Describing Noble Gas and Group 13 Hypercoordinated Bonds through the Overlap Electron Density

This work investigates the nature of the bonding between noble gases and Group 13 elements in hypercoordinated systems using overlap electron density descriptors derived from the OP/TOP model. Density Functional Theory (DFT) calculations were performed to analyze the overlap electron density changes across the H₄E–Ng series (E = Al–Tl; Ng = He–Rn) at the ωB97X-D3/def2-TZVP level of theory. The results demonstrate that the overlap electron density of the E–Ng bond increases with the atomic number of the noble gas and decreases as the atomic radius of the Group 13 element increases. Previous studies have shown that the covalent character of the E–Ng bond governs the stability of these complexes through the charge-transfer (CT) effect. Our findings demonstrate that the orbital overlap correlates well with the CT contribution, providing complementary information about the nature of these unusual chemical bonds.