Nuclear Magnetic Resonance in B2O3–H2O Glasses and Boric Acids

Abstract

The class of materials B₂O₃–H₂O has been investigated over the range B₂O₃ to B₂O₃·3H₂O. This includes ``dry'' glassy B<sub>2</sub>O<sub>3</sub>, ``wet'' glassy boron oxide of approximate composition B₂O₃·½H₂O, monoclinic and orthorhombic forms of metaboric acid, B₂O₃·H₂O, and triclinic orthoboric acid, B₂O₃·3H₂O. The nuclear quadrupole interaction of the B¹¹ isotope was measured and comparisons of the structures are made on the basis of this interaction. It is shown that all substances contain similar planar BO₃ triangular units. The presence of O–H–O hydrogen bonds, as in B₂O₃·3H₂O, has a minor effect on the boron nuclear quadrupole interaction. It is concluded that BO₄ tetrahedral units exist in several of the wet glass samples as well as in monoclinic metaboric acid.