Structural and Bonding Analyses on a Homologous Metal–Metal Bond Guest–Host Series M2@C50X10 (M = Zn, Cd, Hg; X = CH, N, B)



A systematic density functional study was performed on the structures and bonding features in a homologous metal–metal (M–M) host–guest series M2@C50X10 (M = Zn, Cd, Hg; X = CH, N, B). Calculations indicated that D5d conformers are energy minima for Zn2@C50X10 (X = CH, N) and Cd2@C50X10 (X = CH, N, B), whereas Zn2@C50B10 has no imaginary frequency with the lowered C2h symmetry. Among these hybrid fullerene–metal complexes, those with dizinc and dicadmium guests adopt η55 coordination, except for an η22 case in C2h-Zn2@C50B10, to meet appropriate interactions between the metal atom and cage; and the η11 coordination mode can only be satisfied in just one (Hg2@C50N10) of the complexes with Hg–Hg guests, regardless of the enforced coordination surroundings. The nature of metal–cage interactions between M22+ and C50X102– moieties and M–M bonds have been analyzed by means of the topological properties of electron densities and energy-partitioning methods, and results suggest that the two types of interactions are almost similar to those in their M2(C5H5)2 counterparts.