Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-Melm): [(MnO)-O-III(O2CCMe3)(6)(Im)(3)](Me3CCO)center dot 0.5Me(3)CCO(2

摘要

Two new mu(3)-oxo-centered trinuclear manganese complexes, one of them a homo-valence [(Mn3O)-O-III(O2CCMe3)(6)(Im)(3)](Me3CCO2)center dot 0.5Me(3)CCO(2)H (1) pivalate complex and the other a mixed-valence [(Mn2MnO)-Mn-III-O-II(O2CCMe3)(6)(1-MeIM)(3)] (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravinictric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are mu(3)-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-Melm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn3O(PiV)(6)(Im)(3)](+) and outersphere pivalate ions, whereas in compound 2 interactions of the C-H center dot center dot center dot pi type, formed by both the aromatic and methyl C-H groups of 1-Melm molecules, are present. Magnetic studies reveal that both compounds represent anti-ferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants. (c) 2006 Elsevier Ltd. All rights reserved.