Binding Enthalpies for Alkali Cation−Benzene Complexes Revisited

The geometries and binding enthalpies of M + (benzene) complexes (M = Li, Na, K, Rb, and Cs) were obtained from large basis set second-order perturbation theory and coupled cluster theory calculations. The best Δ H 298 estimates (in kcal/mol) are Li + (benzene) = −36.8 ± 0.2 (theory) vs −37.9 and −39.3 ± 3.2 (expt), Na + (benzene) = −24.7 ± 0.3 (theory) vs −28.0 ± 1.5 and −22.5 ± 1.5 (expt), K + (benzene) = −20.1 ± 0.4 (theory) vs −19.2 and −17.1 ± 0.9 (expt), Rb + (benzene) = −16.4 ± 0.2 (theory) vs −16.4 ± 0.9 (expt), and Cs + (benzene) = −12.5 ± 0.2 (theory) vs −15.1 ± 1.1 (expt). The present findings include small corrections for core/valence correlation effects and lead to binding enthalpies uniformly larger than those of previous theoretical studies.