Spectroelectrochemical Studies on Mixed‐Valence States in a Cyanide‐Bridged Molecular Square, [Ru II 2 Fe II 2 ( μ ‐CN) 4 (bpy) 8 ](PF 6 ) 4 ⋅CHCl 3 ⋅H 2 O

A cyanide‐bridged molecular square of [Ru II 2 Fe II 2 ( μ ‐CN) 4 (bpy) 8 ](PF 6 ) 4 ⋅ CHCl 3 ⋅ H 2 O, abbreviated as [Ru II 2 Fe II 2 ](PF 6 ) 4 , has been synthesised and electrochemically generated mixed‐valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru II 2 Fe II 2 ] 4+ is nearly a square and is composed of alternate Ru II and Fe II ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru II 2 Fe II 2 ](PF 6 ) 4 in acetonitrile showed four quasireversible 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 2 Fe II 2 ] 4+ ⇄[Ru II 2 Fe II Fe III ] 5+ ⇄[Ru II 2 Fe III 2 ] 6+ ⇄[Ru II Ru III Fe III 2 ] 7+ ⇄[Ru III 2 Fe III 2 ] 8+ . Electrochemically generated [Ru II 2 Fe II Fe III ] 5+ and [Ru II 2 Fe III 2 ] 6+ showed new absorption bands at 2350 nm ( ε =5500  M −1 cm −1 ) and 1560 nm ( ε =10 500  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 delocalisation ( α 2 ) were estimated to be 1090 cm −1 and 0.065 for the [Ru II 2 Fe II Fe III 2 ] 5+ state and 1990 cm −1 and 0.065 for the [Ru II 2 Fe III 2 ] 6+ states.