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Synthesis and structure of cobalt(II) complexes with hydroxyl derivatives of pyridinecarboxylic acids. Conformation analysis of ligands in the solid state.

Cobalt(II) complexes of 6-hydroxypicolinic acid (6-OHpicH), namely [Co(6-OHpic)2(H2O)2] (1) and [Co(6-OHpic)2(4-pic)2]∙ 4-pic (2), and of 2-hydroxynicotinic acid (2-OHnicH), [Co(2-OHnic)2(H2O)2] (3) were prepared. The crystal structures of free 6-hydroxypicolinic acid monohydrate [6-OHpicH]• H2O (4), and the novel polymorph of 2-hydroxynicotinic acid [2-OHnicH] (5) and complex 2 were determined by X-ray crystal structure analysis. All compounds were characterized by IR-spectroscopy and thermal methods and data are in agreement with the structure analysis. It was established that 4 and 5 exist in solid state in keto-tautomeric form. For 2, structure analysis revealed N, O-chelating mode of 6-hydroxypicolinic acid.

Cobalt(II) complexes; 6-hydroxypicolinic acid; 2-hydroxynicotinic acid; Polymorphism; Crystal structures; IR-spectra; TGA/DSC measurements

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