Study of Mixed-Valence State in Halogen-Bridged Mixed-Valence Platinum(II,IV) Complexes by Temperature Dependence of Intervalence Charge-Transfer Spectra

Abstract

Abstract The low-energy absorption edge due to the intervalence charge-transfer (IVCT) transition from PtII to PtIV has been investigated at 4.2 K and room temperature in single crystals of [Pt(en)2][PtBr2(en)2]Y4 {Y=ClO4(PBC), HSO4(PBHS)}, [Pt(en)2][PtI2(en)2](HSO4)4·4H2O (PIHS) and [Pt(en)2][PtX2(en)2](SO4)2·6H2O {X=Cl(PCSW), Br(PBSW), I(PISW)}. The IVCT absorption edges in PCSW, PBSW, and PISW shifted to the lower-energy side (i.e. red shift), while those in PBC, PBHS, and PIHS shifted to the higher-energy side (i.e. blue shift) with an increase in temperature. We consider that the thermal effect of the valence fluctuation of the Pt mixed-valence state causes a red shift of the IVCT absorption edge and that the thermal effect of the hydrogen bond between the PtII complex ion and the PtIV complex ion causes a blue shift of the IVCT absorption edge. These two effects coexist and compete with each other in one complex. The dominant effect of the two effects determines the direction of the shift of the IVCT absorption edge, namely, the temperature dependence of the Pt mixed-valence state.