Cyanide-Bridged Molecular Squares with Ferromagnetically Coupled dπ, dσ, and pπ Spin System

Abstract

Cyanide-bridged molecular squares of [FeII2CuII2(μ-CN)4(dmbpy)4(impy)2](ClO4)4·4CH3OH·C6H6 (1) and of [FeIII2CuII2(μ-CN)4(dmbpy)4(impy)2](ClO4)6·4CH3OH·4H2O (2) (dmbpy = 4,4‘-dimethyl-2,2‘-bipyridine; impy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy) were prepared. In the squares of 1 and 2, the Fe(II/III) (low spin) and Cu(II) ions are alternately bridged by the cyanide groups, in which the cyanide carbon atoms coordinated to the Fe(II) ions and Cu(II) ions are coordinated by imino nitroxide. Magnetic susceptibility measurements for 1 and 2 revealed that the Cu(II) ion and imino nitroxide are ferromagnetically coupled with a fairly strong coupling constant (JCu-radical > 300 K) and act as triplet species. In 1 the Cu(II)−radical moieties are magnetically separated by the Fe(II) ions. In the square of 2, dπ (Fe(III)), dσ (Cu(II)), and pπ (imino nitroxide) spins are alternately assembled, and this situation allowed the square to have an S = 3 spin ground state. The exchange coupling constant of Fe(III) and the Cu(II)−radical moiety in 2 was estimated to be J = 4.9 cm-1 (H = −2J∑SFe·SCu-radical)