A critical evaluation of the experimental and theoretical determination of lithium cation affinities

A comprehensive comparison of multiple levels of theory with experimental values for about thirty lithium cation affinities (LCAs) is conducted. The experimental values are largely taken from threshold collision-induced dissociation (TCID) measurements augmented with equilibrium measurements from ion cyclotron resonance experiments. Possible reasons for errors in the experimental TCID results are explored. An examination of the theoretical results reveals that core correlation on the lithium ion(Li-C) is needed to accurately describe these complexes. Several procedures for assessing complete basis set (CBS) extrapolations from MP2(full)/aug-cc-pVnZ(Li-C)//MP2(full)/cc-pVDZ(Li-C), n = D, T, and Q, calculations are completed and compared to experiment and lower levels of theory. It is found that LCAs calculated using CBS methods including core correlation are higher than most other methods and generally in good agreement with experimental values. Because the CBS approach requires use of the computationally intensive aug-cc-pVQZ(Li-C) basis set, we recommend that an adequate level of theory is provided by a MP2(full)/aug-cc-pVTZ(Li-C)//MP2(full)/cc-pVDZ(Li-C) approach excluding basis set superposition errors. Given these theoretical results, discrepant experimental values in the literature for several lithium ion complexes are evaluated.