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.