Theoretical Study of the Microsolvation of the Leapfrog Generated B18 in Water : B18-Solvent vs. Solvent–Solvent Interactions

This study presents a theoretical investigation of the solvation behavior of the leapfrog-generated B 18 cluster in water, employing the M06-2X density functional with the 6-31+G(d, p) and 6-311+G(3df,2p) basis sets. Both SMD implicit solvation and explicit microsolvation models were applied to B 18 (H 2 O) n ( n = 0–10). Our results reveal that solvation is governed by the interplay between solute–solvent and solvent–solvent interactions. In aqueous solution, structured hydrogen-bond (O-H…O) networks emerge, with water–hydronium interactions dominating the solvent–solvent component, while solute–solvent stabilization is primarily driven by strong electrostatic interactions between [B 18 (OH) 2 ] 2- and hydronium ions, H 3 O + . Energy decomposition analysis shows that stabilization is largely controlled by pairwise interactions, supported by moderate cooperative effects, with minimal higher-order many-body contributions. Solvating bare B 18 with water promotes spontaneous O–H bond cleavage, yielding hydroxylated species and enabling proton transfer, a reactivity also seen in NH 3 –B 18 adducts. Overall, stabilization arises predominantly from localized electrostatic, polarization, and hydrogen-bonding interactions within a compact first solvation shell rather than long-range collective phenomena. Detailed bonding analysis confirms that the B–O bonds are highly stable, polarized covalent σ-bonds with partial π-back donation, imparting multiple-bond character and reducing boron’s electron deficiency.