Syntheses of cyanide bridged-mixed valent complexes with dynamic electronic state

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A cyanide bridged molecular square of [Ru^<II>_2Fe^<II>_2(μ-CN)_4(bpy)_8](PF_6)_4 CHCl_3 H_2O, abbreviated as [Ru^<II>_2Fe^<II>_2](PF_6)_4, was synthesized and electrochemically generated mixed valence states were studied by spectroelectrochemical methods. The complex cation of [Ru^<II>_2Fe^<II>_2]^<4+> is nearly square composed of Ru(II) and Fe(II) ions alternately bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru^<II>_2Fe^<II>_2](PF_6)_4 in acetonitrile showed four quasi-reversible waves at 0.69, 0.94, 1.42, and 1.70 V (vs SSCE), which correspond to the four one-electron redox processes of [Ru^<II>_2Fe^<II>_2]^<4+> 【double arrow】 [Ru^<II>_2Fe^<II>Fe^<III>]^<5+> 【double arrow】 [Ru^<II>_2Fe^<III>_2]^<6+> 【double arrow】 [Ru^<II>Ru^<III>Fe^<III>_2]^<7+> 【double arrow】 [Ru^<III>_2Fe^<III>_2]^<8+>. Electrochemically generated [Ru^<II>_2Fe^<II>Fe^<III>]^<5+> and [Ru^<II>_2Fe^<III>_2]^<6+> showed new absorption bands at 2350 nm (ε= 5500 M^<-1>cm^<-1>) and 1560 nm (ε= 10500 M^<-1>cm^<-1>), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe^<II> to Fe^<III> and from Ru^<II> to Fe^<III> ions, respectively. The electronic interaction matrix elements (H_<AB>) and the degrees of electronic delocalizafcon (α^2) were estimated to be 1090 cm^<-1> and 0.065 for the [Ru^<II>_2Fe^<II>Fe^<III>_2]^<5+> state and 1990 cm^<-1> and 0.065 for the [Ru^<II>_2Fe^<III>_2]^<6+> states.