Locking water molecules via ternary O-H⋯O intramolecular hydrogen bonds in perhydroxylated closo-dodecaborate

A multitude of applications related to perhydroxylated closo-dodecaborate B₁₂(OH)₁₂^2- in the condensed phase are inseparable from the fundamental mechanisms underlying the high water orientation selectivity based on the base B₁₂(OH)₁₂^2-. Herein, we directly compare the structural evolution of water clusters, ranging from monomer to hexamer, oriented by functional groups in the bases B₁₂H₁₂^2-, B₁₂H₁₁OH^2- and B₁₂(OH)₁₂^2- using multiple theoretical methods. A significant revelation is made regarding B₁₂(OH)₁₂^2-: each additional water molecule is locked into the intramolecular hydrogen bond B-O-H ternary ring in an embedded form. This new pattern of water cluster growth suggests that B-(H-O)⋯H-O interactions prevail over the competition from water-hydrogen bonds (O⋯H-O), distinguishing it from the behavior observed in B₁₂H₁₂^2- and B₁₂H₁₁OH^2- bases, in which competition arises from a mixed competing model involving dihydrogen bonds (B-H⋯H-O), conventional hydrogen bonds (B-(H-O)⋯H-O) and water hydrogen bonds (O⋯H-O). Through aqueous solvation and ab initio molecular dynamics analysis, we further demonstrate the largest water clusters in the first hydrated shell with exceptional thermodynamic stability around B₁₂(OH)₁₂^2-. These findings provide a solid scientific foundation for the design of boron cluster chemistry incorporating hydroxyl-group-modified borate salts with potential implications for various applications.