The Creutz-Taube complex [(NH3)(5)-Ru-pyrazine-Ru-(NH3)(5)](5+) is studied using wave function-based methods, namely the CASSCF/MS-CASPT2 method. Spin-orbit effects have been calculated with the SO-RASSI program. The nature of the ground state is analyzed, and all the excited states up to 50 000 cm(-1) are calculated. They form a quasi continuum from 25 000 cm(-1), theoretical bands are assigned to UV-visible spectra, and MCD bands are assigned by calculating transition moments from first principles for both spectroscopies. g-Factors are calculated from first principles and modeled by a model Hamiltonian: they compare well to experimental values and are shown to be the same as in the monomeric species.