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Topological Analysis of Electron Densities: Is the Presence of an Atomic Interaction Line in an Equilibrium Geometry a Sufficient Condition for the Existence of a Chemical Bond?



The structure, energetics, and electron density in the inclusion complex of He in adamantane, C10H16, have been studied by density functional theory calculations at the B3LYP6-311++G(2p,2d) level. Topological analysis of the electron density shows that the He atom is connected to the four tertiary tC atoms in the cage by atomic interaction lines with (3,−1) critical points. The calculated dissociation energy of the complex He@adamantane(g)=adamantane(g) + He(g) of ΔE=−645 kJ mol−1 nevertheless shows that the He–tC interactions are antibonding.