Mixed-metal single-molecule magnets: Syntheses, structure, and magnetic properties of [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl, CH 2Br, CHCl 2)

Abstract

Three mixed-metal single-molecule magnets containing [Mn 8Fe 4O 12] 16+ cores are synthesized and characterized. The reaction of FeCl 2·4H 2O with KMnO 4 and RCOOH (R = CH 2Cl, CH 2Br) in H 2O gives [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl ( 1), CH 2Br ( 2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl 2COOH in CH 2Cl 2 gives [Mn 8Fe 4O 12(O 2CCHCl 2) 16(H 2O) 4]·CH 2Cl 2·10H 2O ( 3·CH 2Cl 2·10H 2O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4Mn III, 4Fe III, and 4Mn IV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.