Theoretical Study of M+-RG2: (M+ = Ca, Sr, Ba, and Ra; RG = He-Rn)

Ab initio calculations were employed to investigate M+-RG2 species, where M+ = Ca, Sr, Ba, and Ra and RG = He-Rn. Geometries have been optimized, and cuts through the potential energy surfaces containing each global minimum have been calculated at the MP2 level of theory, employing triple-zeta quality basis sets. The interaction energies for these complexes were calculated employing the RCCSD(T) level of theory with quadruple-zeta quality basis sets. Trends in binding energies, D-e, equilibrium bond lengths, R-e, and bond angles are discussed and rationalized by analyzing the electronic density. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are presented. It is found that some of these complexes involving the heavier group 2 metals are bent whereas others are linear, deviating from observations for the corresponding Be and Mg metal-containing complexes, which have all previously been found to be bent. The results are discussed in terms of orbital hybridization and the different types of interaction present in these species.