The First Ammoniates of Alkali Metal Fluorides: Cesium Fluoride Ammonia (3/4) [Cs3F3(NH3)4] and Ammonium Cesium Difluoride [NH4CsF2]

Abstract

Two new compounds containing cesium fluoride have been obtained as side-products from the reactions of Cs2CuF6 and Cs2KDyF6 with liquid ammonia. Cs2CuF6 reacts with the solvent forming a still unknown blue substance and the colorless ammoniate Cs3F3(NH3)4 which crystallizes in the cubic space group I 4̄3d (no. 220) with a = 10.273(1) Å and V = 1084.3(2) Å3 at 123 K with Z = 4. Its crystal structure is isopointal to Y3Au3Sb4 and shows an infinite three-dimensional network made up through N-H· · ·F hydrogen bonds. Ammonium cesium difluoride NH4CsF2 crystallizes in the orthorhombic space group Pnma (no. 62) with a = 7.1791(1), b = 4.1244(1), c = 13.6417(2) Å and V = 403.92(1) Å3 at 123 K with Z = 4. The crystal structure displays two-dimensional infinite layers of the composition 2 ∞[(NH4F2)−] with embedded Cs+ ions. Analogous to the structure of the compound Cs3F3(NH3)4, the structural motif is formed through strong N-H· · ·F hydrogen bonds, which seem to be the guiding force. To the best of our knowledge, the title compounds are the first reported ammoniates of alkali metal fluorides.