Strong Be–Be Covalent Bond in Be2L2 and Na2Be2L2 Molecules with Cyano-Based Ligands

The stabilization effect of some known cyano-based ligands (L = thiocyanate, dicyanamide, tricyanomethanide, tetracyanoborate, and pentacyanocyclopentadienide) on the Be–Be bond is investigated. The evaluated electronic energy changes for different dissociation channels show that Be2L2 molecules have high thermodynamic stability. Dissociation energies of the Be–Be bonds in the mentioned molecules are in the range 71–77 kcal mol–1. Different bonding analyses indicate the covalent nature of the Be–Be bond in these structures. Additionally, the effect of sodium atoms on the Be–Be bond length in these molecules is studied. The obtained results confirmed that although the Be–Be bond is also formed in Na2Be2L2 molecules, the Be–Be bond lengths in Na2Be2L2 structures are smaller than those observed in Be2L2 molecules. Based on the generalized Kohn–Sham energy decomposition analysis, the Be–Be bond formation in the presence of cyano-based ligands is mainly due to both electrostatic forces and polarization effects. Bonding analysis verified that the Be–Be bond in Be2L2 structures is a σ-bond, while the π-character has more contribution in the Be–Be bond of Na2Be2L2 molecules. These studies show that the selected ligands have significant effects on the strengthening of Be–Be bonds in both Be2L2 and Na2Be2L2 molecules.