Valence Structure in One-Dimensional Binuclear Complexes, A_4[Pt_2X(P_2O_5H_2)_4]・nH_2O(A: K, NH_4, Cs; X: Cl, Br, I), Studied by Nuclear Magnetic Resonance

^<31>P MAS NMR spectra were measured on -X-Pt-Pt-X-Pt-Pt-X- type complexes, A_4[Pt_2X(P_2O_5H_2)_4]・nH_2O(A: K, NH_4, Cs; X: Cl, Br, I). In these complexes, two kinds of ^<31>P resonance lines observed at δ=50-70 and 20-40ppm, whose values are close to those in the monomer Pt^<2+> and Pt^<3+> complexes, respectively. From the analyses of spectra and spin-lattice relaxation times T_1, a mixed-valence -X-Pt^<2+>-Pt^<2+>-X-Pt^<3+>-Pt^<3+>-X- structure was concluded for K_4[Pt_2Cl(P_2O_5H_2)_4]・nH_2O, (NH_4)_4[Pt_2X(P_2O_5H_2)_4]・nH_2O and Cs_4[Pt_2X(P_2O_5H_2)_4].