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-bpb(2-)= R-substituted-1,2-bis(pyridine-2-carboxamido)benzenate) with trans-Mn(III) Schiff base complexes [Mn(5-X-saltn)]ClO4 (5-X-saltn(2-) = N,N'-propanolbis(5-X-substituted-salcylideneiminato) dianion) gave rise to cyanide-bridged neutral binuclear [MnFe] compounds [Mn(saltn)(MeOH)][Fe(bpb)(CN)(2)]center dot 3H(2)O ( 1), [Mn(saltn)(H2O)Fe(bpmb)(CN)(2)] center dot H2O (2), [Mn(saltn)(MeOH)Fe(bpClb)(CN)(2)]center dot 2H(2)O ( 3), and ionic [Mn2Fe](+)-[Fe](-) complexes [Mn-2(5-Br-saltn)(2)(H2O)(EtOH)Fe(bpb)(CN)(2)][Fe(bpb)(CN)(2)]center dot 6H(2)O ( 4) and [Mn-2(5-Cl-saltn)(2)(CH3OH)(EtOH)Fe(bpb)(CN)(2)][Fe(bpb)(CN)(2)]center dot 5H(2)O center dot MeCN (5). Four binuclear units of complexes 1-3 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 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.