Mechanism for hydrolysis of double six-membered ring tetraborate anion

摘要

[B4O5(OH)(4)(2-)] is a representative borate anion with a double six-membered ring structure, but there is limited knowledge about the hydrolysis mechanisms of [B4O5(OH)(4)(2-)]. Density functional theory-based calculations show that the tetraborate ion undergoes three-step hydrolysis to form [B(OH)(4)(-)] and an ring intermediate, [B3O2(OH)(6)(-)]. Other new structures, such as linear trimer, branched tetraborate, analogous linear tetraborate, are observed, but they are not stable in neutral systems and change to ring structures. [B3O2(OH)(6)(-)] hydrolyzes to [B(OH)(4)(-)] and [B(OH)(3)] in the last two steps. The structure of borate anion and the coordination environment of the bridge oxygen atom control the hydrolysis process. [B4O5(OH)(4)(2-)] always participates in the hydrolysis reaction, even with a decrease in concentration. [B3O3(OH)(4)(-)], [B(OH)(4)(-)], and [B(OH)(3)] have different roles in "water-poor" and "water-rich" zones. Concentration and pH of solution are the key factors that affect the distribution of borate ions.