Band 229, Heft 6

The gallide SrPdGa 3 was synthesized by melting of the elements in a sealed tantalum tube in an induction furnace. SrPdGa 3 crystallizes with a new structure type which was determined on the basis of single-crystal X-ray diffractometer data: Cmcm , a =643.7(1), b =1044.9(2), c =600.4(1) pm, wR =0.0283, 504 F 2 values, 19 variables. SrPdGa 3 is a new ternary ordering variant of the aristotype BaAl 4 /ThCr 2 Si 2 . The structural relation with ThCr 2 Si 2 and the closely related silicide BaNi 2 Si 2 is discussed on the basis of a group-subgroup relation. The three-dimensional [PdGa 3 ] δ– network is dominated by Pd-Ga and Ga-Ga bonding interactions with 251–256 pm Pd-Ga and 267 pm Ga-Ga distances.

The framework structure of O-mayenite (Ca 12 Al 14 O 33 ) allows the substitution of extra framework oxygen anions by various anions. In this study we present two new anion substituted phases. Oxidation of CN-mayenite leads to the formation of NO 2 -mayenite and, in addition, there are some hints to a very unusual species present in N-mayenite: the hydrazide anion.

The crystal chemistry of anorthite with low content of albite (An 92.0 Ab 3.4 ), part of a rapidly cooled anorthite megacryst occurring in 1940 ejecta from Miyake-jima volcano, Japan, has been investigated using a single-crystal X-ray diffractometer and an electron microprobe analyzer with wavelength dispersive X-ray spectroscopy (EMPA-WDS). The structure was refined in space group P 1̅ and cell parameters, a =8.182(6) Å, b =12.883(4) Å, c =7.092(4) Å, α =93.19(4)°, β =115.91°(4), γ =91.18°(4). The final weighted R-factor is 3.77% for 1549 reflections. Averaged T-O distances are 1.681 Å for T 1 (0), 1.674 Å for T 1 (m), 1.677 Å for T 2 (0) and 1.680 Å for T 2 (m), indicating Al occupancies of 0.501, 0.453, 0.472, and 0.496, respectively. These results suggest that the Al/Si-distribution in the tetrahedral framework is highly disordered (Q OD =0.06), which results in bisection of the c -period in Al/Si ordered anorthites ( c∼ 14 Å). Chemical composition of the refined crystal obtained by EMPA-WDS is (Ca 0.93 Na 0.03 Fe 0.02 □ 0.01 )(Mg 0.01 Al 1.94 Si 2.05 )O 8 . The extra-framework site-populations consist of the following two: (1) A(000) site occupied by Ca (86%), Na (8%), Fe 2+ (4%) and □(2%), and (2) A(zi0) site by Ca (100%). The Al/Si tetrahedral framework is hence pseudo-face-centered in symmetry ( C 1ʩ so that both extra-framework cations and their defects appear to reduce the symmetry of the overall structure to P 1ʮ Although the Al/Si disordered anorthite can be interpreted as a metastable phase, the observed chemical non-stoichiometry may stabilize such a metastable structure by introducing minor -Si 4+ -O-Si 4+ - bonds into the tetrahedral framework and anti-phase-boundary.

Structural and microstructural parameters of seven kidney stones (UKS1–UKS7) retrieved from patients of eastern India were investigated using FTIR spectroscopy, scanning electron microscopy, thermogravimetric analysis and X-ray powder diffractometry. Quantitative phase analysis of kidney stones was performed following the Rietveld method. Crystallite sizes and thermal stability were evaluated from the X-ray peak-broadening analysis and thermogravimetric study. Rietveld analysis of X-ray powder diffraction data indicates that kidney stones are a mixture of phases with whewellite as the major constituent in UKS1–UKS4 and UKS7, whereas the major phase in UKS5 and UKS6 is anhydrous uric acid. The crystallite size of whewellite phase in stones with more than 50 wt% of whewellite (UKS1-UKS4 and UKS7) varies from 149(5) to 182(1) nm, whereas the corresponding sizes of uric acid crystallites in stones with more than 50 wt% of uric acid (UKS5 and UKS6) are 163(2) and 190(3) nm, respectively. Thermogravimetric analysis (TG) of UKS1 reveals that whewellite is stable upto 400 K and above this temperature anhydrous calcium oxalate is formed, which tranforms into calcium carbonate at 750 K and finally to calcium oxide above 970 K. The kidney stone UKS5 with more than 90 wt% of uric acid is stable upto 708 K.

While in both 7-(arylamino)-5-methyl-2-(trifluoromethyl)-[1,2,4]-triazolo-[1,5- a ]pyrimidines, 1 [ 1a : aryl=3,5dichlorophenyl; 1b : aryl=2,4-dichlorophenyl), the strongest intermolecular interactions are N–H···N hydrogen bonds, different acceptor atoms are involved leading to different arrangement of molecules. In the case of 1a , N2A–H2A···N4B and N2B–H2B···N3A hydrogen bonds generate tetrameric units, composed of two molecules of each of the independent molecules, Mol A and Mol B. In the case of 1b , N2A–H2A···N4B and N2B–H2B···N4A hydrogen bonds generate C12 chains of alternate molecules A and B. As well as the strong N–H···N hydrogen bonds, there are also weaker π···π, C–X···π (X=Cl, F and H) and C–H···F interactions in 1a , and π···π, C–X···π (X=H and Cl) and C–H···X (X=F and N) interactions in 1b . In {[7-(4-chlorophenylamino)-5-methyl-2-(trifluoromethyl)-[1,2,4]-triazolo-[1,5- a ]pyrimidine].(H 2 O)}, [1c(H 2 O)] , chains, C 2 2 (16) of alternate molecules of 1c and water are generated from combinations of OW–HW···N and N–H···OW intermolecular hydrogen bonds: also present are π(pyrimidine)···π(chlorophenyl), C–Cl··· π(triazole) and C–F··· π(pyrimidine) interactions. Comparisons with reported [1,2,4]-triazolo-[1,5- a ]pyrimidine structures clearly show variations in the N–H···N hydrogen bonding patterns and the significant influence of the type and position of substituents on the supramolecular assemblies generated.