First, the stability of covalent complexes (Phos-C24 to Phos-C44) emerges from the charge-transfer term (ECT) because of the strong orbital interactions with a contribution of 38-48% to the stabilizing energy (Fig. ), agreeing with the high magnitude of electron transfer in the covalent complexes (Table ). The second highest contribution to the stability emerges from polarization effects as expected in short-range orbital interactions (EPOL, up to 32%). The latter denotes strong intramolecular charge rearrangements due to the on-fragment relaxation of each species to the presence of the nuclei and electrons of all other fragments. Then, covalent bonding is demonstrated from the physical viewpoint. It is worth mentioning that an obvious correlation between the number of transferred electrons and ECT magnitude cannot be established because ECT term also accounts for energy lowering associate with intramolecular electron flow, allowing to delocalize electrons over the complex. The latter explains why the ECT contribution is high in Phos-C24 (43%) in spite that the whole intermolecular charge transfer is low (0.08|e|, Table ), which could be caused by strong intrafragment electron density rearrangements and bond polarization in the [4+4]-cycloaddition as noted from the high EPOL contribution (32%).