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

Four heterobimetallic trinuclear Fe-Cu-Fe complexes [Cu(cyclam)][Fe(bpb)(CN)]·4HO ( 1), [Cu(cyclam)][Fe(bpClb)(CN)]·4HO ( 2), [Cu(cyclam)][Fe(bpmb)(CN)]·4HO ( 3) and [Cu(cyclam)][Fe(bpdmb)- (CN)]·HO ( 4) (cyclam = 1,4,8,11-tetraazacyclotetradecane, bpb = 1,2-bis(pyridine-2-carboxamido), bpClb = 1,2-bis(pyridine-2-carboxamido)-4-chloro-benzenate, bpmb = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate, bpdmb = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate) have been synthesized based on cyanide-containing building blocks [Fe(L)CN] (L = bpb, bpClb, bpmb and bpdmb) and [Cu(cyclam)]. 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 for 1, −0.70 cm for 2, −0.93 cm for 3 and −0.85 cm for 4 based on the Hamiltonian Ĥ = −2 JŜ( Ŝ + Ŝ). 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. [ABSTRACT FROM AUTHOR]