Coordination compounds of tetrazolate-5-carboxylate with cobalt(II): Synthesis, structure and magnetic properties

Four coordination compounds of tetrazolate-5-carboxylate (tzc) with cobalt(II), [Co₂(tzc)₂(H₂O)₆] ·2H₂O (1), [Co₂(tzc)₂(phen) ₂(H₂O)₂]·2H₂O (2), [Co ₂(tzc)₂(2,2′-bpy)₂(H₂O) ₂]·H₂O (3), and [Co(tzc)(4,4′-bpy)] (4), where phen = 1,10-phenanthroline, 2,2′-bpy = 2,2′-bipyridyl, and 4,4′-bpy = 4,4′-bipyridyl, have been synthesized by the hydrothermal methods involving the in situ generation of the ligand from sodium ethyl tetrazolate-5-carboxylate. Compounds 1, 2 and 3 all contain dinuclear molecules in which metal ions are linked by the double N-N bridges from two tzc ligands in the μ₂-N₁,O₁:N₂ mode, and the dinuclear molecules are associated into 3D architecture through extensive hydrogen bonding and π-π stacking interactions in various fashions. Compound 4 exhibits a two-dimensional layer structure in which Co(tzc) chains with μ₃-N₁,O₁:O₁:N₂ tzc are cross-linked by 4,4′-bpy. Magnetic investigations on 1-3 revealed intramolecular ferromagnetic coupling through the double N-N bridges with intermolecular ferromagnetic or antiferromagnetic interactions. The interaction through the mixed N-N and μ₂-O_carboxylate bridges in 4 is antiferromagnetic.