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
* Corresponding author: E-mail: zpopovic@chem.pmf.hr
Fax: +385-1-4606341, Tel. +385-1-4606354
Abstract
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