The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af)(2)(H2O)(2)](NO3)(2) center dot nH(2)O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af)(2)(NO3)(2)] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af)(2)(NO3)(2)] (1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N,O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) (2) and cobalt(II) (3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8-300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin-orbit-coupling and also suggests a weak ferromagnetic interaction. (C) 2008 Elsevier B. V. All rights reserved.