Competing Exchange Interactions and Ground-State Variability: Linear Homo- and Heterotrinuclear Manganese(III, IV) Complexes with Tris(dimethylglyoximato)metalate(II) Tetraanions as Bridging Ligands

Two series of linear homo- and heterotrinuclear complexes, MnIIIMIIMnIII and MnIVMIIMnIV, where MII represents MnII (1 and 5), NiII (2 and 6), CuII (3 and 7), or ZnII (4 and 8), containing three dimethylglyoximato dianions (dmg2-) as bridging ligands and 1,4,7-trimethyl-1,4,7-triazacyclononane (L) as the capping ligand for the terminal MnIII or MnIV ions, have been synthesized. Compounds 1−8 have been characterized on the basis of elemental analyses, IR, UV−vis, and EPR spectroscopy, and variable-temperature (2−295 K) magnetic susceptibility measurements. The trinuclear complexes are quasi-isostructural with the terminal manganese ions in a distorted octahedral environment, MnIII/IVN3O3, and the divalent metal ions M are six-coordinate with the MIIN6 chromophore. The molecular structures of the compounds [LMnIII{(μ-dmg)3MnII}MnIIIL](ClO4)2 (1) and [LMnIII{(μ-dmg)3CuII}MnIIIL](ClO4)2 (3) have been established by X-ray diffraction. 1 crystallizes in the monoclinic system, space group C2/c, with cell constan...