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

Area of Science:

• Solution Chemistry
• Physical Chemistry
• Materials Science

Background:

• Understanding the hydration structure of ions is crucial for chemical processes.
• Sodium borohydride (NaBD₄) solutions are used in various chemical applications.
• The role of dihydrogen bonding in aqueous solutions requires further investigation.

Purpose of the Study:

• To investigate the structure of alkaline aqueous NaBD₄ solutions.
• To determine the hydration geometry and bonding interactions of the borate anion (BD₄⁻).
• To analyze the influence of concentration and temperature on these interactions.

Main Methods:

• Neutron diffraction
• X-ray diffraction
• Empirical potential structure refinement modeling

Main Results:

• In 1.0 mol·dm⁻³ NaBD₄ solutions, approximately 5.6 water molecules interact with BD₄⁻.
• Each hydrogen atom of BD₄⁻ forms about 2.2 dihydrogen bonds with water molecules.
• Dihydrogen bond count decreases with concentration and increases with temperature, with higher tetrahedral-edge bonding at elevated temperatures.

Conclusions:

• Dihydrogen bonding in NaBD₄ solutions is primarily electrostatic, with lower directionality than water-water hydrogen bonds.
• Temperature and concentration significantly affect the number and geometry of dihydrogen bonds.
• The findings provide insights into the hydration dynamics of the borate anion in aqueous media.