Super Strong Be-Be Bonds: Theoretical Insight into the Electronic Structure of Be-Be Complexes with Radical Ligands

The electronic structure of complexes formed by the interaction of Be₂ with radical ligands (L:Be-Be:L) has been studied by means of the high-level theoretical protocol CCSD(T)/cc-pVTZ. At this level of theory, no matter the nature of the ligand, the Be-Be bond becomes up to 300 times stronger compared to isolated Be₂, indicating that these kinds of complexes are thermodynamically stable and, thus, that they could be experimentally detected. Moreover, among all of the ligands considered, the strength of the Be-Be bond for L = [CN]^• was calculated to be 330 kJ·mol^-1, slightly greater than the strongest up to date L = F^• complex, thus setting a new mark for the strongest Be-Be bond reported so far in the literature. Wave function analysis methods explain this strong interaction as a result of the oxidation of the Be₂ moiety to Be₂²⁺ due to charge transfer toward the L ligands. In this study, we have also considered F:Mg-Mg:F complexes, which show very similar properties as the ones described for the analogous F:Be-Be:F.