The structural elucidation of aqueous H 3 BO 3 solutions by DFT and neutron scattering studies.

The micro-structure of aqueous boric acid (H3BO3) solutions is of broad interest in earth sciences, geochemistry, material science, as well as chemical engineering. In the present study, the structure of aqueous H(3)BO(3)solutions was studiedvianeutron scattering with(2)H and(11)B isotope labelling combined with empirical potential structure refinement (EPSR) modelling. In aqueous H(3)BO(3)solutions, B(OH)(3)is the dominant borate species. Density function theory (DFT) calculations show that the boron hydroxyl has a lower electrostatic potential (ESP), which makes B(OH)(3)a relatively weakly hydrated, compared with the bulk water. In the 0.95 mol L(-1)H(3)BO(3)solution at 298 K (saturated), similar to 18 water molecules enter the hydration sphere of B(OH)(3)with the hydration distance (B-O(W)) of 3.75 angstrom, while only 4.23 of them hydrate with H(3)BO(3)as the hydrogen bond (H-bond) acceptor or H-bond donor. Both neutron scattering and DFT calculations for 2B(OH)(3)center dot 6H(2)O clusters at the omega B97XD/6-311++g(3df,3pd) basis level show that B(OH)(3)forms molecular clusters in bidentate contact molecular pairs (BCMP), mono-dentate molecular pairs (MCMP), solvent-shared molecular pairs (SMP), and parallel solvent-shared molecular pairs (PSMP) in aqueous solutions. Their relative contents are both concentration- and temperature-sensitive. BCMP with the B-B distance of similar to 4.1 angstrom is the dominant molecular pair in the aqueous solutions. Relatively less content and van der Waals interactions stabilized PSMP, with a B-B distance of similar to 3.6 angstrom between the two parallel layers, which is a crucial species for the crystallization of H(3)BO(3)from aqueous solution.