The potassium fluoride–boric acid system. Hydrogen bonding in KF·H3BO3

Abstract

Ab initio LCAO–MO–SCF calculations have been performed on the most likely interactions between F– and H3BO3. These show that the monofluoroborate ion [BF(OH)3]- is the most stable, but only by 33 kJ mol–1 relative to the hydrogen-bonded system F–⋯ HOB(OH)2. Infrared analysis of the solid phase of composition KF.H3BO3, which grows from an aqueous solution of KF and H3BO3, shows the hydrogen-bonded structure to be the preferred form. The results of 19F and 11B n.m.r. studies on aqueous solutions of KF and H3BO3 are also consistent with hydrogen bonding being the chief interaction although it is possible that an equilibrium exists involving [BF(OH)3]– since [BF3(OH)]– is detectable in such solutions.