Infrared spectra of the ammonium ion in crystals. Part XIII. Crystal structure of (NH₄)₂[AlF₅(H₂O)] and NH₃D⁺ probe-ion spectra in (NH₄)₂[AlF₅(H₂O)], NH₄AlF₄, and (NH₄)₃ZnCl₅, with remarks on structural filiation of AMF₄ fluorides

Abstract

The crystal structure of (NH4)2AlF5•H2O = (NH4)2[AlF5(H2O)] (Pbcn, a = 10.192(4) Å, b = 8.037(2) Å, c = 7.844(1) Å, Z = 4) consists of isolated [AlF5(H2O)]2− octahedral and NH4+ ions. The octahedra are linked by [Formula: see text] bonds to form zigzag chains parallel to c and the chains are cross-linked by normal [Formula: see text] hydrogen bonds to the NH4+ ions. The ir characteristics of the hydrogen bonds in this and the other two title compounds were probed with the NH3D+ ion between 10 and 293 K. The probe-ion spectra confirm the C1 symmetry of the ammonium ion in (NH4)2[AlF5(H2O)] and point to [Formula: see text] bonding of moderate strength. For NH4AlF4 the spectra agree with the expectation from the known crystal structure of both the ordered and the disordered phase, but the transition at ~150 K is not evident in the evolution of the spectra with temperature. Detailed assignment of the ND stretching and bending component absorptions of NH3D+ is not possible for (NH4)3ZnCl5 = (NH4)3(ZnCl4)Cl. However, the unusually low frequencies of two of the components of the ND stretching absorptions in this crystal indicate the existence of [Formula: see text] bonds stronger than those in NH4Cl. The filiation of the known AMF4 structures deriving from TlAlF4 is presented in terms of two-colour space groups.

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2− complex ion in (NH4)2AIF5·H2O single crystals

“…H2O] 2-complex ion, deduced from the fine and SHF structures of the EPR spectrum of Fe 3+ in (NH4)2A1F 5. H20, are confirmed by the X-ray diffraction measurements reported by Knop et al [25]. Thus, we can point out that the EPR method is also very useful for local symmetry studies in a single crystalline material, if the paramagnetic ion is correctly chosen.…”

“…The crystal structure of (NH4)2A1F 5" H20 has been determined for the first time by Knop et al [25]. For the exact identification of the substance, we also identified its crystal structure [24].…”

“…The fact that A is bigger for the two planar fluorines 2 and 4 than that for the other three (1,3,5) is also supported by the crystal structure data obtained with X-ray diffraction methods in ref. 25 …”

Electrochemical Synthesis of Graphite-Tetrafluoroaluminate Intercalation Compounds

“…The uptake of water from the air is another possible factor to contribute to the increase of d i , because AlF 4 − can transform to water−containing species, AlF 4 (H 2 O) l − . 27,29,30 However, considering the high oxidation power of fluoroanion-GICs, this is not very plausible.…”

Diammonium sodium hexafluoroaluminate, (NH4)2NaAlF6

“…The mixture was dissolved in 9 ml distilled water, and heated at 453 K for 7 d under autogenous pressure in a 30 ml Teflon-lined autoclave (ca 30% filled). The title compound was obtained in ca 15% yield (based on Al), with (NH 4 ) 2 AlF 5 (H 2 O) (Knop et al, 1985) also present. Colourless transparent crystals of (NH 4 ) 2 NaAlF 6 , which showed a trigonal trisoctahedron shape, were manually selected under the microscope and used for powder X-ray diffraction.…”