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

Abstract

A multitude of applications related to perhydroxylated closo-dodecaborate B₁₂(OH)₁₂²⁻ in the condensed phase are inseparable from the fundamental mechanisms underlying the high water orientation selectivity based on the base B₁₂(OH)₁₂²⁻. Herein, we directly compare the structural evolution of water clusters, ranging from monomer to hexamer, oriented by functional groups in the bases B₁₂H₁₂²⁻, B₁₂H₁₁OH²⁻ and B₁₂(OH)₁₂²⁻ using multiple theoretical methods. A significant revelation is made regarding B₁₂(OH)₁₂²⁻: 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 B₁₂H₁₂²⁻ and B₁₂H₁₁OH²⁻ 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)₁₂²⁻. 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.