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 Cs 2 CuF 6 and Cs 2 KDyF 6 with liquid ammonia. Cs 2 CuF 6 reacts with the solvent forming a still unknown blue substance and the colorless ammoniate Cs 3 F 3 (NH 3 ) 4 which crystallizes in the cubic space group I43d (no. 220) with a = 10.273(1)Å and V = 1084.3(2)Å 3 at 123 K with Z = 4. Its crystal structure is isopointal to Y 3 Au 3 Sb 4 and shows an infinite three-dimensional network made up through N-H···F hydrogen bonds. Ammonium cesium difluoride NH 4 CsF 2 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)Å 3 at 123 K with Z = 4. The crystal structure displays two-dimensional infinite layers of the composition 2 ∞ [(NH 4 F 2 ) − ] with embedded Cs + ions. Analogous to the structure of the compound Cs 3 F 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.

Identifying the Gate-Opening Mechanism in the Flexible Metal–Organic Framework UTSA-300

“…The strengths of the H-bond C–H···F are calculated to be 8.297, 9.166, and 10.131 kJ/mol, respectively, for F–H distances of 2.311, 2.287, and 2.264 Å in pristine UTSA-300a, which reflect their typical moderate values. , The first C 2 H 2 molecule adsorbs on the F atom almost linearly subtending an angle F–H–C of 175.8° at a distance of 1.953 Å (see Figure a) and 1.982 Å from F of another ZnSiF 6 chain. The short distance below 2.0 Å is rare in F–H bonds and, here, it is due to a strong interaction between sp 1 hybridized C of C 2 H 2 and the electronegative F atom that offers an electrostatic component as evidenced by the directional bonding. The adsorption geometry agrees with one of the adsorption sites reported in ref , but our simulations do not support the presence of a secondary binding site with close binding energy.…”

“…71,72 The first C 2 H 2 molecule adsorbs on the F atom almost linearly subtending an angle F−H−C of 175.8°at a distance of 1.953 Å (see Figure 5a) and 1.982 Å from F of another ZnSiF 6 chain. The short distance below 2.0 Å is rare in F−H bonds 73 and, here, it is due to a strong interaction between sp 1 hybridized C of 2, we can also see that between the loading of three and four C 2 H 2 molecules, there is a cross-over, and the UTSA-300 structure is now energetically preferred over the UTSA-300a structure.…”