Calculations of the Lu ₃ N@C ₈₀ two-isomer equilibrium

Computations of the relative concentrations are reported for the two isomers of Lu ₃ N@C ₈₀ experimentally known, i.e., produced by encapsulation into the isolated-pentagon-rule (IPR) C ₈₀ cages with I _h and D _5h symmetries. The calculations are mostly based on the density-functional theory (DFT) treatments with the B3LYP functional. The inter-isomeric energetics is further refined with the MP2 perturbation method which places the (Formula presented.) endohedral higher in the potential energy by 16.9 kcal/mol. The isomeric populations are evaluated using the Gibbs energy in a broad temperature interval. The computations performed with the floating-encapsulate-model (FEM) treatment can reasonably reproduce the observed isomeric ratio, thus pointing out a need for adequate representation of the dynamic endohedral symmetry.