The electronic coupling strength between the fragment orbitals in the dimers can be quantified by the hopping or transfer integral (Table ). This can be approximated by the HOMO-LUMO gap of the dimer (Figure ): Egap= 2t. In addition to the OSS ground state, the high-spin and closed-shell states are also required, as their energy difference indicates the strength of the electronic correlation in spin-dimer systems, which is related to the on-site Coulomb repulsion term, U, in the Hubbard model (Figure ). In general, according to the Goodenough-Kanamori rule, the magnetic coupling J is dominated by both potential exchange and kinetic exchange, as formulated by