Three new copper(II) complexes of 5,5-diethlybarbiturate (barb), [Cu(barb)(2)(dmen)] center dot 0.5H(2)O (dmen = N, N-dimethylethylenediamine) 1, [Cu(barb) 2(bapa)] (bapa = bis(3-aminopropyl) amine) 2, and [Cu(barb)(apen)](barb) center dot 2H(2)O (apen = N, N'-bis(3-aminopropyl) ethylenediamine) 3, have been synthesized and characterized by chemical, spectroscopic and thermal methods. Single crystal X-ray diffraction studies revealed that all complexes are mononuclear. The copper(II) ion exhibits a square-pyramidal coordination geometry in 1 and 3, but a trigonal-bipyramidal geometry in 2. The barb ligand shows different coordination modes. 1 presents the unequal coordination of the barb ligands: one is monodentate (N) and the other one is bidentate (N, O). In 2, both barb ligands are N-coordinated, whereas in 3, one barb ligand is N-coordinated, while the second barb ligand behaves as a counter-ion. The dmen, bapa and apen ligands act as bi-, tri- and tetradentate ligands, respectively. All complexes display a hydrogen-bonded network structure. The IR spectroscopic analysis shows that the nu(CO) stretching frequencies do not correlate predictably with the coordination mode of the barb ligand in 1. Thermal analysis data for 1-3 are in agreement with the crystal structures. (C) 2009 Elsevier B. V. All rights reserved.