Dihydrogen Bonds in Aqueous NaBD4 Solution by Neutron and X-ray Diffraction.

Neutron diffraction, X-ray diffraction, and empirical potential structure refinement modeling were employed to study the structure of alkaline aqueous NaBD4 solutions at different NaBD4 concentrations and temperatures. In 1.0 mol·dm-3 NaBD4 aqueous solutions, about 5.6 ± 1.6 water molecules bond to BD4- via tetrahedral edges or tetrahedral corners without a very specific hydration geometry; that is, each hydrogen atom of BD4- bonds to 2.2 ± 1.0 water molecules through dihydrogen bonds with the D(B)···D(W) distance of 1.95 Å. The number of dihydrogen bonds decreases with increasing concentration and increases with temperature. Dihydrogen bonding is a predominantly electrostatic interaction which shows relatively lower directionality and saturability in comparison with the regular hydrogen bonds between water molecules. The water orientation around BD4- shows that the proportion of tetrahedral-edge dihydrogen bonds increases with temperature and decreases with concentration.