Ligand-directed assembly of cyanide-bridged bimetallic Mn ^IIFe^III coordination polymers based on the pentacyanoferrite(III) building blocks

Rarely investigated pentacyanoferrate(III) building blocks, [Fe(CN) ₅(L)]^2- (L = 1-methylimdazole (1-CH₃im), imidazole (imH)), have been used to prepare cyanide-bridged bimetallic polymeric Mn(II)-Fe(III) complexes {[Mn(bpy)(H₂O)₂Fe(CN) ₅(1-CH₃im)]·H₂O}_n (1), {[Mn(bpy)Fe(CN)₅(imH)]·H₂O}_n (2) and {[Mn(CH₃OH)₂Fe(CN)₅(imH)]}_n (3) (bpy = 2,2′-bipyridine). Complexes 1 and 2 were obtained via the reactions of Mn(bpy)₂Cl₂·EtOH with [Fe(CN)₅(L)] ^2- (L = 1-CH₃im and imH, respectively), and complex 3via the reaction between MnCl₂·2H₂O and [Fe(CN) ₅(imH)]^2- in absolute methanol. Complex 1 is a one-dimensional alternate Mn(II)-Fe(III) chain, while complexes 2 and 3 are two-dimensional comprised of Fe₂Mn₂ squares. Complexes 2 and 3 show interesting intra- or interlayer π-π interactions between imidazole and pyridine rings of bpy. Partial loss of the bpy ligand and the π-π contacts has a direct effect on the molecular structures of complexes 1-3. Antiferromagnetic interaction between high-spin Mn(II), and low-spin Fe(III) has been observed in complexes 1-3, and the layered complexes 2 and 3 display long-range magnetic ordering at the critical temperature of 4.4 K (T_N) for 2 and 5.0 K (T_c) for 3. A best-fit to the magnetic susceptibility of the 1D complex 1 has given the magnetic coupling constant of J_MnFe = -6.16(9) cm^-1 based on an antiferromagnetic chain model of alternate S_Fe = 1/2 and S _Mn = 5/2 spins.