LAUSR

The effect of substitution in the dodecahedrane (C20H20) cage on bonding in the confined He dimer is analyzed. The HeHe distances inside the halogenated dodecahedrane C20X20 (X = FBr) cages are found to be less than half of that in the free He dimer. Comparing the equilibrium structure of He2@C20H20 with He2@C20X20 at ωB97XD/def2‐TZVPP level, it is found that the He‐He distances are relatively larger in the latter cases indicating the influence of halogen groups on the interaction between the cage and the trapped He pair. The viability of the He2@C20X20 complexes is reflected in the presence of a very high activation energy barrier against the thermochemically feasible dissociation process producing free He2 and C20X20. Quantum theory of atoms in molecules (QTAIM) approach reveals a partial covalent interaction between He pair.