Ligand-directed assembly of cyanide-bridged bimetallic (MnFeIII)-Fe-II coordination polymers based on the pentacyanoferrite(III) building blocks

摘要

Rarely investigated pentacyanoferrate(III) building blocks, [Fe(CN)(5)(L)](2-) (L = 1-methylimdazole (1-CH(3)im), imidazole (imH)), have been used to prepare cyanide-bridged bimetallic polymeric Mn(II)-Fe(III) complexes {[Mn(bpy)(H2O)(2)Fe(CN)(5)(1-CH(3)im)]center dot H2O}(n) (1), {[Mn(bpy)Fe(CN)(5)(imH)]center dot H2O}(n) (2) and {[Mn(CH3OH)(2)Fe(CN)(5)(imH)]}(n) (3) (bpy 2,2'-bipyridine). Complexes 1 and 2 were obtained via the reactions of Mn(bpy)(2)Cl-2 center dot EtOH with [Fe(CN)(5)(L)](2-) (L = 1-CH(3)im and imH, respectively), and complex 3 via the reaction between MnCl2 center dot 2H(2)O 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 pi-pi interactions between imidazole and pyridine rings of bpy. Partial loss of the bpy ligand and the pi-pi 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.