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⁻¹nevertheless shows that the He–^tC interactions areantibonding.