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

A series of five coordination compds., namely, [Co3(stp)2(bipy)(H2O)4]·2H2On, (1), [Co3(stp)2(bipy)5(H2O)6]·4H2On, (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 synthesized 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 topol. diverse with the connectivities of the materials dependent on the ratios of starting materials employed. Single-crystal x-ray diffraction studies show that compd. 1 is a three-dimensional coordination polymer, compd. 2 consists of infinite one-dimensional zigzag chains, compd. 3 is a discrete trinuclear complex, compd. 4 is a discrete mononuclear complex and compd. 5 is an ionic solid consisting of both cobalt contg. 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 sepns. Modeling required the introduction of zero field splitting parameters due to orbital angular momentum contributions in these cases. [on SciFinder(R)]