Volume 210, Issue 7

The ab-initio solution of the crystal structure of the zeolite material RUB-10 from X-ray powder diffraction data at 2 Å resolution is presented. Microcrystallinity and poor crystallinity are inherent properties of this material that could not be overcome by optimizing the synthesis conditions. RUB-10 is monoclinic with space group P 2 1 / a and a = 13.112(2) Å, b = 12.903(1) Å, c = 12.407(2) Å, β = 113.50(1)°, V = 1925 Å 3 , unit cell content: [Si 32 B 4 O 72 ] [N(CH 3 ) 4 ] 4 . The general connectivity pattern of the silicate framework which belongs to the clathrasil family, was determined by introducing the relatively rigid building unit [Si 5 ] in a Patterson search in the aristotype symmetry C 2/ m . With the help of framework models based on distance least-squares refinements, detailed information was obtained about the topology of the silicate framework, the Si/B ordering and the location of the template species. The structure of RUB-10 is completely new (structure type code RUT), and the two cage-like subunits found, [4 4 5 4 6 2 ] and [4 4 5 6 6 5 8 1 ], have not yet been encountered in other porous structure types.

The ANNNI model (Axial Next-Nearest-Neighbor Ising model), as developed for the explanation of polytypism in magnetic structures, was the first to introduce entropy contributions to free energies of magnetic polytypes. Phonon and other contributions to entropy have recently been included, in order to interpret some of the polytypes of SiC and ZnS as thermodynamically stable structures. It is shown in this paper that polytypism is strongly dependent on crystal size in these cases. Hence disorder has to be included into the discussion of equilibrium conditions. Phonon and vibrational entropy seem to play the predominant role in the ordering process during crystal growth. Consequently, kinetics is also an important factor in interpreting the distribution laws of polytypic structures. The existence of certain branches may be explained with the aid of size degeneracies and size instabilities as defined in this paper.

The crystal structure of the sodium manganese(III) fluoride compound, Na 5 Mn 3 F 14 , has been reinvestigated. The previous structure model, assuming the non-centrosymmetric space group symmetry Pna 2 1 , has been transformed to the centrosymmetric symmetry Pnam . Least squares refinements, based on new collected single crystal X-ray diffraction data, converged smoothly with the new structural model and yielded an R -value of 0.022. The general structural features described earlier, as the structural relations to the chiolite structure, still applies. However, the changed space group symmetry introduces new symmetry constraints to e.g. some of the coordination polyhedra in the structure.

We have measured single crystal X-ray diffraction data of InS at ambient pressure and under hydrostatic pressures up to 4.3 GPa. The redetermination of the crystal structure at ambient conditions shows no major deviations from previous results. Determination of lattice parameters at various pressures confirms an extraordinary large compressibility for the b -axis and a pressure-induced elongation for c . Crystal structure refinements at different pressures show the dominant changes of atomic parameters to be in y (In) and y (S). As a result of these variations the tilt of In-In dumbbells with respect to the c -axis is reduced from 23.2° (ambient conditions) to 16.1° (4.3 GPa), and two long In–S distances are shortened from 349.2(1) pm to 304.1(5) pm. The coordination of indium and sulfur atoms is changed from 4 + 2 towards 6.

The structure of Al 13− x (Co 1− y Ni y ) 4 , with x = 0.9 and y = 0.12, a new monoclinic approximant of the decagonal phase in the system Al–Co–Ni, was determined by means of single-crystal X-ray diffractometry: space group C 2/ m (No. 12), a = 17.071(2) Å, b = 4.0993(6) Å, c = 7.4910(9) Å, β = 116.17(1)°, V = 470.5(1) Å 3 , Pearson symbol mC34-1.8, D x = 3.96 Mg/m 3 Mo K α , F (000) = 530.6, M r = 140.5, μ = 7.97 mm −1 , Z = 2, wR = 0.034 and goodness of fit S = 1.15 for 963 reflections and 58 refined parameters. Typical interatomic distances are: d Al−Co,Ni = 2.323 Å–2.733 Å, d Al−Al = 2.688 Å–2.956 Å, d Co,Ni∓Co, Ni = 2.891 Å, respectively. Co atoms are coordinated by nine to eleven atoms, Al atoms are surrounded by ten, twelve or 13 neighbors. The relationships to the structurally related quasicrystal approximants with compositions Al 13 TM 4 (TM = Co, Fe, Os, Rh, Ru) as well as to the Al–Co–Ni(Cu) decagonal phases are discussed.

At room temperature bis(trimethylphenylammonium) tetrachlorozincate, C 18 H 28 Cl 4 Zn, crystallizes in the monoclinic space group, C 2/ c , a = 1555.4(2) pm, b = 955.6(2) pm, c = 3086.6(5) pm, β = 95.38(1)°, Z = 8. The asymmetric unit contains two independent cations and one tetrahedral [ZnCl 4 ] 2− anion. The atoms of one cation occupy fixed positions in the crystal structure, the other cation shows disorder of the methyl groups. The X-ray data indicate that this disorder is caused by a dynamic rotation of the (CH 3 ) 3 N group. IR and Raman data are given at room temperature as well as the results of DSC measurements in the range from 190 K to 370 K.

The structure of decagonal Al 65 Cu 20 Co 15 , which was determined by single crystal X-ray diffraction method (Steurer, Kuo, 1990a, b), has been re-examined. By eliminating the weak peaks in the electron density maps, which are likely only artifacts in the Fourier transformation, we propose an ideal model of decagonal Al 65 Cu 20 Co 15 . The structure is composed of two quasiperiodic layers stacked periodically along the unique tenfold axis. These layers can be characterized as two-color Penrose tiling and the 10 5 screw axis is achieved by consecutive stacking two layers with 36° rotation between them. Therefore the structure of decagonal Al 65 Cu 20 Co 15 is assumed to be associated with a color quasilattice.

Li 2 ZrN 2 and Li 2 HfN 2 were synthesized from Li 3 N and ZrN/HfN in welded niobium ampoules at about 1273 K. Neutron diffraction on Li 2 ZrN 2 was carried out in order to get reliable positional parameters for nitrogen and lithium. Li 2 ZrN 2 and Li 2 HfN 2 crystallize with the trigonal structure proposed so far: space group P [unk] m 1, Z = 1. Li 2 ZrN 2 : a = 3.285(1) Å, c = 5.461(2) Å (neutron); Li 2 HfN 2 : a = 3.246(2) Å, c = 5.427(3) Å (X-ray).

The crystal structure of the title compound, C 35 H 62 N 2 O 11 · 2H 2 O, has been determined at room temperature by X-ray diffraction. The colorless crystals are monoclinic, space group C 2, with unit cell dimensions a = 16.407(8) Å, b = 11.679(6) Å, c = 22.710(11) Å, β = 102.63(3)°, Z = 4, D c = 1.140, D m = 1.131 Mg m −3 . The structure was solved by direct methods and refined by full-matrix least-squares procedure to final R = 0.058 using 3351 reflections. The conformation of the oleandomycin molecule is influenced by the sp 2 -hybridization at the C8 carbon atom as well as by intra- and intermolecular hydrogen bonds. All oleandomycin-hydroxyl groups and both water molecules participate in the hydrogen-bonds formation.

The single crystal structure of TDAE was redetermined at different temperatures. Phase transitions are observed by warming the samples from low temperatures but never by cooling. Due to this special behavior it was possible to cool single crystals to 90 K. The data collected from such supercooled crystals resulted in a more precise and reliable structure refinement. Interesting structural details of the sterically overcrowded molecule are elucidated. The temperature dependence of the distortions of the nonplanar dimethylamino groups indicates dynamic behavior rather than static disorder.