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

Boris-Marko Kukovec,a Zora Popovića,* and Gordana Pavlovićb

a Laboratory of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia
b Laboratory of General Chemistry, Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz baruna Filipovića 28a, HR-10000 Zagreb, Croatia
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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 π···π stacking interactions which form a complex three-dimensional supramolecular architectures.

Keywords: Copper(II) complexes; 3- and 6-hydroxypicolinic acids; IR spectroscopy; Thermal analysis (TGA/DTA);
Crystal structure; π···π stacking interactions