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 (TGA/DSC) 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.