The theoretical calculations on magnetic exchange of the title complex are carried out by using multiconfigurational second-order perturbation theory, CASPT2, and density functional theory combined with broken-symmetry approach, DFT-BS. The CASPT2 calculated quartet ground state, stabilized by 8.02 cm(-1) compared with the nearest excited doublet state, is close to 5 cm(-1) of the experimental measurement. The dependence of energy levels on the ratio J(23)/J(12,13) validates occurrence of the spin frustration I phenomenon. Both CASPT2 and DFT-BS calculations reproduce well experimentally coupling constants of J(12,13) = -9.35 cm(-1), = -3.95 cm(-1), for CASPT2 J(12,13) = -6 cm(-1), J(23) = -2 cm(-1) and for DFT-BS J(12,13) = -11.31 cm(-1), J(23) = -4.20 m(-1). The methodological comparison is briefly discussed. © 2005 Elsevier B.V. All rights reserved.