An infrared spectroscopic and Ab initio investigation of aqueous boric acid solutions: Evidence for the structure and transformation of the polyboric acid molecules

Boric acid is the common species in borate chemistry and is widely found in nature and Salt Lake brines. It undergoes polymerization reactions to form a variety of borate minerals. However, there are few reports on the polymerization reaction of boric acid molecules in solution to generate polymeric boric acid molecules. In this work infrared spectroscopy technology and quantitative calculation methods were used to study the structure and interconversion of polymeric boric acid molecules in boric acid solution. Research shows that boric acid molecules, six-membered cyclic triboric acid molecules, and ring-chain tetraboric acid molecules exist in boric acid solutions, and as the concentration of the solution increases, these species undergo polymerization reactions and mutual transformations; high degree of polymerization boric species such as bicyclic tetrameric boric acid molecules and pentameric boric acid molecules don't exist in boric acid solutions; Chain dimer boronic acid molecules does not detected in the infrared spectrum. This work provides a new understanding of boron-containing species and their mutual transformation in boric acid solution.