Band 189, Heft 3-4

Crystals of the title compound, C 17 H 18 N 2 O, are monoclinic with a = 11.231(5) Å, b = 15.757(10) Å, c = 8.729(6) Å and β = 111.97(2)°, space group P 2 1 / a , Z = 4. Atomic positions have been determined by direct methods from single crystal X-ray diffraction data and refined by least squares to R = 5.0% for 793 independent reflexions. The structure contains a non-planar 4,5 dihydroisoxazole heterocycle, to which an amino group and two phenyl rings are bound.

Single crystals of (C 2 H 2 N 2 S 3 ) 2 Bi(SCN) 3 have been prepared from solution and its structure has been determined. (C 2 H 2 N 2 S 3 ) 2 -Bi(SCN) 3 is monoclinic, space grouip C 2/ c , a = 6.730(4), b = 13.285(4), c = 20.679(4) Å, β = 96.92(5)°, Z = 4. Four sites of the strongly distorted tetragonal antiprism forming the coordination polyhedron of the Bi atom are occupied by S and N atoms of two isoperthiocyanic acid molecules (isoperthiocyanic acid: 5-amino-3-thione-1,2,4-dithiazole). The C 2 N 2 S 3 disubstituted five membered ring units of the isoperthiocyanic acid molecules are planar. The other four sites of the coordination polyhedron are occupied by S and N atoms of thiocyanate ions. Two of them form bonds via S to the Bi atom. A third thiocyanate group acts as a bidentate ligand, connecting neighbouring Bi atoms. These ambidently bridging thiocyanate ions are disordered, thus leading to infinite chains made up of equal numbers of – Bi – S – C – N – Bi′ – and – Bi – N – C – S – Bi′ – units, running nearly parallel to the crystallographic a -axis. The Bi – S distances range form 2.814(3) to 2.919(2) Å, the Bi – N distances are 2.695(6) Å for the binding N atom of the isoperthiocyanic acid molecule and 2.66(2) Å for the N atom of the disordered bridging thiocyanate ion, respectively. A possible location of the Bi(III) lone pair is briefly discussed.

CsBaCr 3 F 12 is monoclinic (S.G.: C 2/ c ): a = 17.184(4) Å, b = 9.886(2) Å, c = 15.037(5) Å, β = 124.32(2)°, Z = 8. The structure was solved from single crystal data using 2218 independent reflections ( R = 0.053, R w = 0.042). The structure is built up from [Cr 3 F 12 ] layers of vertex-sharing octahedra separated by cesium and barium ions located in an ordered way. The topology of the layers is unique and illustrates a case of plane net predicted by O'Keeffe, yet unknown in nature but imaginated by arabic artists in the 18th century.

An X-ray diffraction analysis was performed on a single crystal of natural tetragonal natrolite (Marianberg, Bohemia), (Na 1.81 Ca 0.10 )-[(Al 1.92 Si 3.08 )O 10 ]·2.08H 2 O, tetragonal I [unk]2 d , a = 13.074(3) Å, c = 6.620(2) Å, Z = 4, V = 1131.5 Å 3 , D obs. = 2.272, D calc. = 2.230. Refinement of 860 independent reflections yielded R = 0.034. The average Si – O, Si(Al) – O, O(W) – O and Na – O distances are 1.6259, 1.6667, 2.9769 and 2.2103 Å, respectively. The alumosilicate framework of tetragonal natrolite is topologically the same as in the orthorhombic natrolite modification.

Tokkoite, K 2 Ca 4 [Si 7 O 18 (OH)](F,OH), a new mineral from Murun massif, South Yakutia, USSR, is triclinic with unit-cell dimensions a = 1.0438(3) nm, b = 1.2511(3) nm, c = 0.7112(2) nm, α = 89.92(2)°, β = 99.75(2)°, γ = 92.89(2)°, space group P [unk], Z = 2. The crystal structure has been determined by the Patterson method and difference Fourier maps followed by a least-squares refinement to an R factor of 0.032 for 906 ( I > 1.96 σ I ) reflections measured on an automatic single-crystal X-ray diffractometer. The structure consists of corrugated walls of calcium octahedra parallel to (100), between which bands of silicon – oxygen tetrahedra are situated. One of the non-bridging end anions is a OH group. K atoms are located within zig-zag channels formed by curved silicate bands. Tokkoite and tinaksite, K 2 Ca 2 NaTi [Si 7 O 18 (OH)]O, are isostructural. These two structures are related by the substitution 2Ca 2+ ⇌Ti 4+ + Na + and (F,OH) − ⇌ O 2− which occurs simultaneously in kationic and anionic parts of minerals. Common structural details of tokkoite, miserite and canasite are also considered.

A series expansion distribution function of the structure amplitude | F | has been used to calculate the generalised cumulative distribution function N n ( z ) for hypersymmetric crystals when there are n -fold repetitions of motifs at regular intervals ‘ d ’ along a straight line (both centrosymmetric and non-centrosymmetric motifs have been considered). The resultant change from the corresponding Wilson-type distribution is illustrated with the help of a hypothetical example, and the effects of expansion terms are discussed.

Crystals of N-benzyl-2,4,6-triphenyl pyridinium boron tetrafluoride C 30 H 24 BF 4 N belong to the monoclinic system, P 2 1 /C, with cell dimensions a = 9.633(2), b = 14.884(2), c = 17.166(2) and β = 93.5(2)°. The structure was solved by direct methods using the program SHELX. The refinement using block diagonal least squares led to R = 0.13. Further cycles of anisotropic refinement including the hydrogen atoms in their geometrically assigned positions improved the reliability factor to R = 0.07. Torsion angles were calculated and rings A, B, C, D and E showed to be planar within experimental errors.

Thermal dehydration of goethite ( α -FeOOH) at low temperature leads to complete transformation into a hematite-like phase before less than one half of the stoichiometric water content in goethite is expelled. The character of the remaining water has not bee explained as yet. The variations of band positions in the infrared spectra and the specific changes in relative integrated intensities of X-ray lines with the increase of dehydration temperature suggested that OH-groups replace oxygen anions in the hematite crystal lattice, while the electroneutrality is preserved by the cation vacancies. Comparison of integrated intensities observed with intensities calculated on this assumption fully confirms that the hematite-like phase is an iron deficient species with a general chemical formula α -Fe 2− x /3 -(OH) x O 3− x . The accurate measurements of lattice constants reveal that while the crystallographic c o -axis decreases steadily with progressing thermal dehydroxylation, the a o -axis reaches a minimum at the temperature at which the nonuniform X-ray line broadening disappears. The largest unit cell of hematite phase after the goethite/hematite transition and the smallest one after the disappearance of selected broadening of X-ray diffraction peaks represent two transitional phases with hematite structure, protohematite and hydrohematite, displaying their own structural and compositional characteristics. The smallest unit cell appearing when the crystalline phase still holds about three percent of structurally bound water suggests that the stoichiometric hematite is thermodynamically less stable than this intermediate state.

Within the framework of the coincident-site lattice (CSL) description of grain boundaries (GBs), the five macroscopic degrees of freedom (dof) are usually chosen to consist of a rotation axis and angle and the GB-plane normal. A different method is proposed for the characterization of these five independent parameters, by replacing the CSL misorientation by the GB-plane normals in the two halves of the bicrystal and by the twist component of the misorientation. The relevant expressions describing the transition from the one to the other are derived and illustrated. The new scheme has the advantage that (a) it readily allows one to visualize the unrelaxed atomic structure of the interface; (b) symmetrical GBs are easily identified; (c) the tilt and twist components of general GBs are readily apparent; and (d) the new scheme may be applied equally to GBs and to dissimilar-material (commensurate or incommensurate) interfaces. Within the new characterization scheme, the well-known fact that in cubic crystals with inversion symmetry, the symmetrical tilt GB on a given lattice plane may be considered as the most special of all twist boundaries, is easily recognized.

The crystal structure of the title compound (NiC 24 H 28 O 8 N 2 ) has been determined by X-ray diffraction methods in order to ascertain the positions of coordination of the nickel atom and the organic moiety. Crystals are triclinic, space group P [unk] with a = 8.309(1), b = 8.756(1), c = 10.600(1)Å, α = 99.21(1), β = 107.21(1), γ = 113.40(1)°, V = 641.3(2)Å 3 , Z = 1, D = 1.375 g·cm −3 , λ (Cu Kα ) = 1.5418 Å, μ = 14.77 cm −1 , F (000) = 278, T = 293°K. The final R was 0.062 for 1548 observed reflections. The structure is monomeric with slightly distorted octahedral coordination geometry. The configuration is trans . The coordination of the polyketide moieties is established by the two ketonic oxygens. The nickel is center of symmetry.

The surface morphology and the dislocation structure of MOCVD grown In 1− x Ga x As epitaxial layers ( x ≈ 0.5…0.73, tensile stress conditions) on (001) surfaces of InP substrates have been studied for layers of various thicknesses ( t = 0.6…4.5 μm). Surface corrugations due to dislocation slip parallel [1[unk]0] and due to fracture parallel [110] have been studied quantitatively and correlated to the internal dislocation structure. Tensile strain of the layer is released by nucleation of partial dislocations at the free surface and not at the layer/substrate interface. The model of Marée et al. is in good agreement with the observations. From simple crystallographic arguments it is concluded that partial dislocations with excess In-Ga atoms in the core can be generated more easily than dislocations with excess of As atoms.

The crystal and molecular structures of 1-(m-nitrophenyl)-2,2-dicarboethoxy-3-phenyl-pyrrolidin-5-one (I) and 1-(p-chlorophenyl)-2,2-dicarboethoxy-3-phenyl-pyrrolidin-5-one (II) have been determined by X-ray diffraction methods. (I) crystallizes in the monoclinic space group C 2/ c with cell dimensions a = 18.618(16) Å, b = 10.606(9) Å, c = 21.163 (18) Å and β = 96.59(1)°. (II) crystallizes in the space group P [unk] with a = 9.590(7) Å, b = 10.771(8) Å, c = 10.849(9) Å, α = 91.63(6)°, β = 94.80(6)°, and γ = 110.55(5)°. The structures were solved by direct methods and refined by least-square procedures to final R -values of 0.062 (I) and 0.059 (II) for 1985 (I) and 1868 (II) unique observed reflections with I ≥ 3 σ ( I ). In (I) one of the carboethoxygroups shows some disorder.

The crystal structures of three benzanilide derivatives, which are oligomers of fire resistant polymers, are reported. The compound (I) is monoclinic, P 2 1 c , with a = 12.430(2), b = 13.535(2), c = 7.948(2) Å, β = 108.18(3)°; compound (II) is orthorhombic, P 2 1 2 1 2 1 , with a = 25.236(2), b = 9.019(2), c = 5.639(1) Å, compound (III) is monoclinic, P 2 1 / a , with a = 23.622(3), b = 9.581(2), c = 10.373(2) Å, β = 99.08(3)°. The three structures have been solved by direct methods and refined to R = 0.042 for 1740, to R = 0.049 for 1200 and to R = 0.050 for 3811 observed reflections for compounds (I), (II) and (III) respectively. Any molecule consists of four nearly planar parts: the ring of the benzoic acid, the amido group, the benzene ring methylated or not and the carboxylic group. Their reciprocal orientations, different in the three derivatives, is mainly due to the steric hindrance. Strong hydrogen bonds form dimers in compound (I) and infinite chains in compounds (II) and (III). Energy calculations have been carried out in order to discuss the different packings and their influence on the molecules of investigated compounds.