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]·4H ₂O (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 [Mn₂(tzc)₂(H ₂O)₂]·(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 Mn₂(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.