Copper(II) Complexes with 3- and 6-hydroxypicolinic Acid. Preparation, Structural, Spectroscopic and Thermal Study

Copper(II) complexes of 3-hydroxypicolinic acid (3-OHpicH), namely {Cu(3-OHpic)2}(1), {Cu(3-OHpic)2(4-pic)}(2) and of 6-hydroxypicolinic acid (6-OHpicH), namely {Cu(6-OHpic)2(H2O)2}(3) and {Cu(6-OHpic)2(4-pic)2}(4) were prepared and characterized by IR spectroscopy and thermal analysis (TGA/DTA). Molecular and crystal structures of 2 and 4 were determined by X-ray crystal structure analysis. Complexes 1 and 3 were prepared by reaction of copper(II) sulfate pentahydrate with 3-hydroxypicolinic and 6-hydroxypicolinic acid, respectively, in aqueous solution, while 2 and 4 were prepared by recrystallization of 1 and 3 from 4-picoline solution. Structure analysis revealed square-pyramidal copper(II) coordination in 2. Copper(II) ion is coordinated by two 3-OHpic ligands in the basal plane of square pyramid and by 4-picoline molecule in the axial position in the structure of 2. In the structure of 4, copper(II) is coordinated by two 6-OHpic ligands in the equatorial plane and by two 4-picoline molecules in the axial positions, leading to a distorted 4 + 2 octahedral coordination. The crystal packings of both 2 and 4 are dominated by intermolecular C–H•••O hydrogen contacts and p•••p stacking interactions which form a complex three-dimensional supramolecular architectures.