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)](PF6) with [ Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic te tranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2) O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH( 3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ ( low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the ca rbon atoms of which coordinate to the iron ions. Variable-temperature magne tic susceptibility studies of complexes revealed that the Cu2+ ions in 1 ar e magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ion s were ferromagnetically coupled through the cyanide bridges with a J(1) va lue of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ 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 Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been rec orded and discussed. Crystal data for 1: triclinic space group P (1) over b ar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees , Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.4 72(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.5 8(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.