Volume 135, Issue 3-4

β eucryptite, Li 2 O · Al 2 O 3 · 2SiO 2 , has a high-quartz-like structure. It crystallizes in the space group P 6 2 22. X-ray diffraction photographs of single crystals show, besides the main reflections of a high-quartz-like subcell, superstructure reflections which lead to doubling of the lattice constants of the subcell. The intensities of the main reflections were used to investigate the average structure and its likeness to the ideal high-quartz structure, which was used as the starting model for the structure refinement. The Li atoms are located in the main channels parallel to the c axis. They are coordinated by four oxygen atoms. The “thermal” vibrational ellipsoid of the oxygen atoms shows an unusually large main axis of 0.2 Å, due to the superstructure (cf. part II). The mean (Si, Al) –O distance is 1.68 Å, the final unweighted R value is 0.050.

The superstructure of β eucryptite shows an alternating sequence of Si and Al layers. For a Si-Al ratio of 1:1 only in this arrangement each AlO 4 or SiO 4 tetrahedron can be surrounded by four SiO 4 or AlO 4 tetrahedra, respectively. The Li atoms also have an ordered distribution. The following mean values of bond distances were obtained: Si–O = 1.606 Å, Al–O = 1.733 Å, Li–O = 2.02 Å. The shortest O–O distance of SiO 4 tetrahedra is 2.48 Å. For refinements with anisotropic temperature factors the final R values of the superstructure reflections and of all reflections were 0.088 and 0.057, respectively.

Structural-geometrical schemes for the creation of structural series for cadmium iodide polytypes have been worked out based on layer-transposition mechanism. The existence of all the cadmium iodide polytypic series have been accounted for. The occurrence of polytypic structural series has remained inexplicable so far based on the layer transposition mechanism; the present study therefore lends direct support to J agodzinski 's layer-transposition mechanism.

The nuclear magnetic resonances of 23 Na and 27 Al in nepheline are characterized by the usual absence of satellite lines of the quadrupole splitting. In a nepheline from Ontario, Canada, showing broad inner satellites of 27 Al the quadrupole coupling constant of 23 Na has been estimated to lie between 1.5 and 2.0 MHz, the coupling constant of 27 Al is probably less than 1 MHz. The results prove that a high degree of cation disorder must exist in nepheline. In addition, it is very likely that domain disorder may play a role.

The structure of an interstratified mineral which has 38 Å x-ray superreflections was analysed. X-ray basal reflections at d = 38, 18.3, 11.6, 9.00, 4.91, 3.20, 1.94 Å in natural specimen change to 40, 19.1, 12.2, 9.32, 5.22, 4.61, 3.31, 1.92 Å by treatment with ethylene glycol and 9.9, 4.93, 3.26, 1.95 Å by heat treatment at 400°C. Differential-thermal-analysis curve shows several endothermic peaks at 150, 200, 580 and 980°C. These data suggest that this specimen is an interstratified mineral of illite and montmorillonite. In order to determine this structure, a correlation method was applied by using K akinoki and K omura 's equation in the cases of both Reichweite g = 1 and g = 2. As the result, it has been disclosed that this super-reflection is due to a longitudinal disordered structure with Reichweite g = 2. The probability parameters defining the structure can be shown as: W A (illite layer existing probability) = 0.7, W B (montmorillonite layer existing probability) = 0.3; pair layer existing probabilities W AA = 0.4, W AB = 0.3, W BA = 0.3, W BB = 0.0; transition probability matrix [unk]

Methods are outlined for various types of calculations for the four-circle diffractometer which include: (1)calculation of the Eulerian setting angles and (2), determination of the crystal-specimen orientation.

The crystal structure of the mineral analcime, NaAlSi 2 O 6 · H 2 O, known from x-ray analysis to approximate closely to the cubic space-group symmetry Ia 3 d , has been examined by neutron diffraction. Intensity data from a single crystal were collected for one octant so as to be representative of cubic and some lower symmetries. In general, the systematic absences were consistent with the space group Ia 3 d ; within experimental error, the six reflections equivalent for Laue group m 3 m were equal in intensity. From Fourier difference syntheses and least-squares refinements, it is concluded that the neutron data, like the x-ray data, are consistent with an averaged Ia 3 d structure. Full-matrix least-squares refinement with the constraints required by the Ia 3 d space group gave a final R value of 0.044 over 194 independent reflections. Hydrogen atoms are distributed in 32 e and 96 h positions and are not engaged in hydrogen bonds. Apparent values for the H–O–H angle probably depend on the averaging of arrangements for the water molecules; interpretations are suggested in terms of static and dynamic models.

The crystal and molecular structures of ammonium sulfamate, NH 4 SO 3 NH 2 , have been determined using the intensities of 560 independent reflections measured from integrated Weissenberg photographs obtained with Cu Kα radiation. The compound crystallizes in the orthorhombic system with space group Pbca . The unit-cell dimensions are: a = 7.443 ± 0.001 Å, b = 7.739 ± 0.001 Å, and c = 14.281 ± 0.002 Å; ϱ obs = 1.81 g cm −3 and ϱ calc = 1.84 g cm −3 for Z = 8. The sulfamate ion is essentially tetrahedral, with all angles being 109 ± 4°, and has bond lengths of 1.44 Å for S–O and 1.64 Å for S–N. Anisotropic refinement of three-dimensional data by least squares led to a final unweighted R factor of 9.7%. The S–N bond length is shorter than that found in sulfamic acid and is ascribed to non-zwitterionic character. Extensive hydrogen bonding is proposed but the hydrogen atoms were not located in the structure analysis.

The crystal structure of 1-acetyl 2-ethoxynaphthalene, C 14 H 14 O 2 , has been determined using three-dimensional x-ray diffraction data and refined by the method of least-squares using anisotropic temperature factors for individual atoms, leading to an R value of 0.138 for 590 observed reflections. The molecules, in the triclinic unit cell, are held together by only weak van der Waals forces with intermolecular contacts ranging from 3.56 Å to 4.00 Å between atoms of neighbouring molecules. The bond lengths and angles in the molecule are normal. The O = C–CH 3 group is twisted out of the plane of atoms comprising the naphthalene group by 63° 45′.

The crystal structure of the rubidium salt of homophthalic acid (C 9 H 8 O 4 ), with the empirical chemical formula Rb(C 9 H 7,5 O 4 ) 2 , has been determined using three-dimensional x-ray diffraction data, refined by the method of least squares and anisotropic temperature factors for each individual atom, to an R value of 0.099. The unusual point of interest is that the rubidium atom occupies a special position on a twofold axis (0 y 1/4) in a monoclinic unit cell, a = 32.81 5 Å, b = 5.47 9 Å, c = 9.95 6 Å, β = 95° 54′, Z = 8, space group C 2/ c . There is fourfold coordination around the rubidium with rubidium-oxygen distances ranging from 2.86 Å to 2.88 Å. In the crystal, the molecules are held together by metal-oxygen ionic linkages, a short hydrogen bond of 2.61 Å between oxygen atoms belonging to carboxyl groups of adjacent homophthalic acid molecules, an ultrashort symmetrical hydrogen bond of 2.45 Å between two centrosymmetrically related oxygen atoms with the hydrogen atom midway and occupying a special position of centre of symmetry and weak van der Waals contacts. Both the end carboxyl groups in the homophthalic acid molecule are rotated out of the plane of the central aromatic ring by 12° 11′ and 98° 29′ respectively.

Large single crystals of Al(JO 3 ) 3 · 2HJO 3 · 6H 2 O, space group P 6 3 , have been grown from acid aqueous solutions. The piezoelectric, elastic, thermoelastic, and optical properties are measured. This new material exhibits a longitudinal piezoelectric effect parallel to the sixfold axis about ten times stronger than α quartz.

The crystal structure of p -dimethylamino-phenylene-diphenylenephosphin has been determined by Patterson synthesis and refined by full-matrix least-squares methods. The structure is monoclinic, space group P 2 1 / n , with lattice constants a = 18.302, b = 8.961, c = 10.542 Å, β = 95.13°. Three-dimensional intensity data were collected with a four-circle diffractometer. The reliability index, including the twenty hydrogen atoms, is 4.6%.

A refined set of atomic coordinates and temperature parameters have been obtained for stibnite, Sb 2 S 3 . This structure contains parallel (Sb 4 S 6 ) n chains, which are linked to form crumpled sheets (two per unit cell). The quinvalent Sb has fivefold coordination in a square pyramid, where the Sb is slightly displaced out of the base center. The trivalent Sb has threefold coordination in a trigonal pyramid, where the Sb occupies the vertex. Two trivalent S have threefold coordination in a trigonal pyramid, where the S occupies the vertex. The other divalent S has twofold coordination. The physical properties are related to the crystal structure.