A complete basis set estimate of cation-π bond strengths: Na+(ethylene) and Na+(benzene)

Large-scale second-order perturbation theory and couple-cluster theory calculations were performed on the Na+(ethylene) and Na+(benzene) complexes in an effort to estimate binding enthalpies in the complete basis set limit. The resulting best estimates are ΔH0[Na+(ethylene)]=−13.6±0.2 kcal/mol and ΔH0[Na+(benzene)]=−24.4±0.3 kcal/mol, which include small corrections for core/valence correlation effects. The former value can be compared to a measurement of −10.3±1.0 kcal/mol obtained from collision-induced dissociation, while the latter value is approximately midway between the two existing experimental values which differ by 6.5 kcal/mol.