Preparation, structural and thermal characterization of cobalt(II) and copper(II) complexes with 3-hydroxypicolinamide

Abstract

Cobalt(II) and copper(II) complexes of 3-hydroxypicolinamide (3-OHpia), namely [Co(3-OHpia)2(H2O)2](NO3)2 (1), [Co(3-Opia)2(H2O)2] (2) and [Cu(3-OHpia)2(NO3)2] (3), were prepared and characterized by IR spectroscopy and TG/DTA methods. The molecular and crystal structures of 1 and 3 were determined by X-ray crystal structure analysis. Complexes 1 and 3 were obtained by reaction of 3-hydroxypicolinamide with cobalt(II) nitrate or copper(II) nitrate, respectively, in a mixture of ethanol and water. Complex 2 was prepared by reaction of cobalt(II) acetate and 3-OHpia in aqueous solution. X-ray structural analysis revealed octahedral coordination polyhedra in both 1 and 3 and the same N,O-chelated coordination mode of 3-OHpia. The coordination sphere of the cobalt(II) center in 1 is completed by two coordinated water ligands and that of the copper(II) center in 3 by two coordinated nitrate anions. There are also two uncoordinated nitrate ions in 1 which compensate the positive charge of cobalt(II). The crystal structures of 1 and 3 are dominated by intermolecular O–H···O and N–H···O hydrogen bonds. The thermogravimetric study indicated the loss of two coordinated water molecules in 1 and 2 and of one 3-OHpia ligand together with N2 molecule in 3 at lower temperatures (up to 300 °C).