R. K. McMullan

Polyhedral Clathrate Hydrates. IX. Structure of Ethylene Oxide Hydrate

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.

Polyhedral Clathrate Hydrates. X. Structure of the Double Hydrate of Tetrahydrofuran and Hydrogen Sulfide

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.

Hydrates of the Tetra n‐butyl and Tetra i‐amyl Quaternary Ammonium Salts

The compounds [(n−C4H9)4N+]nXn−·nyH2O have been prepared where X is F‐, Cl‐, Br‐, CH3CO2‐, CrO42‐, WO42‐, C2O42‐, HCO3‐, HPO42‐, and y is approximately 32. They form an isomorphous crystal series which is tetragonal with a=23.65±0.15 A, c=12.40±0.15 A.A similar series of the type [(i−C5H11)4N+]nXn−⋅ny′H2O has been prepared where X is F‐, Cl‐, CrO42‐, WO42‐, and y′ is approximately 40. They also form an isomorphous group which is orthorhombic with a=12.10±0.10 A, b=21.50±0.15 A, c=12.65±0.15 A.These compounds are believed to be of the clathrate type, similar in general character to the gas hydrates.

Polyhedral Clathrate Hydrates. V. Structure of the Tetra‐n‐butyl Ammonium Fluoride Hydrate

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...

Polyhedral Clathrate Hydrates. III. Structure of the Tetra n‐Butyl Ammonium Benzoate Hydrate

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.

Polyhedral Clathrate Hydrates. XI. Structure of Tetramethylammonium Hydroxide Pentahydrate

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 resemble...

Polyhedral Clathrate Hydrates. VI. Lattice Type and Ion Distribution in Some New Peralkyl Ammonium, Phosphonium, and Sulfonium Salt Hydrates

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.

Polyhedral Clathrate Hydrates. XIV. The Structure of (CH3)3CNH2·9¾H2O

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.

Polyhedral Clathrate Hydrates. XII. The Crystallographic Data on Hydrates of Ethylamine, Dimethylamine, Trimethylamine, n‐Propylamine (Two Forms), iso‐Propylamine, Diethylamine (Two Forms), and tert‐Butylamine

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. Th...

Polyhedral Clathrate Hydrates. IV. The Structure of the Tri n‐Butyl Sulfonium Fluoride Hydrate

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.