Novel bidentate 4-aroyl-5-pyrazolone ligands were synthesized and reacted with copper(II) and palladium(II) salts in 1:2 (metal:ligand) equimolar ratio leading to the formation of eight new coordination compounds. All synthesized compounds were characterized by FTIR, UV–Vis, ESI-Mass, 1H NMR, 13C-APT and also, in the case of the paramagnetic palladium(II) complexes, by ESR spectral studies. Additionally, elemental and thermogravimetric analyses (TG/DTG) were applied to all prepared complexes. These complexes are mononuclear and the copper(II) complexes have distorted square-planar geometry as determined by ESR. Spectral studies confirm the coordination of 4-aroyl-5-pyrazolone ligands through the carbonyl moieties to the metal. All the copper(II) complexes coordinated to the metal by enolization and the palladium(II) complexes showed ‘Type B’ coordination. The ligand which has 1-(4-methoxy)phenyl-substituted pyrazolone ring gave copper(II) complexes with a water molecule outside the coordination sphere. The proposed structures of the complexes agree well with the thermogravimetric decomposition results.