Discrete and polymeric complexes formed from cobalt(ii), 4,4′-bipyridine and 2-sulfoterephthalate: synthetic, crystallographic and magnetic studies

Abstract

A series of five coordination compounds, namely, {[Co₃(stp)₂(bipy)(H₂O)₄]·2H₂O}_n, (1), {[Co₃(stp)₂(bipy)₅(H₂O)₆]·4H₂O}_n, (2), [Co₃₍stp)₂(bipy)₄(H₂O)₁₀]·8H₂O, (3), [Co(Hstp)₂(Hbipy)₂], (4) and {[Co(stp)₂(H₂O)₂][Co(bipy)₂(H₂O)₄]}·2Hbipy·2H₂O, (5) have been synthesised hydrothermally, through the reaction of different molar ratios of 2-sulfoterephthalic acid monosodium salt, Na(H₂stp), cobalt(II) nitrate hexahydrate and the N-donor ancillary co-ligand 4,4′-bipyridine (bipy). Due to the combination of the multiple potential coordination modes of the stp ligand and the bipy co-ligand, the products are structurally and topologically diverse with the connectivities of the materials dependent on the ratios of starting materials employed. Single-crystal X-ray diffraction studies show that compound 1 is a three-dimensional coordination polymer, compound 2 consists of infinite one-dimensional zig-zag chains, compound 3 is a discrete trinuclear complex, compound 4 is a discrete mononuclear complex and compound 5 is an ionic solid consisting of both cobalt containing cations and anions. Magnetic studies show that the Co(II) ions in 1 are strongly coupled, while 2, 3 and 5 show insignificant coupling due to larger metal–metal separations. Modelling required the introduction of zero field splitting parameters due to orbital angular momentum contributions in these cases.