Cyanide-Bridged Iron−Copper Molecular Squares with Doublet and Quintet Spin Ground States

Reactions of [Fe II (CN) 2 (bpy) 2 ] and [Fe III (CN) 2 (bpy) 2 ](PF 6 ) with [Cu II (bpy)(CH 3 OH) 2 ](PF 6 ) 2 in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [Fe II 2 Cu II 2 (μ-CN) 4 (bpy) 6 ](PF 6 ) 4 ·2H 2 O·4CHCl 3 ( 1 ) and [Fe III 2 Cu II 2 (μ-CN) 4 (bpy) 6 ](PF 6 ) 6 ·4CH 3 CN·2CHCl 3 ( 2 ), respectively. In the squares of 1 and 2, the Fe 2+/3+ (low-spin) and Cu 2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu 2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe 3+ and Cu 2+ ions were ferromagnetically coupled through the cyanide bridges with a J 1 value of +6.3(1) cm - 1 and the weaker antiferromagnetic interactions between the orthogonal Fe 3+ ···Fe 3+ and Cu 2+ ···Cu 2+ pairs are operative ( J 2 = −3.1(1) cm - 1 ). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe 3+ (dπ) and Cu 2+ (dσ) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P 1̄, a = 14.491(4) Å, b = 15.312(4) Å, c = 12.959(3) Å, α = 91.38(2)°, β = 109.56(2)°, γ = 65.41(2)°, Z = 1. Crystal data for 2: triclinic space group P 1̄, a = 14.472(9) Å, b = 15.310(6) Å, c = 12.523(5) Å, α = 102.58(3)°, β = 107.19(4)°, γ = 75.08(4)°, Z = 1.