Boroarsenates:  A Framework Motif and Family Templated on Cations and Anions

Molten salt reactions of NH₄H₂AsO₄, H₃BO₃, and MX (M = Li, Na, K, Rb Cs, NH₄ and X = F, Cl, Br) yield numerous new alkali metal and alkali metal salt templated three-dimensional boroarsenate and fluoroboroarsenate frameworks. The structures of these materials are formed from BO₄ (BO₃F) and As(O,OH)₄ tetrahedra defining channels and interlayer regions containing either simple alkali metal cations or both cations and halide anions. These boroarsenate-based frameworks are unusual in comparison with other oxotetrahedral-based materials in that terminal OH, on As, may be present, decorating the inner surfaces of the channels, as in the 12-membered rings of K₂[B(AsO₃O)₂H]. This unit also permits coordination to nonframework anions as well as cations, so that (Cs₂[BAsO₃OH]₈[AsO₄]₂[CsCl₄]Cl)₂ (and its Br analogue) contains layers of [CsCl₄]^3- and Cl^- ions separated and coordinated by the protonated boroarsenate framework.