Properties of the borate ion in dilute aqueous solutions
In this study the viscosity Bη coefficient and the ionic partial molar volume of the borate ion in aqueous solutions have been determined at 25 and 45°C. These properties, together with data reported for the borate mobility, the borate–cation interactions and the formation entropy of the borate ion in aqueous solutions, indicate that B(OH)4 is a “structure-maker”, but its behaviour resembles neither that of a typical strongly hydrated ion (e.g., Li+) nor that of hydrophobic ions.
The partial molar volume and the hydrodynamic radius of the borate ion are close to those corresponding to a rigid sphere having the borate ion crystal radius and bearing a single charge. However, due to its tetrahedrally disposed OH groups it interacts strongly with water molecules but without substantially modifying the bonding pattern present in the solvent.