Supramolecular metallomacrocycles based on trans-dicyanoferrite(III) building blocks: synthesis, crystal structure and magnetic properties†
Abstract
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 (1), [Mn(saltn)(H2O)Fe(bpmb)(CN)2]·H2O (2), [Mn(saltn)(MeOH)Fe(bpClb)(CN)2]·2H2O (3), and ionic [Mn2Fe]+-[Fe]− complexes [Mn2(5-Br-saltn)2(H2O)(EtOH)Fe(bpb)(CN)2][Fe(bpb)(CN)2]·6H2O (4) and [Mn2(5-Cl-saltn)2(CH3OH)(EtOH)Fe(bpb)(CN)2][Fe(bpb)(CN)2]·5H2O·MeCN (5). Four binuclear units of complexes 1–3 assemble in a head-to-tail way viahydrogen bonding giving rise to a metallo-supramolecular [MnFe]4 square, while two [Mn2Fe]+-[Fe]− units of complexes 4–5 form a metallo-supramolecular macrocyclic structure. Magnetic studies reveal that complexes 1–3 and 5 exhibit intermetallic ferromagnetic coupling, while complex 4 displays antiferromagnetic interaction between low-spin Fe(III) and high-spin Mn(III) through the cyanide bridges. Complexes 1, 4 and 5 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 4 shows an exchange-biased single-molecule magnet (SMM) behavior below 0.5 K.