain Mixed-Valence Complexes
A number of complexes of the type [MII(LL)2] [PtIV(LL)2Cl2] [ClO4]4, where M = Ni, Pd or Pt and LL = 1,2-diaminoethane (en) or 1,2-diaminopropane (pn), as well as the monomers [PtIV(LL)2Cl2] Cl2 and [MII(LL)2] Cl2 have been studied using Fourier transform infrared (f.t.i.r.) and resonance Raman spectroscopy. Under conditions of low temperature and moderate resolution (ca. 0.5 cm-1) it has proved possible to observe chlorine isotopic splitting in bands due to both the symmetric and the antisymmetric stretching modes of the linear PtIVCl2 units in the chains. On the basis that the one-dimensional electronic properties of these chains are likely to be related to the in-chain PtIV-Cl stretching force constants, a simple vibrational model is presented, which is able to reproduce the observed splitting patterns to well within experimental error. A comparative study of the PtIV-Cl stretching force constants for the series of en complexes shows the trend: trans-[PtIV (en)2 Cl2] Cl2 (monomer) > PdII-PtIV > NiII-PtIV > PtII-PtIV. This trend is in line with that of the MII-> PtIV intervalence band maxima, namely PdII-PtIV (25 000 cm-1) > NiII-PtIV (22 200 cm-1) > PtII-PtIV (20 800 cm-1), indicating an increase in MIIldots Cl chain interaction (and an expected increase in conductance) along the series.
Philosophical Transactions of the Royal Society of London Series A
- Pub Date:
- May 1985