The first ammoniates of alkali metal fluorides: Cesium fluoride ammonia (3/4) [Cs_3F_3(NH_3)_4] and ammonium cesium difluoride [NH_4CsF_2]

摘要

Two new compounds containing cesium fluoride have been obtained as side-products from the reactions of Cs_2CuF_6 and Cs _2KDyF_6 with liquid ammonia. Cs_2CuF_6 reacts with the solvent forming a still unknown blue substance and the colorless ammoniate Cs_3F_3(NH3)4 which crystallizes in the cubic space group I43d (no. 220) with a = 10.273(1) ? and V = 1084.3(2) ?3 at 123 K with Z = 4. Its crystal structure is isopointal to Y _3Au_3Sb_4 and shows an infinite three-dimensional network made up through N-H?F hydrogen bonds. Ammonium cesium difluoride NH4CsF_2 crystallizes in the orthorhombic space group Pnma (no. 62) with a = 7.1791(1), b = 4.1244(1), c = 13.6417(2) ? andV = 403.92(1) ?3 at 123 K with Z = 4. The crystal structure displays two-dimensional infinite layers of the composition ~2 ∞[(NH_4F _2)-] with embedded Cs~+ ions. Analogous to the structure of the compound Cs_3F_3(NH_3)_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.