Coordination chemistry of tetrazolate-5-carboxylate with manganese(II): synthesis, structure and magnetism

Six Mn(II) coordination compounds with tetrazolate-5-carboxylate (tzc), have been synthesized and characterized. They are of the formula [Mn-2(tzc)(2)(H2O)(2)]center dot 4H(2)O (1), Mn(tzc)(H2O)(2) (2), [Mn-2(tzc)(2)(phen)(2)(H2O)(2)] (3),[Mn(tzc)(2,2'-bpy)(H2O)(2)] (4),[Mn(tzc)(4,4'-bpy)] (5) and [Mn-2(tzc)(2)(H2O)(2)]center dot(bpp) (6), where phen =1,10-phenanthroline,2,2'-bpy = 2,2'-bipyridyl, 4,4'-bpy = 4,4'-bipyridyl, and bpp = 1,3-di(4-pyridyl) propane. Versatile coordination modes of the tzc ligand have been recognized in these compounds. In the absence of auxiliary ligands, a dinuclear compound ( 1) with the Mn-2(N-N)(2) moiety and a 1D coordination polymer (2) consisting of two types of disordered Mn( tzc) chains have been obtained at different temperatures. The incorporation of chelating auxiliary ligands ( 2,2'-bpy and phen) leads to a mononuclear ( 4) and a dinuclear ( 3) compounds, the structure of the latter resembling that of 1. The use of the ditopic auxiliary ligand 4,4'-bpy gives a 2D coordination polymer ( 5) in which disordered Mn(tzc) chains are cross-linked by 4,4'-bpy. However, the potentially ditopic ligand bpp is not involved in coordination but serves as hydrogen-bonded bridge between the Mn( tzc) chains to give compound 6. Magnetic investigations suggest that the double N-N bridges in the dinuclear compounds (1 and 3) mediate weak ferromagnetic coupling. However, in compounds 2, 5 and 6, which consist of 1D disordered Mn(tzc) chains with different bridging moieties, the intra-chain interactions are dominated by antiferromagnetic coupling.