In the framework of steric effects, we can establish that a relatively larger volume of fullerenes (C36, C40, C44) would cause a larger steric repulsion at shorter intermolecular distances in the second class of complexes. In this manner, intermolecular distances slightly increase (dinter2.1-2.2 Å) to compensate for the volume exclusion effects when fragments are brought into close interaction. As a result, the strong stabilization gained by short-range contributions decay and weak long-range EELEC and EDISP effects compensate the steric destabilization; consequently, lower adsorption energies are reached compared to the first class of covalent complexes (Fig. ).