Single crystals and powder electron paramagnetic resonance (EPR) studies of Cu2+-doped disodium malonate trihydrate [C3H2O4Na2 center dot 3H(2)O] have been carried out at room temperature. The angular variation of the disodium malonate trihydrate single crystal have shown that two different Cu2+ complexes are located in different chemical environments, and each environment contains one magnetically inequivalent Cu2+ sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal values of the g and the hyperfine tensors were determined and were found to be in agreement with the literature values. Crystal field around the Cu2+ ion is nearly rhombic. The optical absorption studies show two bands at 603 nm (16584 cm(-1)) and 890 nm (11236 cm(-1)) which confirm the rhombic symmetry. The crystals field parameters and than the wave function are determined. (c) 2008 Elsevier B.V. All rights reserved.