Electron paramagnetic resonance (EPR) studies of copper ions, Cu(II), as paramagnetic impurity in tetraaqua-di(nicotinamide) Zn(II)saccharinates single crystals [Zn(nic)(2)(H2O)(4)](sac)(2), have been investigated at ambient temperature. The detailed EPR analysis shows the only one site and the copper ion entered the lattice substitutionally in place of Zn(II). The spin-Hamiltonian parameters were obtained from the single crystal EPR analysis. By using the EPR data, molecular bonding coefficient and the Fermi contact interaction terms have been evaluated. Superhyperfine splittings were observed. (c) 2006 Elsevier B.V.. All rights reserved.