Volume 240, Issue 3-4

Presented are the flux-growth synthesis and the structural characterization of the series of ternary aluminides R 6 Nb 4 Al 43 , with R representing the rare-earth elements Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Although not new compounds, the structures of R 6 Nb 4 Al 43 have not been unequivocally established to date. This study showcases comprehensive structural work that has been carried out using single-crystal X-ray diffraction methods. The nine title compounds are shown to be isotypic and to crystallize in a hexagonal crystal system with space group P 6 3 / mcm (no. 193). The crystal structure is rather complex and the structure type adopted is known as Ho 6 Mo 4 Al 43 (Pearson symbol hP 106). Structural refinements from single-crystal X-ray diffraction data in all cases help establish the long range crystallographic ordering and no homogeneity width in any of the R 6 Nb 4 Al 43 crystals. There is a monotonic decrease in lattice parameters and unit cell volume with increasing the R -element atomic number, corresponding to the lanthanide contraction and the atomic size reduction across the 4f-series. Anomalous behavior in Yb 6 Nb 4 Al 43 is observed though, whereby a divergence from this trend in decreasing in the unit cell volume is detected. Although not corroborated by magnetic measurements, we posit that the larger than expected the unit cell volume in Yb 6 Nb 4 Al 43 is likely due to Yb 2+ /Yb 3+ mixed-valent state, where the closed-shell 4f 14 electronic configuration for Yb 2+ affects the structural parameters, causing the deviation from the rest of the structures with R 3+ ions.

We study the topological densities of quasiperiodic graphs, whose set of vertices is a cut-and-project set. We use two approaches: a calculation based on the asymptotics of the coordination sequence and a calculation based on the growth forms of the graphs. The main result is an explicit formula expressing the topological density of quasiperiodic graphs in terms of the growth form and cut-and-project construction of the graph. Both approaches are illustrated with three examples: the graphs of vertices of the Penrose and Ammann-Beenker tilings and the Rauzy tiling.

The crystal structure of the highly hydrous analogue of the K-rich gismondine-Sr from Bellerberg paleovolcano, Eifel Mountains, Germany, was studied by single-crystal X-ray diffraction. Electron microprobe analyses (energy-dispersive spectroscopy analyses) provided the empirical formula Sr 1.86 Ca 1.13 Ba 0.02 K 1.47 Na 0.48 (Al 7.79 Fe 0.13 Si 8.08 O 32.025 )·14.97H 2 O. The mineral is orthorhombic, space group P 2 1 2 1 2, a  = 14.1790(2), b  = 10.6062(2), c  = 13.8989(2) Å, V  = 2090.19(6) Å 3 and Z  = 2. The crystal structure of the mineral ( R  = 0.0374 for 4963 unique reflections with I  > 2σ( I )) is characterized by the gismondine-type (GIS) framework with ordered Al and Si atoms in tetrahedral sites. Partially ordered extra-framework cations and water molecules fill the cages of the framework. The higher hydration degree increases the ordering of extraframework cations in the structure. The higher hydration degree increases the ordering of extraframework cations in the structure. The phenomenon is discussed in ion-exchanged GIS zeolites as well as natural zeolites of PHI-type structures.

The regularities of crystal structure organization were studied in a series of para - and ortho -halogenanilines using an approach based on comparison of interaction energies between molecules calculated by an ab initio method. The halogen substituent position in anilines significantly affects intermolecular interactions, differing between para - and ortho -halogen anilines. In para -halogen anilines, the amino group mainly acts as a hydrogen-bond donor, with no significant halogen bonds and weak stacking interactions. In ortho -halogen anilines, the amino group functions as both donor and acceptor, with stronger hydrogen and halogen bonding. Crystal packing analysis shows columnar organization across samples, with zig-zag columns in para -substituted anilines and triple columns in ortho -substituted ones. Overall, halogen bonds play a minor role, mainly connecting neighboring columns.

Trityl-protected triethanolamines were synthesized and their structures evaluated with regard to the planarization of the central nitrogen atom. Although the steric influence of the side groups was found to affect the geometry around the nitrogen atom, this influence was only minor. In addition to the intramolecular interactions, the intermolecular interactions in these crystals were identified on the basis of the solid state structures. These are dominated by short H⋯H contacts and C–H···π interactions. Overall, this study demonstrates the individual influence of distant sterically demanding groups on geometrical parameters and contributes to the understanding of these influences.

Two polymorphs of Cy 3 PAu[SC(OEt)=N(C 6 H 4 Cl-3)], that is a triclinic form ( P 1 ‾ $\overline{1}$ with Z ′ = 1; the α -form) and a monoclinic form ( P 2 1 / c ; Z ′ = 1; the β -form) have been characterised. The molecular structures feature linear P–Au–S coordination geometries with close intramolecular Au⋯O(ethoxy) contacts of 3.1552(17) and 3.097(2) Å for the α - and β -forms, respectively. The major conformational differences between the polymorphs relates to the relative orientations of the thiocarbamato anions and of the cyclohexylphosphane ligands. Computational chemistry shows the molecular structures to be isoenergetic (single-point calculations) and to have practically a zero barrier to interconversion. An analysis of the molecular packing highlights the importance of cyclohexyl-C–H···S(thiolate) and methyl-C–H···π(chlorophenyl) contacts in the crystal of the α -form, and methyl-C–H···π(chlorophenyl) and π(chlorophenyl)···π(chlorophenyl) contacts in the packing of the β -form. While similarities are apparent in the solid-state luminescence spectra, different electronic transitions are responsible for the spectroscopic observations.