Bonding properties and isomeric conversion pathways from exohedral to endohedral BeGe8 clusters

The B3LYP/6-31G* method was employed to optimize the BeGe8 isomeric structures. Some adsorptive precursors can be formed without experiencing activation energy. Hirshfeld charges and Mayer total valences analysis show that a larger extent of back-donation leading to a higher Be negativity and hypervalency. All Be–Ge bonds are covalent, not ionic, according to charge partitions and M.O. analysis. Cluster energies obtained by the 6-31G* and 6-311++G(3df) basis sets show significant difference and the 6-311++G(3df) energies correlate better with bonding properties. The 6-31G* ground state is a cubic Be@Ge8 that agrees with the literature. However, the 6-311++G(3df) ground state is a cube-distorted C2v Be@Ge8 with less cage strain. The Wade−Mingos rule was added to explain this change. Conversion pathways from the lowest-energetic adsorptive exohedrons to the lowest-energetic endohedrons have been explored and the Mayer bond orders assisted to describe part of the conversion progress.