NEW DONOR-ACCEPTOR SYSTEM BASED ON [PT(NH3)(4)](2-) IONS() AND [W(CN)(8)](3)

A new donor-acceptor system based on [Pt(NH3)(4)](2+) and [W(CN)(8)](3 -) has been characterized in aqueous solution and the solid state by s pectroscopic and electrochemical techniques. In aqueous solution the 1 :1 ion pair {[Pt(NH3)(4)](2+),[W(CN)(8)](3-)} exhibits an outer-sphere metal-to-metal charge-transfer transition at 485 nm (epsilon = 49 +/- 2 dm(3) mol(-1) cm(-1)) with association constant K-A = 26 +/- 3 dm(3 ) mol(-1) at I = 0.45 mol dm(-3) (KNO3) and 298 K. Electrochemical mea surements revealed a [W(CN)(8)](3-/4-) reversible couple at +0.27 V (v s. saturated calomel electrode) in 0.1 mol dm(-3) KNO3 for the novel i on pair. The {[Pt(NH3)(4)](2+),[W(CN)(8)](3-)} system is paramagnetic in aqueous solution (g(iso) = 1.96 at 293 K). The results are interpre ted using Hush theory (coupling parameters alpha(2) = 1.69 x 10(-4) an d H-if = 268 cm(-1), reorganization energy for the optical electron-tr ansfer process chi = 164.6 kJ mol(-1), thermal activation barrier E(th ) = 92.4 kJ mol(-1) and electron-transfer rate constant k(et) = 3.3 x 10(-4) s(-1)) and compared with the corresponding parameters for other [M(CN)(n)](3-/4-) couples. The bimetallic Pt-W system has been isolat ed in the solid state as [Pt(NH3)(4)](2)[W(CN)(8)][NO3]. 2H(2)O. The c omplex is paramagnetic (at 293 K g(iso) = 1.97; at 77 K g(perpendicula r to) = 1.96, g(parallel to) = 1.98).