Speciation of borate in aqueous solutions studied experimentally by potentiometry and Raman spectroscopy and computationally by DFT calculations

The speciation of borate has been studied by potential titration in 0.5 M NaClO4 and Raman spectroscopic titration at 25 °C. Five borate species including B(OH)4−, B3O3(OH)4−, B5O6(OH)4−, B3O3(OH)52−, and B4O5(OH)42− along with boric acid, H3BO3, are identified, and the corresponding formation constants are determined accordingly in the solutions with initial boron concentrations between 0.01 and 0.7 M. The attributions for the Raman shifts of the spectra at 874 cm−1 to the ν1 vibrational mode of B(OH)3, 741 cm−1 to ν1 of B(OH)4−, 610 cm−1 to ν1 of B3O3(OH)4−, 525 cm−1, 760 cm−1, 915 cm−1, and 994 cm−1 to ν1, ν2, ν4, and ν3 of B5O6(OH)4−, 612 cm−1 to ν1 of B3O3(OH)52−, and 563 cm−1 (ν1a) and 938 cm−1 (ν1b) to B4O5(OH)42− are made by combining the speciation from potential titrations and deconvolution of Raman spectra with DFT calculations.