Metal-free magnetic systems are often characterized by delocalized molecular orbitals, especially for the HOMOs and the lowest unoccupied molecular orbital (LUMO), in contrast to inorganic complexes where atomic orbitals， i.e. d-or forbitals of transition metal elements, dominate the magnetic interactions. To elucidate the magnetic properties of these systems, we performed a comprehensive analysis of the frontier molecular orbitals of the dimers (Figure and Table ). They are, essentially, the superposition of the frontier orbitals of their respective monomers.