These results demonstrate the multi-configurational character and strong static electron correlation in these systems, which arise from the degenerate spin orbitals. In addition, the two equally weighted closed-shell singlet configurations are more prominent in the monomer than the OSS configuration, possibly due to the weak coupling between the spin orbitals and the resulting super-exchange interaction, which is insufficient to stabilize the anti-ferromagnetic configuration. Afterwards, NEVPT2 calculations are performed on top of the CASSCF wave functions in order to include the dynamic electron correlations and obtain accurate values for J. The resulting energy difference between the singlet and triplet states of the monomer, J, was calculated to be 460 meV, indicating a very stable triplet ground state (Table ).