Supramolecular metallomacrocycles based on trans-dicyanoferrite(III) building blocks: synthesis, crystal structure and magnetic properties.

The reaction of trans-[Fe(R-bpb)(CN)2]- (R-bpb2-=R-substituted-1,2-bis(pyridine-2-carboxamido)benzenate) with trans-Mn(III) Schiff base complexes [Mn(5-X-saltn)]ClO4 (5-X-saltn2-=N,N'-propanolbis(5-X-substituted-salcylideneiminato) dianion) gave rise to cyanide-bridged neutral binuclear [MnFe] compounds [Mn(saltn)(MeOH)][Fe(bpb)(CN)2].3H2O (), [Mn(saltn)(H2O)Fe(bpmb)(CN)2].H2O (), [Mn(saltn)(MeOH)Fe(bpClb)(CN)2].2H2O (), and ionic [Mn2Fe]+-[Fe]- complexes [Mn2(5-Br-saltn)2(H2O)(EtOH)Fe(bpb)(CN)2][Fe(bpb)(CN)2].6H2O () and [Mn2(5-Cl-saltn)2(CH3OH)(EtOH)Fe(bpb)(CN)2][Fe(bpb)(CN)2].5H2O.MeCN (). Four binuclear units of complexes assemble in a head-to-tail way via hydrogen bonding giving rise to a metallo-supramolecular [MnFe]4 square, while two [Mn2Fe]+-[Fe]- units of complexes form a metallo-supramolecular macrocyclic structure. Magnetic studies reveal that complexes and exhibit intermetallic ferromagnetic coupling, while complex displays antiferromagnetic interaction between low-spin Fe(III) and high-spin Mn(III) through the cyanide bridges. Complexes , and display frequency dependent of current-alternating (ac) magnetic susceptibility, typical of the presence of slow magnetization relaxation. Because of the existence of intermolecular magnetic interaction, complex shows an exchange-biased single-molecule magnet (SMM) behavior below 0.5 K.