Band 216, Heft 12

The temperature dependence of lattice parameters a in the quasiperiodic plane and c in the periodic direction of decagonal Al 70.7 Co 13.3 Ni 16.0 was probed using X-ray powder diffraction in the temperature range 15–300 K. Both parameters were fitted by means of positions of 22 Bragg reflections for each temperature. Temperature dependences were modelled best by second order polynomials leading to linear thermal coefficients α ( T ) = 8.1(33) · 10 –7 K –1 + 3.9(2)· 10 –8 K –2 T in the quasiperiodic plane and γ ( T ) = 1.7(6) · 10 –6 K –1 + 3.8(3) · 10 –8 K –2 T in the periodic direction, respectively. Thus we found the anisotropy ratio γ ( T )/ α ( T ) to decrease with increasing temperature from 1.10 (at 15 K) to 1.19 (at 300 K). Besides pecularities around 150 K indicating an intermediate phase formed by superordering, we observed deviations from the general smooth course between 15K and 50K for both lattice parameters.

At high temperatures yellow strontium chromate aluminate sodalite Sr 8 [Al 12 O 24 ](CrO 4 ) 2 has cubic symmetry with orientational disorder of the CrO 4 2- -ions within the sodalite cages. The existence of two phase transitions at 299 K and 289 K, which result in superstructures of tetragonal and orthorhombic symmetry, respectively, is well known. The structure of the orthorhombic low-temperature phase has been solved recently. In this work we discuss the crystal structure of the intermediate phase and its determination from neutron and x-ray powder diffraction data. The structure of this phase shows only very small distortions of the framework of AlO 4 -tetrahedra. The CrO 4 -tetrahedra within the sodalite cages are partially ordered. The observed distribution of their orientations can be described as a combination of those of the low- and the high-temperature phase. 27 Al-MAS-NMR spectra reveal the dynamic nature of the structure.

X-ray structure analyses of orthorhombic betaine fumarate and monoclinic betaine maleate yielded space group Pnma , a 1 =26.510(5) Å, a 2 =6.684(1)Å, a 3 =6.376(1)Å, Z =4, ρ calc =1.371g cm -3 , ρ obs =1.370 g cm -3 and, respectively, space group P 2 1 / n , a 1 =6.132(1)Å, a 2 =10.823(2)Å, a 3 =17.246(3)Å, α 2 =92.87(3)°, Z =4, ρ calc =1.355 g cm -3 , ρ obs =1.351 g cm -3 . In both compounds the hydrogen betaine cations are joined to the corresponding anions by strong H-bonds with O···O distances of about 2.48Å. Large single crystals of optical quality of betaine maleate have been grown from aqueous solutions. Further, we determined their coefficients of thermal expansion and their elastic and thermoelastic constants. In comparison to the pronounced anisotropy of the mechanical properties of betaine fumarate, the elastic constants of betaine, maleate appear only slightly anisotropic. Between 80 K and 305 K no phase transision could be detected in betaine maleate. However, softening of certain acoustic modes at temperatures below about 160 K might be a hint at structural instabilities at even lower temperatures.

A new organic semiconductor with trinitroresor-cinol as the anion, (TMTTF) 2 (C 6 H 2 N 3 O 8 ) ( 1 ) (TMTTF: tetramethyltetrathiafulvalene), has been synthesized and its crystal structure has been investigated at room and low temperatures (295 and 110 K). The crystal structure of 1 is formed by one-dimensional stacks of cation-radicals (TMTTF) +1/2 separated by trinitroresorcinol anions (C 6 H 2 N 3 O 8 ) – . This novel salt reveals semiconducting properties. Tight-binding band structure calculations for 1 have been carried out in order to understand the charge distribution among the different donors.

The title compound was synthesized by reaction of N-(azidomethyl)thiourea or N-(tosylmethyl)thiourea with α -phenylsulfonylacetophenone in the presence of sodium hydride followed by p -toluenesulfonic acid treatment of the obtained N-[3-oxo-3-phenyl-2-(phenylsulfonyl)propyl]thiourea. The molecular and crystal structure of 6-phenyl-5-phenylsulfonyl-1,2,3,4-tetrahydropyrimidine-2-thione (C 14 H 13 N 2 S 2 O 2 ; space group P2 1 / a ; Z =4; a =17.396(1) Å, b =5.887(1) Å, c =15.665(2) Å, β =104.89(1) o ) have been determined and refined from neutron (the neutron diffraction was very effective for describing of this system due to using of partial hydrogen-deuterium substitution) powder diffraction data using grid search and a Rietveld procedures. The crystal structure is formed by centrosymmetric hydrogen-bonded dimers along a axis.

The crystal structures of twelve different DL-malates have been determined and refined from single-crystal X-ray diffraction data. In addition, powder diffrac-tion data were used for the refinement of the lattice pa-rameters. The title compounds are the neutral DL-malates Li 2 (C 4 H 4 O 5 )·2H 2 O (space group P 2 1 / c ), Mn(C 4 H 4 O 5 )·3H 2 O ( Pbca ), Cd(C 4 H 4 O 5 )·3H 2 O ( P 2 1 / n ), Sr 2 (C 4 H 4 O 5 ) 2 ·5H 2 O ( P 1̅) and Ba(C 4 H 4 O 5 ). 2H 2 O ( P 1̅) as well as the acid DL-malates RbH(C 4 H 4 O 5 ) ( Fdd 2), CsH(C 4 H 4 O 5 )·H 2 O ( P 2 1 / n ), MgH 2 (C 4 H 4 O 5 ) 2 ·4H 2 O ( C 2/ c ), CaH 2 (C 4 H 4 O 5 ) 2 ·2H 2 O ( C 2/ c ), ZnH 2 (C 4 H 5 O 5 ) 2 ·4H 2 O ( C 2/ c ), LiH 3 (C 4 H 4 O 5 ) 2 ( P 1̅), CsH 3 (C 4 H 4 O 5 ) 2 ( P 1̅). A comparison of DL-malate structures and a scheme of structural characterization according to cation polyhedra connection is proposed.

A simple procedure for deriving absorption corrections for crystal-environment diffractometer attachments of radial symmetry, like high-pressure cells, cryostats, furnaces or capillaries, from the direction cosines of the primary and diffracted beams is presented. This method is applicable irrespective of the diffractometer type, equally for point and area detectors.