Volume 210, Issue 10

Disordering in SiC is analyzed both theoretically and experimentally. Classification of the stacking faults into (i) intrinsic, (ii) twin-like and (iii) extrinsic faults is proposed. This classification correlates well with distinct diffraction effects, characteristic for specific faults. Based on proposed classification, the disordering in SiC β -powders obtained by SHS method (self-propagating high-temperature synthesis) is analysed both qualitatively and quantitatively. It is shown that in the β -powders a single cubic domain has an average size of approx. 55 Si–C double layers. Those domains separated by intrinsic faults (≈80%) form several hundred layers large blocks which are separated from each other by twin-like (≈5%) and/or extrinsic faults (≈15% of total number of stacking faults).

Slawsonite (SrAl 2 Si 2 O 8 ) from Sarusaka, Kochi Prefecture, Japan, is triclinic, space group P [unk], with a = 0.6145(1) nm, b = 0.8987(2) nm, c = 0.7456(3) nm, α = 90.01(3)°, β = 90.34(3)° and γ = 89.98(3)°, Z = 4 at T = 298 K. The cell dimensions are similar to the previous assignment to the monoclinic space group P 2 1 / a . The average structure was refined to R = 0.049 from 2695 reflections. A model is proposed for the real structure taking into account about 200 superstructure reflections. Thermal analysis revealed a phase transition to P 2 l / a at 593 K which is considered a new type of transition for the paracelsian-slawsonite group.

The structure analyses of the quartz-type form of GaPO 4 crystals were carried out by using X-ray diffraction intensities at six points of temperatures from 293 K to 747 K. Temperature dependence of the thermal and positional parameters of atoms was examined by applying the conventional harmonic structure-factor expression and also a generalized structure factor expression. Thermal vibrations of oxygen atoms are highly anisotropic, being contributed by dominant librational motions of Ga–O–P planes around the Ga–P lines like those of the corresponding moiety in quartz or berlinite. Both the atomic positions and the directions of the principal axes of the thermal ellipsoids are quite reluctant to change with varying temperature unlike those of quartz or berlinite. According to the anharmonic refinements, the Ga–O and P–O bond distances are about 1.84 Å and 1.54 Å, respectively, which are longer than the values obtained in the harmonic refinements. In GaPO 4 , the Ga–O and P–O bonds are rigid, but O–Ga–O and O–P–O angles are rather flexible, and the structure with the smaller unit-cell than that of the berlinite form of AlPO 4 is maintained by bending the Ga–O–P bonds to such a small angle as 133°. It is indicated that, if GaPO 4 took the high symmetry configuration of the high temperature form of berlinite, the tetrahedral angles would be too strongly distorted.

Samarium sodium bis(nitrosylpentacyanoferrate-(II)) heptahydrate/(I) crystallizes in space group Pmma : a = 25.032(3) Å, b = 7.824(1) Å, c = 6.277(1) Å; V = 1229.4(3) Å 3 , Z = 2, D x = 1.976 g cm −3 , Mo K α = 0.71069 Å, μ = 36.10 cm −1 , F (000) = 710, T = 293 K; conventional R = 0.020; R w = 0.033 for 1469 observed reflections. Gadolinium sodium bis(nitrosylpentacyanoferrate-(II))heptahydrate/(II) crystallizes in space group Pmma : a = 24.963(4) Å, b = 7.807(6) Å, c = 6.264(3) Å; V = 1224.7(11) Å 3 , Z = 2, D x = 2.002 gcm −3 , Mo K α = 0.71069 Å, μ = 39.39 cm −1 , F (000) = 714, T = 293 K, conventional R = 0.032; R w = 0.043 for 1288 observed reflections. In both isomorphous structures the iron atoms are coordinated to five cyanide ligands and one nitrosyl group, while the sodium atoms are coordinated to four cyanide groups and two water molecules. Both centres have distorted octahedral symmetries. The coordination sphere of the second cation, samarium and gadolinium, respectively, consists of four cyanide groups and five water molecules. Cyanide bridges connect the iron, sodium, and the samarium/gadolinium polyhedrons forming sinusoidal layers.

The three structures were solved by direct methods and refined by full-matrix least-squares procedure. 2-phenyl-1 H -benz[ f ]isoindole-1,3(2 H )-dione, (compound 1 ): orthorhombic, space group Pcab , a = 7.618(1) Å, b = 11.717(2) Å, c = 28.540(4) Å, V = 2547.4(7) Å 3 , Z = 8 and d = 1.425 Mg m −3 , R = 0.038 ( R w = 0.038) for 190 parameters and 820 observations with I > 2.5 σ (I). 2-phenyl-1 H -benz[ e ]isoindole-1,3(2 H )-dione (compound 2 ): orthorhombic, space group Pc 2 1 b , a = 6.7042(9) Å, b = 7.4589(9) Å, c = 26.441(7) Å, V = 1322.4(4) Å 3 , Z = 4 and d = 1.373 Mg m −3 , R = 0.037 ( Rw = 0.032) for 190 parameters and 1186 observations with I > 3σ(I). 2-phenyl-1 H -benz[ de ]isoquinoline-1,3(2 H )-dione (compound 3 ): monoclinic, space group C 2/ c , a = 13.501(3) Å, b = 13.212(4) Å, c = 8.305(2) Å, β = 116.24(2)°, V = 1329(9) Å 3 , Z = 4, and d = 1.366 Mg m −3 , R = 0.038 ( Rw = 0.033) for 71 parameters and 754 observations with I > 3σ(I). The plane of the N -phenyl substituent has an axis which lies in the plane of the naphthalimide part and passes by the carbon atom bound to the nitrogen atom and by the carbon in para position. It makes a dihedral angle with the plane of the naphthalimide moiety of 59.2°, 46.5° and 69.4° for the compounds 1 , 2 and 3 respectively. This difference in geometry between the three molecules brings new insights into their spectroscopic properties.

Single crystals of FeCl 2 (pyz) 2 were prepared for the first time by sol-gel technique using pyrazine in tetramethoxysilane (TMOS) as the gel-forming reagent. The red polymeric Fe(II) complex crystallizes in the orthorhombic space group Ccca with lattice parameters a = 10.236(2) Å, b = 10.599(2) Å, c = 10.291(2) Å and Z = 4 formula units. The structure consists of infinite Fe(pyz) 2 layers parallel (010) with a square planar Fe–N 4 coordination completed to a nearly undistorted square bipyramide by the two chloro ligands.

Bis(zinc-dibutyldithiopercarbamate)/I crystallizes in two polymorphic forms herein named as I α and I β . I α : (C 18 H 36 N 2 O 2 S 4 Zn) 2 , space group P 2 1 / n (Nr. 14), a = 18.402(4) Å, b = 13.788(5) Å, c = 20.449(3) Å, β = 91.55(1)°, V = 5186.6 Å 3 , Z = 4; D x = 1.295 g cm −3 , Mo K α ( λ = 0.71069 Å), μ = 12.93 cm −1 , F (000) = 2144, T = 293 K, conventional R = 0.081, R w = 0.112 for 4121 observed reflections. I β : (C 18 H 36 N 2 O 2 S 4 Zn) 2 , space group P 2 1 / c (Nr. 14), a = 9.742(2) Å, b = 18.569(3) Å, c = 15.083(4) Å, β = 108.62(2)°; V = 2585.8 Å 3 , Z =2; D x = 1.299 g cm −3 , Mo K α ( λ = 0.71069 Å), μ = 12.97 cm −1 , F (000) = 1072, T = 293 K, conventional R = 0.134, R w = 0.141 for 2217 observed reflections. In both crystalline forms the molecules of I build up dimers consisting of two C 18 H 36 N 2 O 2 S 4 Zn units and in which two zinc atoms are linked by two oxygen bridges forming a central four membered ring. All molecules have same configuration but there are remarkable conformational differences.