To assess the role of doubly occupied oxygen 2p orbitals in mediating the magnetic coupling via the superexchange mechanism, the active spaces were expanded to (8,5) for the copper complex, (10,7) for the nickel complex, and (14,11) for the iron complex. These enlarged active spaces were used to assess their influence on the ferromagnetic and antiferromagnetic contributions to the magnetic coupling, within both the CASSCF and the NEVPT2 frameworks.