MOLECULAR-STRUCTURE AND SPECTRAL PROPERTIES OF MONONUCLEAR AND DINUCLEAR COMPLEXES FORMED BY MANGANESE(II), 2,6-DIMETHOXYBENZOATE AND 2,2'-BIPYRIDINE OR 2-METHYLPYRAZINE

The adducts formed by reaction of [Mn(dmb)(2)(H2O)(3)](n) . nH(2)O, dmb = 2,6-dimethoxybenzoato(1-), with 2,2'-bipyridine (bpy) or 2-methylpyrazine (2-Mepz) were isolated in the solid state and characterized by single crystal X-ray diffraction, IR and EPR spectroscopy, and thermogravimetry. The adduct [Mn-2(dmb)(4)(bpy)(2)(H2O)(2)]. bpy crystallizes in the monoclinic space group P2(1)/n, with a = 15.983(4), b = 11.048(4), c = 17.682(4) Angstrom, beta = 97.66(3)degrees, V = 3094.4(16) Angstrom(3), A = 2 and D-calc = 1.415 g cm(-3). The complex exhibits a dinuclear structure where two manganese(II) atoms share two carboxylate groups adopting a rather uncommon single-atom bridging mode. The coordination at each metal nucleus is completed by a further carboxylate group, acting as a monodentate donor, a water molecule and a chelating bidentate bipyridine molecule. The crystals of the adduct [Mn(dmb)(2)(2-Mepz)(2)(H2O)(2)] are monoclinic, space group P2(1)/n, with a = 8.024(3), b = 10.314(3), c = 18.289(4) Angstrom, beta = 94.72(3)degrees, V = 1508.5(8) Angstrom(3), Z = 2 and D-calc = 1.412 g cm(-3). The compound is mononuclear and consists of hexacoordinate ions bound to trans-pairs of monodentate carboxylates, water molecules and nitrogenous base molecules. The bpy adduct exhibits EPR spectra distinctive of magnetically coupled dimanganese(II) units.