Structures and Stabilities of Endo- and Exohedral Dodecahedrane Complexes (X@C_(20)H_(20) and XC_(20)H_(20), X = H~+, H, N, P, C~-, Si~-, O~+, S~+)

摘要

B3LYP/6-31G~* computations predict the relative energies and stabilities of the endohedral (X@C_(20)H_(20)) and exohedral (XC_(20)H_(20)) dodecahedrane complexes (X = H~+, H, N, P, C~-, Si~-, O~+, S~+). H~+ does not bind endohedrally but bridges a C-C bond exohedrally; the proton affinity is 185.3 kcal/mol. Except for O~+, all other guest species (H, N, P, C~-, Si~-, S~+) are minima at the cage center. The H-atom inclusion energy is similar to that of helium (36.3 vs 38.0 kcal/mol), whereas the other endohedral complexes have much higher inclusion energies (125-305 kcal/mol). In all cases, the endohedral complexes are energetically less favorable than their exohedral isomers. C_(20)H_(21) has a cage-ruptured structure, whereas N, P, and their isoelectronic analogues have exohedral structures and bind as doublet states to broken cage C-C bonds. Endohedral H, N, C~-, O~+, and S~+ preserve their unencapsulated ground states, whereas P and Si~- interact strongly with the cage and lose their atomic ground-state character.