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

A series of five coordination compounds, namely, {[Co3(stp)2(bipy)(H2O)4]&#183;2H2O}n, (1), {[Co3(stp)2(bipy)5(H2O)6]&#183;4H2O}n, (2), [Co3(stp)2(bipy)4(H2O)10]&#183;8H2O, (3), [Co(Hstp)2(Hbipy)2], (4) and {[Co(stp)2(H2O)2][Co(bipy)2(H2O)4]}&#183;2Hbipy&#183;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.