Copper(II) and cobalt(II) hydroxypyridinecarboxylates:: Synthesis, crystal structures, spectral and magnetic properties

Synthesis and characterization of six copper(II) and cobalt(II) octahedral complexes [M(6-OHpic)(2)(H2O)(2)] (6-OHpic is 6-hydroxypicolinato), [M(2-OHnic)(2)(H2O)(2)] (2-OHnic is 2-hydroxynicotinato), [Cu(6-OHnic)(2)(H2O)(2)] (6-OHnic is 6-hydroxynicotinato) as well as [Co(H2O)(6)](6-OHnic)(2) are reported. Their characterization was carried out using elemental analysis, infrared, and magnetic measurements. Based on IR spectra, N,O-coordination of 6-OHpic (via the oxygen atom of the carboxyl group and the nitrogen atom of the pyridine ring), O,O-asymmetrically chelating coordination of the carboxyl groups as well as ionic coordination of 6-OHnic and chelating O,O-coordination (through the oxygen atom of the carboxyl group and the oxygen atom of the amide group) of keto(amide) tautomer of 2-OHnic were supposed. Moreover, crystal structures of 2-OHnicH and the complex [Co(2-OHnic)(2)(H2O)(2)]) were determined by X-ray single crystal structure analysis. The system of hydrogen bonds predominantly stabilizes the keto(amide) tautomer of both 2-hydroxynicotinic acid and 2-OHnic anion in the cobalt(II) complex. Intermolecular hydrogen bonds (between the oxygen atom of the amide group and the hydrogen atom of the NH group) interconnect two neighbouring molecules of 2-OHnicH forming dimers. Cobalt(II) in complex [Co(2-OHnic)(2)(H2O)(2)] has nearly a regular compressed tetragonal bipyramidal arrangement. (C) 2008 Institute of Chemistry, Slovak Academy of Sciences.