New copper(II) and palladium(II) complexes were synthesized by the interaction of metal acetates and azo-, bisazo-5-pyrazolones in a methanolic medium. The mononuclear copper(II) and palladium(II) complexes were obtained from the ligands, HAP/HL1a-b and HAP/HL2 (Azo-5-Pyrazolone Ligand), and the binuclear copper(II) complexes were obtained from the ligands, HBAP/HL2a and HBAP/HL1c (BisAzo-5-Pyrazolone Ligand). The resulting complexes were characterized on the basis of spectroscopic techniques such as infrared, mass spectra, nuclear magnetic resonance and UV-visible absorption spectra as well as thermal analyses. The spectral data show that the ligands coordinated via the carbonyl oxygen of 5-pyrazolone and via the azo group of the nitrogen atoms of the azo-, bisazo-5-pyrazolones, except for the complex [Pd(HL1a)(2)] which coordinated from the carbonyl oxygen of 5-pyrazolone and the hydroxyl oxygen of the azo-substituted aromatic ring. (C) 2013 Elsevier B. V. All rights reserved.