Electronic, infrared, and resonance-Raman spectroscopic studies of the linear-chain, halogen-bridged, mixed-valence complexes [Pt(NH3)4][Pt(NH3)4X2]Y4(X = Br or I, Y = HSO4, ClO4, or BF4). The X-ray crystal structures of [Pt(NH3)4][Pt(NH3)4Br2][HSO4]4and [Pt(NH3)4][Pt(NH3)4I2][HSO4]3[OH]·H2O

Abstract

The complexes [Pt(NH3)4][Pt(NH3)4Br2]Y4, Y = HSO4, ClO4, or BF4, and [Pt(NH3)4][Pt(NH3)4I2][HSO4]3[OH]·H2O have been prepared by partial aerial oxidation of Magnus green in 50% H2SO4 in the presence of KBr or KI as appropriate. The complexes are deeply coloured and highly dichroic, as is typical of linear-chain, halogen-bridged species. The crystal structures of the two [HSO4]– salts have been refined within the space groups P21/c(Z= 1) for the bromide and Pmcn(Z=4) for the iodide to final R factors of 0.0373 and 0.0484, respectively. In the case of the bromide, the [PtII(NH3)4][PtIV(NH3)4Br2] chains are longitudinally disordered so that all the Pt atom sites comprise ½PtII+½PtIV and the axial bromine atoms half-occupy two positions 0.559 A apart; the key bond lengths are PtIV–Br 2.467 A, and PtII–Br 3.022 A. The PtIIN4 and PtIVN4 square planes are eclipsed when viewed down the chain axis. In the case of the iodide, the [PtII(NH3)4][PtIV(NH3)4I2] chains are completely ordered, with the bridging iodine atoms occupying only one site; the PtIV–I and PtII–I distances are 2.686 and 3.148 A, respectively. The PtIIN4 and PtIVN4 square planes are, in this case, staggered by 46° when viewed down the chain axis. The intense resonance-Raman spectra of the complexes, obtained by irradiating within the contours of their PtIVâ†� PtII intervalence bands, are dominated by progressions (at most to 14 members) in the axial, totally symmetric, chain-stretching mode, ν1, νsym(X–PtIV–X), as shown by polarisation and intensity studies. The results are discussed with respect to related ones for other localised mixed-valence complexes.