Polyborates in aqueous borate solution: A Raman and DFT theory investigation

The geometries, energies and vibrational frequencies of various polyborates in both gaseous and aqueous phase were calculated at the B3LYP/aug-cc-pVDZ level. The calculated total symmetrical stretching Raman shifts of B(OH)3, B(OH)4−, B2O(OH)4, B2O(OH)5−, B2O(OH)62−, B3O3(OH)3, B3O3(OH)4−, B3O3(OH)52−, B3O3(OH)63−, B4O5(OH)42− and B5O6(OH)4− were assigned to 877.40, 735.33, 785.22, 792.90, 696.79, 587.72, 599.06, 740.16, 705.01, 551.67 and 521.04 cm−1, respectively. The results can be used as the characteristic frequency for polyborates in aqueous phase at room temperature. At least six types of polyborates B(OH)3, B(OH)4−, B3O3(OH)4−, B3O3(OH)52−, B4O5(OH)42− and B5O6(OH)4−, occur in aqueous solutions at ambient temperature. The chemical species distribution and the relevant interaction mechanisms among polyborates in the solutions were also suggested.

. The calculated symmetrical stretching vibration (νs) Raman shifts of polyborates can be used as the characteristic frequencies of polyborates in aqueous phase. At least six polyborates B(OH)3, B(OH)4−, B3O3(OH)4−, B3O3(OH)52−, B4O5(OH)42− and B5O6(OH)4− exist in aqueous borate solutions.Figure optionsDownload as PowerPoint slideHighlights
► Raman shifts of 11 aqueous polyborates were calculated by DFT.
► The results coincide with Raman spectrum of aqueous H3BO3, NaBO2, K2B4O7 and NaB5O8.
► Characteristic frequencies of polyborates in aqueous phase were summed.
► Chemical species distribution and interaction mechanism of polyborates were inferred.