Borate materials in which boron is bonded exclusively to oxygen have attracted attention due to their rich crystal chemistry and uses in current and emerging applications related to energy, urbanization and agriculture. From a structural viewpoint, boron in these materials can be tri- or tetra-coordinated, forming BO3 and BO4 units that may link via oxygen corner sharing to form rings, cages, chains, sheets and networks. This paper presents recent studies on sodium enneaborate, 2 Na2O ● 9 B2O3 ● 11 H2O, a known and never fully characterized phase in Na2O-B2O3-H2O phase diagram. Similarly an ammonium octaborate was structurally characterized for the first time revealing it to be the ammonium salt of the ribbon isomer of the heptaborate anion, B7O9(OH)5 2−, with included boric acid and water molecules. This compound forms spontaneously at room temperature in solid state mixtures of ammonium tetraborate and ammonium pentaborate or from boric acid and ammonia in appropriate stoichiometric ratios. It crystallizes in the monoclinic space group P21/c with well-ordered ammonium cations and B7O9(OH)5 2− anions and disordered B(OH)3 and H2O molecules linked by extensive H-bonding.

Synthesis, structures and properties of some recently characterized borates

2019 Fall National Meeting

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