Structure of aqueous potassium metaborate solution

•Study shows that the main borate species in aqueous KB(OH)4 solutions is B(OH)4−.•The average hydration number of the first hydration shells of K+ is 8.1 and the hydration distance is ∼0.294 nm.•The B–O(H2O) distance in hydrated anion B(OH)4− is about 0.37 nm with an average hydrated number of 2.3.•Contact ions KB(OH)40 exist in KB(OH)4 solutions, the distance of K–B is about 0.34 nm.•Concentration and temperature also effect the hydration structure of B(OH)4.

The structure of aqueous potassium metaborate solutions has been confirmed by X-ray scattering, Raman spectra and species distribution calculation. The optimized structure of B(OH)4− was obtained by density functional theory calculation. The hydration distance and hydration number of K+ in aqueous potassium metaborate solution were given by X-ray scattering. The B–O(H2O) distance in hydrated anion B(OH)4− were determined to be 0.37 nm with the hydration number of 2.3 per hydroxyl(–OH). The K–B distance of the contact ions KB(OH)40 was measured to be 0.34 nm.