Hydrolysis mechanism of the cyclohexaborate anion: Unraveling the intricacies

B6O7OH62-$$ {\mathrm{B}}_6{\mathrm{O}}_7{\left(\mathrm{OH}\right)}_6<^>{2-} $$ is a highly polymerized borate anion of three six-membered rings. Limited research on the B6O7OH62-$$ {\mathrm{B}}_6{\mathrm{O}}_7{\left(\mathrm{OH}\right)}_6<^>{2-} $$ hydrolysis mechanism under neutral solution conditions exists. Calculations based on density functional theory show that B6O7OH62-$$ {\mathrm{B}}_6{\mathrm{O}}_7{\left(\mathrm{OH}\right)}_6<^>{2-} $$ undergoes five steps of hydrolysis to form H3BO3 and BOH4-$$ \mathrm{B}{\left(\mathrm{OH}\right)}_4<^>{-} $$. At the same time, there are a small number of borate ions with different degrees of polymerization during the hydrolysis process, such as triborate, tetraborate, and pentaborate anions. The structure of the borate anion and the coordination environment of the bridging oxygen atoms control the hydrolysis process. Finally, this work explains that in existing experimental studies, the reason for the low B6O7OH62-$$ {\mathrm{B}}_6{\mathrm{O}}_7{\left(\mathrm{OH}\right)}_6<^>{2-} $$ content in solution environments with low total boron concentrations is that it depolymerizes into other types of borate ions and clarifies the borate species. The conversion relationship provides a basis for identifying the possibility of various borate ions existing in the solution. This work also provides a certain degree of theoretical support for the cause of the "dilution to salt" phenomenon. Borate ions with different degrees of polymerization in salt lakes continue to undergo transformation processes such as hydrolysis and polymerization. This picture reflects the specific process of hydrolysis of cyclic hexaborate ions in this article and the recycling process of the ultimately generated boric acid molecules. This has theoretical guiding significance for the separation of boron resources in the lithium extraction process during the development of salt lake resources. image