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

Abstract

Six Mn(II) coordination compounds with tetrazolate-5-carboxylate (tzc), have been synthesized and characterized. They are of the formula [Mn₂(tzc)₂(H₂O)₂]·4H₂O (1), Mn(tzc)(H₂O)₂ (2), [Mn₂(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(H₂O)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.