Band 240, Heft 1-2

Large lath-shaped single crystals of SrAl 8 Rh 2 were grown during attempts to synthesize SrAl 4 Rh 2 in analogy to SrAl 4 Ir 2 . Single crystal experiments determined the structure to be isostructural to the CeAl 8 Fe 2 type crystallizing in the orthorhombic crystal system with space group Pbam ( a = 1269.74(4), b = 1475.43(5), c = 412.55(1) pm, w R 2 = 0.0398, 2088 F 2 values and 70 variables). SrAl 8 Rh 2 is the first reported compound in the ternary system Sr–Al–Rh. No mixing on any atomic position was observed. Attempts to synthesize SrAl 8 Rh 2 in bulk led to a multiphase mixture according to powder X-ray diffraction experiments. However, here also growth of large single crystals was possible. Subsequently, electrical resistivity measured on a single crystal of SrAl 8 Rh 2 revealed an onset of superconductivity around T c = 0.8 K. Finally, quantum-chemical calculations gave an insight into the chemical bonding and the charge distribution, showing that the compound consists of a [Al 8 Rh 2 ] δ – polyanion with the Sr δ + residing in the pentagonal cavities.

Plagioclase feldspars draw intensive research attention in planetary sciences because of their abundance in the Martian regolith. Crystal chemical studies on plagioclase feldspars would be of crucial importance for possible in situ resource utilization for future human settlement on Mars. This study focuses on the synthesis of representative plagioclase feldspars followed by simulation of mechanical weathering using ball milling. A series of (Ca 1- x Na x )(Al 2- x Si 2+ x )O 8 plagioclase feldspars is synthesized perfoming the solid-state method, where the endmembers are the anorthite (CaAl 2 Si 2 O 8 ) and albite (NaAlSi 3 O 8 ). The bulk chemical composition, particularly the Al/Si ratio, of each member is determined from energy-dispersive X-ray spectroscopy, which is supported by X-ray powder diffraction data Rietveld refinements. Selective plagioclase members ( x  = 0.0, 0.4 and 1.0) are mechanically weathered using high-energy ball milling, leading to significant changes of microstructural features such as average crystallite size and micro-strain. Total scattering data are collected using in-house X-ray facilities and analyzed by pair distribution function refinements. The vibrational modes of the samples are evaluated by Raman spectroscopy, complementing the local structural description.

Thermal expansion of the mineral soddyite, (UO 2 ) 2 SiO 4 (H 2 O) 2 , and structurally related synthetic compound Na 2 (UO 2 ) 2 SiO 4 F 2 ( NAUSIF ) has been studied by means of high-temperature single-crystal and powder X-ray diffraction. The mineral is orthorhombic, Fddd , while NAUSIF is tetragonal, I 4 1 / amd . The framework structures of both compounds are comprised of either neutral [(UO 2 ) 2 (SiO 4 )(H 2 O) 2 ] or negatively charged [(UO 2 ) 2 (SiO 4 )F 2 ] 2- chains of similar topology. In the structure of soddyite, the chains cross at the angle of 72°, while in NAUSIF of 90°. Upon increasing temperature, the acute inter-chain angles in soddyite increase due to hinge deformations, the overall symmetry approaching tetragonal. The mineral is stable below 325 ± 25 °С; between 325 and 640 °С, the decomposition products cannot be identified unambiguously and contain significant amount of amorphous phases; at higher temperatures, a mixture of U 3 O 8 polymorphs is formed. NAUSIF is stable until its melting point of 625 ± 25 °С. The thermal expansion of both compounds is strongly anisotropic; for NAUSIF , it is due to difference in bond strength in the uranium and sodium polyhedra. Anisotropic thermal expansion of soddyite is controlled by shear deformations of the structure upon the temperature rise.

Copper(I)seleonocyante, Cu[SeCN], is known as a hole-transport layer (THL) material and finds application in transistors and organic light-emitting diodes. Previous works also include a prediction of the crystal structure of Cu[SeCN] by density functional theory analysis. Presumably, as-synthesized Cu[SeCN] forms its α -modification and, if deposited as a layer, it forms its β -modification. However, these statements are based only on the qualitative comparison of the collected and predicted diffraction patterns. Here, we present the complete structural refinement of the crystal structure of α -Cu[SeCN] from powder X-ray diffraction data. α -Cu[SeCN] crystallizes in the α -Cu[SCN] type in the orthorhombic space group Pbca (№ 61) with lattice parameters a  = 7.6625(1), b  = 6.9628(1), c  = 11.2821(2) Å, V  = 601.93(1) Å 3 , and 8 formula units in the unit cell. Moreover, we report on the vibrational (IR/Raman) spectroscopy corroborated by structure optimization and simulation of the spectra by DFT methods, as well as thermal analysis on the basis of differential scanning calorimetry and variable-temperature powder X-ray diffraction.

A novel zinc(II) polymer based on pyridine sulfonyl amino acid, namely [Zn(HL)(H 2 O) 2 ] n ·4H 2 O ( 1 ) (HL=(1-carboxylato-2-hydroxypropyl)(pyridin-3-sulfonyl)-threonine), was synthesized by reacting Zn(NO 3 ) 2 ·6H 2 O with H 3 L in a mixed solvent solution of MeCN/EtOH/H 2 O under acidic conditions. Single crystal X-ray diffraction analysis revealed that the polymer 1 crystallized in trigonal crystal system, space group P 3 1 21. Notably, the unit cell of the as-formed polymer 1 contains only one crystallographically independent zinc(II) ion, and the divalent anion ligand HL adopts a coordination pattern of η 1 :η 2 :μ 2 . The zinc(II) central ions are connected by bridging coordination with the HL ligand through pyridyl nitrogen and carboxy oxygen atoms to form an infinite helix chain. Furthermore, numerous hydrogen bonds were observed among these chains, joining them into a 2D supramolecular network. Finally, the complex is stacked along the 3 1 helical axis to yield a three-dimensional supramolecular structure. Additionally, the thermal stability and photoluminescence properties of 1 were determined and discussed.

Despite interesting applications in chemistry, mineralogy and materials science, the rank d of a space group G has never been the main focus of crystallographic investigations before. As a rule, the conventional generating subset of a space group listed in Volume A of International Tables of Crystallography does not fit for correctly estimating d ( G ). The initial generating subset was modified and the code was developed and written in GAP environment to obtain reliable values of d ( G ) (ranging from 2 to 6) for all the 230 space-group types.