Cu2+ and VO2+ doped single crystals of [Co(sac)(2)(H2O)(4)].2H(2)O (Cosacaqua) complex were investigated using EPR technique at ambient temperature. Detailed investigation of the EPR spectra indicated that the Cu2+ and VO2+ substitute the Co2+. Two sites were observed for Cu2+ and VO2+. But each site of V4+ corresponds two different orientations of VO2+. The principal values of the g and the hyperfine tensors were obtained. The spectra indicate that the ground state for Cu2+ is mainly 3d(x2-y2). The covalent bonding parameters for Cu2+ and VO2+ and Fermi contact terms were obtained. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.