Influences of alkali and alkaline-earth metal ions on the geometric structure, electronic properties and reactivity of B₉N₉ ring

Structures, electronic structures, UV-Vis spectra and orbital transition characteristics, electrophilic and nucleophilic reactivities, thermodynamic properties of B₉N₉@Mⁿ⁺ (Mⁿ⁺ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ and Ca²⁺) have been investigated based on calculations at ωB97XD/def2-TZVP level and TD (time dependent) – ωB97XD/def2-TZVP level. The calculation results indicate that compared to alkali metal ions, alkaline earth metal ions can increase deformation degree of B₉N₉ ring, charge separation degree, red-shift maximum absorption peak position (λ_max), enhance electrophilic and nuclophinic reaction performances, enhance binding abilities and binding constants between B₉N₉ ring and metal ions. In one word, alkaline earth metal ions have stronger regulatory effects than alkali metal ions in all the involved B₉N₉@Mⁿ⁺ species. Based on this work, complexes between B₉N₉ ring and alkaline earth metal ions may have better performances in adsorption of organic small molecules and inorganic ions, and these complexes may be potential efficient absorbents due to their very negative local electron attachment energies.