Synthesis, Structural Characterizations and Magnetic Properties of a Series of Mono‐, Di‐ and Polynuclear Manganese Pyridinecarboxylate Compounds

Seven new manganese(II, III, IV) pyridinecarboxylate compounds (Et4N)[MnCl2(pic)2] (1, Hpic = picolinic acid) [MnCl(pic)2(H2O)]·H2O (2), [MnCl(pic)(H2O)2]n (3), [Mn(pic)2]n (4), [MnCl(pic)]n (5), [MnCl2(4‐C5H4NHCOO)]n (6) and [Mn2O2(pic)4] (7) were synthesized and structurally characterized. The picolinate ligand coordinates to the Mn ion forming a chelating five‐membered ring which constructs diverse architectures by various bridging modes, such as μ‐Cl, μ1,1‐ and μ1,3‐carboxylate bridges (syn‐syn and syn‐anti modes). The interaction between the pyridyl rings is discussed, displaying a face‐to‐face π‐π stacking for complex 6 and a T‐shaped C−H···π attraction for complex 4. Complex 3 has an infinite zigzag chain structure in which two neighboring Mn ions are linked by a carboxylate bridge in a syn‐anti mode. In complex 4, the Mn(pic)2 fragments are joined to each other by double μ1,1‐carboxylate bridges, forming a 2D layer structure. Complex 5 contains Mn4O4 square subunits which are connected by double μ‐Cl bridges to form a grid‐like 2D structure. The isonicotinate complex 6 has a zigzag chain structure containing mixed double μ‐Cl and μ1,3‐carboxylate bridges in a syn‐syn mode. Protonation at the pyridyl‐N position was found and identified by the IR and magnetic properties of 6. The participation of an oxidizing agent like MnO4− leads to complexes containing higher valent manganese (1, 2 and 7). The IR spectra of these complexes are discussed and found to be consistent with the structural features. The magnetic properties of complexes 4, 5 and 6 have been investigated. Antiferromagnetic coupling interactions were observed and satisfactory fitting results were obtained with J values ranging from −0.63 cm−1 to −2.35 cm−1. The magnetic parameters of these complexes, together with the parameters of other Mn complexes with comparable structures, are compared and discussed based on the bridging modes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)