Single crystals of transition metal ions Cu2+ doped disodium maleate monohydrate, [C4H2O4Na2 center dot H2O], have been grown by solvent evaporation of the saturated aqueous solution at room temperature and investigated by single crystal EPR spectral studies. Angular variation of copper hyper. ne lines in the three orthogonal planes shows the presence of two magnetically inequivalent substitutional Cu2+ sites in the lattice. The principal values of the g- and A-tensors indicate nearly axial symmetry around the Cu2+ ion. Direction cosines of the principal values of the g- and A-tensors have been determined. Bonding parameters were evaluated and the ground state wave function of the Cu2+ ion was constructed. (C) 2009 Elsevier B.V. All rights reserved.