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.