Syntheses, crystal structures, and magnetic characterization of five new dimeric manganese(III) tetradentate Schiff base complexes exhibiting single-molecule-magnet behavior

Tetradentate Schiff base ligands H2L (H(2)saltmen, H(2)salen, H-2-5-Brsalen, and H-2-3,5-Brsalen), derived from the condensation of the corresponding salicylaldehyde or its derivatives with 1,1,2,2-tetramethylethyldiamine or 1, 2-diaminoethane, reacted with Mn-III acetate or perchlorate salts and sodium azide or sodium cyanate to produce five Mn-III dimer complexes, [Mn(saltmen)(O2CCH3)](2)(.)2CH(3)CO(2)H (1), [Mn(saltmen)(N-3)](2) (2), [Mn(salen)(NCO)](2) (3), [Mn(3,5-Brsalen)(3,5-Brsalicylaidehyde)](2) (4), and [Mn(5-Brsalen)(CH3OH)](2)(CIO4)(2) (5). These new complexes have been characterized by IR, elemental analyses, crystal structural analyses, and magnetic studies. Within these Mn-III dimeric complexes, two Mn-III ions are connected by phenolate oxygen atoms with acetate, azide, cyanate, a 3,5Brsalicylaclehyde anion, and a neutral methanol molecule as the axial ligands for complexes 1-5, respectively. Complexes 1-4 exhibit intradimer ferromagnetic exchange and display frequency dependence of ac magnetic susceptibility, possibly showing single-molecule-magnet (SMM) behavior. In contrast, complex 5 shows an intradimer antiferromagnetic coupling probably originating from the relatively shorter Mn-O* distance, compared to those of complexes 1-4.