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Accurate integrated intensities for the Bragg reflection of neutrons from a ZnS single crystal have been measured at temperatures between 285 and 1173 K. After correction for thermal diffuse scattering and extinction effects the data were interpreted with different models that allow anharmonic contributions to the temperature factor. Both the cumulant expansion and the one‐particle potential (OPP) model with quasiharmonic temperature dependence describe the data satisfactorily, although the Gruneisen parameter obtained in the OPP analysis differs greatly from the value calculated from known thermodynamic quantities. Predictions based on Matsubara’s anharmonic formalism are not in accord with the behavior observed at the highest temperatures.

Neutron diffraction studies have been performed on layered sodium trideuterium selenite Na(H0.06D0.94)3 (SeO3)2 in both the paraelectric and the ferroelectric phases. The crystal data are a = 10.365(2), b = 4.850(1), c = 5.792(1) A, β = 91.16(3)°, Z = 2, space group P21/n for the paraelectric phase at 298 K; and a = 10.314(3), b = 9.663(2), c = 5.768(2) A, β = 91.23(3), Z = 4, space group Pn for the ferroelectric phase at 173 K. An external field of 15 KV/cm was applied to the crystal at the transition temperature before the low temperature measurements. The atomic parameters of the two structures were determined by full‐matrix least‐squares methods. The final agreement indices are R(F2) = 0.038, Rw(F2) = 0.049 on 748 reflections for the paraelectric structure and R(F2) = 0.035, Rw(F2) = 0.044 on 1636 reflections for the ferroelectric structure. The results resolve a controversy concerning the ordered hydrogenic state in the ferroelectric phase. Local charge neutrality is found for each molecular unit NaD...

Single crystal neutron diffraction studies are reported for cubic dinitrogen tetroxide (space group Im3; Z = 6). The crystals were grown from NO2 vapor in situ on the diffractometer by precise cryostatic control. The lattice parameter, measured at seven temperatures, increases from 7.6937(6) A at 20 K to 7.7925(6) A at 140 K. The nuclear positional and thermal parameters were refined using diffraction data (sin ϑ/λ⩽0.79 A−1) measured at 20, 60, and 100 K. Final fit indices R(F2) are 0.028, 0.034, 0.037, respectively. The observed N–N bond length and O–N–O angle are invariant between 20 and 100 K at values 1.7562(±4) A and 134.46(±6)° with individual e.s.d.’s of 0.001 A and 0.1°. The observed N–O bond length increases linearly from 1.1855(9) A at 100 K to 1.1893(5) A at 20 K; the extrapolated zero‐point value is 1.191 A. Ab initio self‐consistent field calculations using a two‐configuration wave function which allows partial occupation of the σ* MO (antibonding with respect to the two nitrogens) yields a r...

The preparation and crystal structure of (n‐C4H9)3S+F—·20H2O is reported. This hydrate is isostructural with the chlorine gas hydrate, 6Cl2·46H2O, having a pseudo body‐centered arrangement of H40O20 pentagonal dodecahedra in a cubic unit cell of approximately 12 A edge. The cations occupy large voids formed by the tetrakaidecahedra in the structure and are statistically disordered. The water structure is distorted as compared with the idealized polyhedral framework and there is evidence that the pentagonal dodecahedra may be occupied by a water molecule or a fluoride ion.

The crystal structure of isopropylamine octahydrate, 10(CH3)2CHNH2·80H2O, mp − 4°C, has been determined from three‐dimensional Weissenberg film data obtained at − 160°C with CuKα radiation. The crystals are hexagonal, P63 / mmc, with a = 12.30 A, c = 24.85 A. The structure was determined from the Patterson function and refined anisotropically to an R of 0.09 for 1041 observed reflections. The water structure is a clathrate‐type hydrogen‐bonded framework, which can be related to that of the cubic gas hydrates. It consists of layers of face‐sharing 14‐hedra (42 × 58 × 64), separated by pentagonal dodecahedra (512) and 16‐hedra (512 × 64). The amine molecules occupy positions with sixfold orientational disorder in the six 14 hedra and four 16 hedra per unit cell. They are hydrogen bonded to the water structure, singly within the 16‐hedra and doubly within the 14‐hedra. Because of the distortions caused by the inclusion of the amines in the 14‐hedra, there are additional voids in the arrangement of the 12‐, 1...

The compound (n‐C4H9)4N·C6H5COO·39½H2O forms tetragonal crystals with four molecules in the unit cell. The water structure is a hydrogen‐bonded clathrate framework, in the cavities of which are located the tetra alkyl ammonium cations. The oxygen atoms of the benzoate anions are hydrogen‐bonded to the water framework and form part of the polyhedral structure. This structure contains 10 pentagonal dodecahedra, 16 tetrakaidecahedra, and four pentakaidecahedra per unit cell. The 20 larger polyhedra are occupied by the 16 alkyl and four benzyl groups with a statistical disorder over two sets of equivalent cation and anion positions. There is evidence of additional hydrogen‐bonded water inside some of the dodecahedra which are distorted due to the presence of the ions.The clathrate framework is iso‐structural with that of other salts in this series, which have a very similar tetragonal lattice but differ in containing five tetra n‐butyl ammonium salt molecules per unit cell.

The structure of the tetrahydrofuran/hydrogen sulfide double hydrate has been determined from three‐dimensional single‐crystal data. The analysis confirmed the clathrate host lattice characteristic of 17‐A cubic (Type II) gas hydrates. The hexakaidecahedral voids enclose tetrahydrofuran molecules which appear to undergo free rotation. Statistically, 46% of the pentagonal dodecahedra are occupied by hydrogen sulfide molecules.

The crystallographic data for nine alkylamine hydrates are reported. The hydrates of C2H5NH2 and (CH3)2NH are isostructural with the 12 A cubic gas hydrates and have unit cells with symmetries Pm3n and Pm3, and dimensions a=12.17 and 12.55 A, respectively. Those of (CH3)3N and n‐C3H7NH2 have symmetry P6/mmm and unit cell dimensions a=12.41 A, c=12.50 A and a=12.20 A, c=12.38 A, respectively, while that of iso‐C3H7NH2 has symmetry P63/mmc and cell dimensions a=12.42 A, c=25.22 A. These hexagonal hydrates are related in their water structure to (iso‐C5H11)4N+F−·38H2O. n‐C3H7NH2 forms a second hydrate with monoclinic symmetry P21/n and unit cell dimensions a=12.58 A, b=21.20 A, c=17.47 A, β=89.3°; (C2H5)2NH forms two hydrates, one of orthorhombic symmetry Pbcn and unit cell dimensions a=13.44 A, b=11.77 A, c=27.91 A, and one of monoclinic symmetry P21/c and cell dimensions a=13.86 A, b=8.44 A, c=10.93 A, β=97.5°; (CH3)3CNH2 forms a cubic hydrate with a unit cell of symmetry I43d and dimensions a=18.81 A. The total mass contents of the unit cells, calculated from the cell dimensions and experimental densities, are used to derive the probable stoichiometric formulas.

The crystal data and preparation are discussed for 22 new peralkylated ammonium, phosphonium, and sulfonium salt hydrate crystals. Although these structures have not been determined in detail, it is possible to classify them according to the host‐lattice type and to draw conclusions by analogy with known structures concerning the order and disorder in the distribution of the cations and anions with respect to the water lattice.

The structure of (n‐C4H9)4N+F—·32.8 H2O is tetragonal, of space group P42/m with the unit‐cell dimensions a=23.52 A and c=12.30 A. The clathrate host structure is similar to that of the (n−C4H9)4N+C6H5−COO−·39.5 H2O and consists of a tetragonal pseudo body‐centered arrangement of groups of five face‐sharing pentagonal dodecahedra interlinked by tetrakaidecahedra and pentakaidecahedra. Whereas in the benzoate there are four salt molecules per unit cell, in the fluoride there are five. This difference in the number of guests accommodated in essentially the same host structure is possible because the four tetrakaidecahedra occupied by the benzoate groups are available for the four alkyl groups of the additional cation. In the fluoride hydrate, four of the cations have the central N+ atom at the fourfold positions (j) and that of the fifth is disordered over the twofold position (f). Thus the structure has lower symmetry than the benzoate hydrate, which is P42/mnm by reason of the disorder of the four cations over eightfold positions.The fluoride ions replace water molecules in the host lattice, with F—···O distances of 2.80 to 2.87 A forming an anionic host lattice. As in the other clathrate hydrate structures of this type, some of the pentagonal dodecahedra which are distorted by the presence of the cations are occupied by a guest species presumed to be additional water molecules.

The crystal structure of 16(CH3)3CNH2·156H2O has been determined from three‐dimensional x‐ray‐diffraction data obtained at −30°C. The crystals are cubic, space group I43d, with cell dimensions a=18.81±0.02 A. The host framework of hydrogen‐bonded water molecules consists of face‐sharing heptakaidecahedra which have three square, nine pentagonal, two hexagonal and three heptagonal faces. The square and pentagonal faces also form octahedra which complete the space‐filling arrangement. The amine molecules occupy the larger polyhedra as nonbonded guests undergoing marked oscillatory motion.

A detailed single‐crystal structure analysis is reported for ethylene oxide hydrate. This confirms the polyhedral host lattice formed by 46 hydrogen‐bonded water molecules in a cubic unit cell of 12.03 A with space‐group symmetry Pm3n. Disordered ethylene oxide molecules occupy the six equivalent tetrakaidecahedral cavities, and their electron‐density distribution suggests that they are hindered axial rotors. Additional guest molecules, either ethylene oxide, oxygen, or nitrogen molecules occupy the two dodecahedral cavities with high disorder and low statistical weight. The compound is therefore nonstoichiometric having the limiting formula 2M·6C2H4O·46H2O, in which the percentage of M is variable. If M is assumed to be entirely ethylene oxide, as is likely from the method of preparation, the composition of the crystals obtained from an equilibrated aqueous solution of 8 mole % ethylene oxide at 9°C is 6.4C2H4O·46H2O.

The crystal structure of tetramethylammonium hydroxide pentahydrate has been determined at 25°C by an analysis of the three‐dimensional x‐ray‐diffraction data. The unit cell is orthorhombic with a=12.57, b=10.96, c=7.91 A and contains four formula units. The OH− ions and H2O molecules form a hydrogen‐bonded framework based on the space‐filling arrangement of truncated octahedra. Equivalent (CH3)4N+ ions occupy the four available polyhedral cages in the unit cell and distort the cubic symmetry of the idealized oxygen lattice formed from undistorted face‐sharing truncated octahedra. Three carbon atoms of each cation are disordered giving rise to a circular distribution of electron density about the fourth N–C bond axis, which suggests that the cations are behaving as slightly hindered axial rotors. In the framework structure, the number of hydrogen‐bonded edges equals the number of available protons, with ⅓ and ⅔ of the oxygen atoms forming 3 and 4 bonds, respectively. The framework of this hydrate resembles closely that found in the acid hydrate HPF6·6H2O. Although the clathration of the cationic guests is similar in principle to that in the tetra‐n‐butyl and tetraisoamyl ammonium salt hydrates, the structural geometry of the host lattice is quite different since it is derived from the truncated octahedron, instead of the pentagonal dodecahedron.

The temperature scale used in the analysis of neutron diffraction study of cubic ZnS1, is corrected. The revised temperature scale2 is used to re‐examine the thermal parameters. (AIP)