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 (H2saltmen, H2salen, H2-5-Brsalen, and H2-3,5-Brsalen), derived from the
condensation of the corresponding salicylaldehyde or its derivatives with 1,1,2,2-tetramethylethyldiamine or 1,
2-diaminoethane, reacted with MnIII acetate or perchlorate salts and sodium azide or sodium cyanate to produce
five MnIII dimer complexes, [Mn(saltmen)(O2CCH3)]2·2CH3CO2H (1), [Mn(saltmen)(N3)]2 (2), [Mn(salen)(NCO)]2 (3),
[Mn(3,5-Brsalen)(3,5-Brsalicylaldehyde)]2 (4), and [Mn(5-Brsalen)(CH3OH)]2(ClO4)2 (5). These new complexes have
been characterized by IR, elemental analyses, crystal structural analyses, and magnetic studies. Within these MnIII
dimeric complexes, two MnIII ions are connected by phenolate oxygen atoms with acetate, azide, cyanate, a 3,5-Brsalicyladehyde 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.