Syntheses and crystal structures of four cyanide-bridged trinuclear iron(III)–copper(II)–iron(III) complexes exhibiting abnormal antiferromagnetic coupling

Abstract

Four heterobimetallic trinuclear FeШ–CuII–FeШ complexes [Cu(cyclam)][Fe(bpb)(CN)2]2·4H2O (1), [Cu(cyclam)][Fe(bpClb)(CN)2]2·4H2O (2), [Cu(cyclam)][Fe(bpmb)(CN)2]2·4H2O (3) and [Cu(cyclam)][Fe(bpdmb)- (CN)2]2·H2O (4) (cyclam = 1,4,8,11-tetraazacyclotetradecane, bpb2– = 1,2-bis(pyridine-2-carboxamido), bpClb2− = 1,2-bis(pyridine-2-carboxamido)-4-chloro-benzenate, bpmb2− = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate, bpdmb2– = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate) have been synthesized based on cyanide-containing building blocks [Fe(L)CN2]− (L = bpb2−, bpClb2−, bpmb2− and bpdmb2−) and [Cu(cyclam)]2+. Their structures and magnetic properties were investigated. The single-crystal X-ray diffraction analyses reveal that they are all neutral trinuclear sandwich-like structures. Magnetic investigations show that they are all abnormal antiferromagnetic, with J = −0.95 cm−1 for 1, −0.70 cm−1 for 2, −0.93 cm−1 for 3 and −0.85 cm−1 for 4 based on the Hamiltonian Ĥ = −2 JŜ Cu(Ŝ Fe(1) + Ŝ Fe(2)). The abnormal antiferromagnetic coupling between Fe(III) and Cu(II) in the four complexes can be attributed to the small Cu–N≡C bond angles.