The structure of ammonium nitrate (IV)

The crystal structure of phase II ammonium nitrate

“…The two possible orientations for each ion were considered equally probable and hence given equal weight in the Table 2. lnteratomic distances (.4,) and angles (°)for IV-ND4NO 3 (298 K)and II-ND4NO 3 (355 K), with values for IV-NH4NO a (Choi et al, 1972) …”

“…The profile-refinement method was used to analyse the powder diffraction data* obtained for both phase IV (Choi et al, 1972) included for comparison THE CRYSTAL STRUCTURE OF PHASE II AMMONIUM NITRATE and phase II. The least-squares refinement program was that of Rietveld (1969), with modifications by Hewat (1973).…”

“…The crystal structures of all five phases (for the hydrogenous form) have been studied by X-ray diffraction, but only the room-temperature phase IV has been satisfactorily determined; this was by singlecrystal neutron diffraction (Choi et al, 1972). The direct transformation of phase IV to phase II has been the subject of several studies and a proposed structure for phase II from X-ray diffraction has been reported by Shinnaka (1956).…”

“…Five distinct phases with reversible transitions between them in the sequence V-IV-III-II-I have been reported (Nagatani, Seiyama, Sakiyama, Suga & Seki, 1967). At room temperature, phase IV has an orthorhombic crystal structure (Choi, Mapes & Prince, 1972), which transforms to a tetragonal phase V structure (Amor6s, Arrese & Canut, 1962) when cooled below 255 K. On heating above room temperature, transitions occur to an orthorhombic phase III structure at 305.3 K (Goodwin & Whetstone, 1947), a tetragonal phase II structure at 357 K (Shinnaka, 1956) and to a cubic phase I structure above 398 K (Shinnaka, 1959a). Dry crystals (without occluded water) have been found to transform directly from the phase IV structure to phase II on heating at 328 K (Brown & McLaren, 1962).…”

The crystal structure of calcium ammonium hydrogenpyrophosphate CaNH4HP2O7

“…Table 4 gives distances and angles associated with the hydrogen bonds. There is no disorder of NH 4 groups; the N-H...O hydrogen-bond lengths are fairly typical of those observed in ammonium salts (Hamilton & Ibers, 1968;Choi, Mapes & Prince, 1972 (Novak, 1973) for the double-minimum type hydrogen bond, H(1) refined to a location much closer to 0(6) ( Table 3). Both H(1) and H(2) were treated the same way in the refinement and thus the two hydrogen bonds must be quite different.…”