CONTROLLING THE MIXED-VALENCE STATE OF HALOGEN-BRIDGED ONE-DIMENSIONAL PLATINUM COMPLEXES BY THE SUBSTITUTION OF COUNTER IONS

The mixed-valence states of halogen-bridged one dimensional platinum complexes have been investigated by the substitution of counter ions. The crystal structures of [Pt(en)2][PtCl2(en)2](PF6)4 (Cl-PF6), [Pt(en)2][PtCl2(en)2](HSO4)4 (Cl-HSO4) and [Pt(en)2][PtBr2(en)2](H2PO4)4.6H2O (Br-H2PO4) (en=ethylenediamine) have been determined by single-crystal X-ray diffraction, and their absorption edges have been measured at room temperature. The crystal data are: for Cl-PF6, monoclinic, P2/m, a=9.204(3), b=5.506(2), c=8.185(2)angstrom, 8=107.29(2)-degrees and Z=-1/2; for Cl-HSO4, orthorhombic, Ibam, a=9.261(l), b=14.422(2), c=10.929(1)angstrom, and Z=2; for Br-H2PO4, monoclinic, P2/a, a=19.463(2), b=5.722(l), c=8.325(1)angstrom, beta=101.59(l)-degrees and Z=1. The absorption edegs of the intervalence charge-transfer bands are c.a. 17,500cm-1 for Cl-PF6, c.a. 16,500cm-1 for Cl-HSO4 and c.a. 14,800cm-1 for Br-H2PO4. These results show that the counter ion size and the hydrogen atom of the counter ion influence the mixed-valence state. A mid-gap absorption band below the absorption edge is found at c.a. 14,700cm-1 in Cl-HSO4.