X-ray Powder Diagrams Research Articles

Reinvestigation of pure Na-nepheline like compounds obtained from the thermal conversion of zeolite LTA

A polycrystalline sample synthesized through the thermal transformation of zeolite Na-LTA and originally described as standard nepheline was re-investigated. Transmission electron microscopy (TEM) proved the presence of a structure with a tripled c unit-cell parameter compared to that observed in classical nepheline. Consequently, the theoretical X-ray powder diagrams of all known trinepheline compounds were compared with the experimental powder pattern, leading to the conclusion that the material is actually a mixture of two phases. Rietveld refinement against XRPD data using structural models of (a) classical Na-nepheline (S. G. P 6 3 , a = 9.971(3), c = 8.349(2) A) and (b) monoclinic trinepheline (space group P 112 1 , a = 9.995(4), b = 9.963(4), c = 24.988(7) A, γ = 119.75(3) °) resulted in a satisfying agreement between calculated and observed step intensities (χ 2 = 1.96, R wp = 11.3, R p = 8.77). The additional quantitative analyses of the samples obtained in a temperature range of stability of nepheline (900–1100 °C) showed the presence of both structures, and also a gradual increase of the weight fraction of the monoclinic trinepheline phase with increasing temperature.

Predicting crystal structure and habit of organic micro-crystals by experimentally assisted molecular modelling (EAMM). The case of n-octylamino-NBD

Experimentally Assisted Molecular Modelling (EAMM) is an original approach for predicting the structure of organic micro-crystals and deducing their habit in the presence of various solvents and additives. It is applied here in the case of n-octylamino-nitrobenzoxadiazole ( nOA-NBD), a fluorescent compound. This general approach is first of all described and validated by its blind application to three known and closely-related crystals. Then, the whole process is applied to predict the molecular crystal generated by n-octylamino-NBD, including the molecule conformation, its structure (cell parameters, molecular packing, X-ray powder diagrams) and its theoretical plus actual habits in the presence of a solvent ( p-xylene) and two additives (acetic acid and n-dodecane). The conformation of the predicted molecule is validated by comparison with two similar molecules embedded in observable crystals. Then, the choice between two proposed structures (with the same energy and two equiprobable packings) is based on the comparison between experimental and re-computed X-ray powder diffraction diagrams, and also on the interpretation of an actual TEM image in the light of the proposed cell parameters. This choice is confirmed by the comparison between the vapour-grown face development (proposed by the BFDH or the attachment energy models) and the actual face development in a pure solvent. Finally, the actual habit deduced from comparing the crystal attachment energy with the adsorption energy of solvent or additive molecules is validated by SEM images of NBD micro-crystals in presence of the solvent alone or in presence of both additives. In conclusion, the EAMM approach appears to be a decisive tool for quickly simulating structural and habit properties of the molecular crystals, accessible or not by experimentation. Thus, a numerical selection of molecules becomes possible in view of deriving organic materials with predetermined properties, such as the fluorescence properties of the compound considered in the present study.

Structural Characterisation of the Li Argyrodites Li7PS6 and Li7PSe6 and their Solid Solutions: Quantification of Site Preferences by MAS‐NMR Spectroscopy

Li(7)PS(6) and Li(7)PSe(6) belong to a class of new solids that exhibit high Li(+) mobility. A series of quaternary solid solutions Li(7)PS(6-x)Se(x) (0 < or = x < or = 6) were characterised by X-ray crystallography and magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The high-temperature (HT) modifications were studied by single-crystal investigations (both F43m, Z=4, Li(7)PS(6): a=9.993(1) A, Li(7)PSe(6): a=10.475(1) A) and show the typical argyrodite structures with strongly disordered Li atoms. HT-Li(7)PS(6) and HT-Li(7)PSe(6) transform reversibly into low-temperature (LT) modifications with ordered Li atoms. X-ray powder diagrams show the structures of LT-Li(7)PS(6) and LT-Li(7)PSe(6) to be closely related to orthorhombic LT-alpha-Cu(7)PSe(6). Single crystals of the LT modifications are not available due to multiple twinning and formation of antiphase domains. The gradual substitution of S by Se shows characteristic site preferences closely connected to the functionalities of the different types of chalcogen atoms (S, Se). High-resolution solid-state (31)P NMR is a powerful method to differentiate quantitatively between the distinct (PS(4-n)Se(n))(3-) local environments. Their population distribution differs significantly from a statistical scenario, revealing a pronounced preference for P-S over P-Se bonding. This preference, shown for the series of LT samples, can be quantified in terms of an equilibrium constant specifying the melt reaction Se(P)+S(2-) <==>S(P)+Se(2-), prior to crystallisation. The (77)Se MAS-NMR spectra reveal that the chalcogen distributions in the second and third coordination sphere of the P atoms are essentially statistical. The number of crystallographically independent Li atoms in both LT modifications was analysed by means of (6)Li{(7)Li} cross polarisation magic angle spinning (CPMAS).

Qualitative study of supramolecular assemblies of β-cyclodextrin and cholecalciferol and the cobalt (II), copper (II) and zinc (II) ions

A 13C NMR in DMSO-d 6 as solvent, diffuse reflectance spectra and X-ray powder diagram study of the inclusion of vitamin D in β-cyclodextrin and of the ternary assemblies with β -cyclodextrin, vitamin D and metal ions ( e.g. Co(II), Cu(II) and Zn(II)) was carried out to determine the structure of these associations in which the molecular ratios (β -cyclodextrin:vitamin D:metal ions) were 5:1:1 or 10:1:1.

NIVEOLANITE, THE FIRST NATURAL BERYLLIUM CARBONATE, A NEW MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC, CANADA

A new mineral species, niveolanite, the first natural carbonate of beryllium, was found in the Poudrette pegmatite, Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. It is associated with albite, aegirine, natrolite, gonnardite, siderite, petersenite-(Ce), franconite, dawsonite, analcime, quartz, eudidymite, catapleiite, gaidonnayite, monazite-(Ce), calcite, adamsite-(Y), shomiokite- (Y), galena, sphalerite and rutile in cavities; earlier minerals are microcline, nepheline, annite, sodalite and zircon. Niveolanite occurs as soft fibrous (random, matted, radiating, subparallel, sheaf- or spray-like) aggregates up to 2 cm consisting of fibers up to 1.4 cm long and 0.01 mm thick. Rarely, aggregates of acicular crystals up to 1 cm long and 0.03 mm thick, elongate along [001], with a tetragonal or octagonal cross-section, and fibrous pseudomorphs after eudidymite are observed. Individual crystals of niveolanite are colorless and transparent. Aggregates are snow-white to pearl-white, with a silky luster. The density calculated for the empirical formula with 1.66 H 2 O pfu is 2.06, whereas that for the less hydrous variety (1 H 2 O pfu ) is 1.82 g/cm 3 . Niveolanite is optically uniaxial positive, ω 1.469(1), e 1.502(1). The IR spectrum is unique. The averaged chemical composition (Na, K and Ca were determined by electron microprobe, Be by ICP–OES, [CO 2 + H 2 O] from loss on ignition, CO 2 by selective absorption) is: Na 2 O 19.81, K 2 O 0.07, CaO 3.88, BeO 16.65, CO 2 29.81, H 2 O 26.93, total 97.15 wt.%. The empirical formula calculated for 1 C apfu is: (Na 0.94 Ca 0.10 ) ∑1.04 Be 0.98 (CO 3 ) 1.00 (OH) 1.10 ·1.66H 2 O. In moist air, niveolanite strongly absorbs molecular water; the process of its hydration–dehydration is easily reversible. Niveolanite is tetragonal, P 4/ mcc , a 13.1304(19), c 5.4189(11) A, V 934.3(3) A 3 , Z = 8. The strongest ten lines of the X-ray powder diagram [ d in A ( I )( hkl )] are: 13.01(100) (100), 9.20(62)(110), 4.343(27)(300), 3.611(34)(320), 3.269(22)(311), 3.256(95)(400), 2.693(44)(002), 2.605(37)(430,500), 2.489(60)(202), and 2.076(32)(620). The crystal structure was solved using a single crystal and synchrotron radiation, R = 0.0358. Niveolanite represents a new structure-type. Its structure includes isolated, infinite chains of BeO 2 (OH) 2 tetrahedra linked via common OH groups; two other vertices of each Be tetrahedron are shared with (CO 3 ) groups, and Na cations occupy seven-fold polyhedra [NaO 6 (H 2 O)] forming columns. Chains of Be tetrahedra and columns of Na polyhedra are aligned along the c axis, just as broad channels in which H 2 O molecules are located. The structural formula is: {(Na 0.9 Ca 0.1 )[(H 2 O) 0.9 (OH) 0.1 ]}{Be(OH)} (CO 3 )·0–1H 2 O. The idealized formula is: NaBe(CO 3 )(OH)·1–2H 2 O. The mineral was named from Latin niveus , snow-white, and lana , wool, alluding to the visual similarity of its aggregates to snow-white, fluffy flocks of wool. The cotype specimens are deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow, and the Canadian Museum of Nature, Ottawa.

Face-by-face growth of sucrose crystals from aqueous solutions in the presence of raffinose—II: Growth morphology and segregation

Raffinose segregation into sucrose crystals is experimentally determined along with the modifications of the quantitative sucrose growth morphology, which are in turn related to the different growth conditions. ( C raff, σ) morphodromes nicely represent the conflict between the supersaturation and the raffinose concentration in the solution on the growth morphology, while the overall segregation rate is nearly proportional to the linear overall crystal growth rate. Chernov and Burton–Prim–Slichter models, checked to fit our k eff and ln ( k eff - 1 - 1 ) coefficients as a function of the supersaturation and of the mean linear overall growth rate, do not allow to know whether the segregation occurs either by a process dominated by surface integration, or by additive transfer dominated by volume diffusion within the boundary layer. The distribution of segregated raffinose strictly depends on the { h k l} growth sectors and doped crystals contain deformed lattice zones, as it comes out from X-ray powder diagrams.

Pigment Orange 5: crystal structure determination from a non-indexed X-ray powder diagram

Pigment Orange 5, also known as “Dinitroaniline Orange”, is an industrially produced azo pigment. The structure was solved from routinely measured lab X-ray powder data without indexing, by means of a newly developed combination of lattice energy minimization and simultaneous fit to the X-ray powder diagram. Finally, the structure was refined by Rietveld methods using restraints. Pigment Orange 5 crystallizes in space group P21/a with a = 16.365(5) Å, b = 12.874(4) Å, c = 6.924(2) Å, β = 100.143(2)°, Z = 2. The molecules are almost planar and form stacks along the c axis.

Polar binary Zn/Cd-rich intermetallics: Synthesis, crystal and electronic structure of A(Zn/Cd) 13 (A = alkali/alkaline earth) and Cs 1.34Zn 16

The binary alkali/alkaline earth (A) zinc and cadmium (M) compounds that form the NaZn 13 structure type (cubic, space group F m 3 ¯ c ), which were known only from indexed X-ray powder diagrams, have been synthesized from stoichiometric mixtures of the elements and have been structurally characterized using a combination of single crystal data and the Rietveld method. The alkali zinc phases A IZn 13 are only formed with the lighter alkali elements sodium to rubidium ( A I = Na : a = 1227.3(2) pm, R 1 = 0.0205 ; A I = K : a = 1237.9(3) pm, R 1 = 0.0154 ; A I = Rb : a = 1245.19(1) pm, R p = 0.0250 ), whereas the cadmium compounds A I Cd 13 are stable only for the heavier alkali metals potassium to cesium ( A I = K : a = 1379.2(4) pm, R 1 = 0.0118 ; A I = Rb : a = 1384.5(2) pm, R 1 = 0.0139 ; A I = Cs : a = 1392.0(3) pm, R 1 = 0.0381 ). In the crystal structures M-centered M(2)M(1) 12 icosahedra are connected via strong exobonds (forming tetrahedral stars, stella quadrangula) to form a 3D net, in the interstices of which the alkali metals are located in a snub cube 24 coordination. In contrast, the alkaline earth ( A II ) zinc compounds with calcium, strontium and barium ( A II = Ca : a = 1215.4(1) pm, R 1 = 0.0274 ; A II = Sr : a = 1222.2(2) pm, R 1 = 0.0154 ; A II = Ba : a = 1235.8(2) pm, R 1 = 0.0227 ) show statistical defects at the Zn(2) position centering the Zn(1) icosahedra. Both the geometric and the electronic stability of the NaZn 13 structure type, which can be assessed from the pseudo-bandgap calculated using FP-LAPW-DFT methods, are discussed. In contrast to the aforementioned systems, the NaZn 13 type ceases to exist in the binary system Cs–Zn. In this case a phase Cs 1.36Zn 16 with a new structure type but very similar stoichiometry emerges. This compound is the first and only known phase in the system Cs–Zn and crystallizes with a new incommensurably modulated structure: its average structure (orthorhombic, space group Imma, a = 264.2 ( 5 ) pm , b = 720.8 ( 14 ) pm , c = 1760 ( 5 ) pm, R 1 = 0.0198 ) already indicates the representative structural features: in a 3D net of Zn atoms tubular channels filled by the Cs atoms are formed. This Cs filling is, due to geometric requirements, not commensurate with the Zn host structure resulting in a modulated structure with satellite reflections that can be indexed with a q → vector of (0, 0, 0.2755). The final refinement in the superspace group ( P c n 2 ( 0 0 g ) s s o , a = 1760 ( 5 ) pm , b = 720.8 ( 14 ) pm , c = 264.2 ( 5 ) pm, w R main = 0.0550 , w R satellites = 0.140 ) shows a strong occupational and a weak positional modulation of Cs in the channels formed by the Zn partial structure.

New similarity index for crystal structure determination from X-ray powder diagrams

A new similarity index for automated comparison of powder diagrams is proposed. In contrast to traditionally used similarity indices, the proposed method is valid in cases of large deviations in the cell constants. The refinement according to this index closes the gap between crystal structure prediction and automated crystal structure determination. The opportunities of the new procedure have been demonstrated by crystal structure solution of un-indexed powder diagrams of some organic pigments (PY111, PR181 and Me-PR170).

Determination of the structure of the violet pigment C22H12Cl2N6O4 from a non-indexed X-ray powder diagram

The violet pigment methylbenzimidazolonodioxazine, C22H12Cl2N6O4 (systematic name: 6,14-dichloro-3,11-dimethyl-1,3,9,11-tetrahydro-5,13-dioxa-7,15-diazadiimidazo-[4,5-b:4',5'-m]pentacene-2,10-dione), shows an X-ray powder diagram consisting of only ca 12 broad peaks. Indexing was not possible. The structure was solved by global lattice energy minimizations. The program CRYSCA [Schmidt & Kalkhof (1999), CRYSCA. Clariant GmbH, Pigments Research, Frankfurt am Main, Germany] was used to predict the possible crystal structures in different space groups. By comparing simulated and experimental powder diagrams, the correct structure was identified among the predicted structures. Owing to the low quality of the experimental powder diagram the Rietveld refinements gave no distinctive results and it was difficult to prove the correctness of the crystal structure. Finally, the structure was confirmed to be correct by refining the crystal structure of an isostructural mixed crystal having a better X-ray powder diagram. The compound crystallizes in P1, Z=1. The crystal structure consists of a very dense packing of molecules, which are connected by hydrogen bridges of the type N-H...O=C. This packing explains the observed insolubility. The work shows that crystal structures of molecular compounds may be solved by lattice energy minimization from diffraction data of limited quality, even when indexing is not possible.

Mixed pseudohalide complexes of copper(II). Crystal and molecular structure of [Cu(N3)(NCS)(tmen)] n and of [Cu(N3)(NCO)(tmen)]2 (tmen = N,N,N′,N′-tetramethylethylenediamine)

The compounds [Cu(N3)(NSC)(tmen)] n (1), [Cu(N3)(NCO)(tmen)] n (2) and [Cu(N3)(NCO)(tmen)]2 (3) (tmen=N,N,N′,N′-tetramethylethylenediamine) were synthesized and studied by i.r. spectroscopy. Single crystals of compounds (1) and (3) were obtained and characterized by X-ray diffraction. The structure of compound (1) consists of neutral chains of copper(II) ions bridged by a single azido ligand showing the asymmetric end-to-end coordination fashion. Each copper ion is also surrounded by the other three nitrogen atoms; two from one N,N,N′,N′-tetramethylethylenediamine and one from a terminal bonded thiocyanate group. Compound (2) decomposes slowly in acetone and the product formed [Cu(N3)(NCO)(tmen)]2 (3) crystallizes in the monoclinic system (P21). The structure of (3) consists of dimeric units in which the Cu atoms are penta-coordinated and connected by μ(1,3) bridging azido and cyanate ligands. In both cases the five coordinated atoms give rise to a slightly distorted square-based pyramid coordination geometry at each copper ion. The thermal behavior of [Cu(N3)(NSC)(tmen)] n (1) and [Cu(N3)(NCO)(tmen)] n (2) were investigated and the final decomposition products were identified by X-ray powder diagrams.

The Substitution of Germanium for Silicon in AST‐Type Zeolite.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The substitution of germanium for silicon in AST-type zeolite

The substitution of silicon by germanium in the AST zeolite framework type, [Si n Ge 40− n O 80] ∗4(SDA +F −) expressed as unit cell content in its cubic F-centered symmetry, has been studied. Three different kinds of templates, dimethyldiethylammonium, dimethyldiisopropylammonium and isopropyltrimethylammonium cations, were used in the hydrothermal synthesis process in fluoride medium. The products were identified with XRD, MAS NMR, SEM and thermal analysis. The analysis of the X-ray powder diagrams shows that AST crystallizes in different space group symmetries depending on the nature of the SDA and the degree of Ge-substitution. The resonance signals of 19F in MAS NMR experiments for the pure Si- and Ge-end members are at −38.2 and ∼−15 ppm, respectively, indicating that the F −-anion is located as co-template in the double-four-ring (D4R) of the tetrahedral framework. This is confirmed by Rietveld analysis of powder diffraction data of the pure Ge-end member. The peak splitting of the 19F NMR signal in pure GeO 2AST-type material is related to the displacement of F − location inside the D4R. Two more distinct signals at ∼−8 and ∼−19 ppm, respectively, are observed for X-ray pure AST-samples of intermediate compositions and assigned to fluoride in D4R built of 4[GeO 4]- and 4[SiO 4]-tetrahedra (4Ge, 4Si) and to (2Ge, 6Si)-D4R, respectively. An ordered distribution of Ge in the AST-framework is proposed for cubic AST with compositions around Si/Ge=1.5–1 by correlating the intensities of 19F NMR signals and the results from chemical analysis. This model is further confirmed by the quantitative analyses of the corresponding 29Si MAS NMR spectra.

First-Principle Study of the Intercalation Process in the LixV2O5 System

A theoretical study of the lithium intercalated LixV2O5 system has been performed using a dual approach, based on ab initio calculations and experimental data. Two main aspects have been investigated: the atomic structure of each phase and the voltage of a lithium battery with a positive electrode made of LixV2O5. This approach leads to proposal of the full atomic arrangement for the different phases obtained during the reaction. Particularly, a structural arrangement is proposed for the debated ω-Li3V2O5 phase, based on a full simulation of its X-ray powder diagram. For the first time, an antiferromagnetic ordering is envisioned for ζ-Li2V2O5. Finally, a very good simulation of the experimental open circuit voltage (OCV) curve of the battery, from x = 0 to x = 3, is obtained when the magnetic interactions are considered.

A new bidimensional material: Ln 2(CO 3) 3.8 H 2O (Ln=La, Ce) : Synthesis and crystal structure

The slow diffusion through gel in a U-tube of trivalent lanthanide ions with TMA 3−, where TMA 3− stands for [C 6H 3(COO) 3] 3−, afforded single crystals suitable for crystalline resolution. The crystal structure has been solved for the Ce(III) compound and is reported here. The chemical formula is Ce 2(CO 3) 3.8 H 2O and the space group of the crystalline structure is Pccn with: a=8.9421(7) Å, b=9.5292(9) Å, c=16.971(2) Å and Z=4. The structure consists in planes in which the lanthanides ions are connected via bidendate carboxylato groups or μ 2-oxo bridges. The isostructurality of the other compounds has been assumed on the basis of X-ray powder diagram and elementary cell determination.

Synthesis, crystal structure of a new tridimensional family of materials: LnCHA(H 2O) 2·2.5H 2O (Ln=Dy–Yb)

The slow diffusion in water through a H-tube of trivalent lanthanide ions with CHA 3−, where CHA 3− stands for [C 6H 6(COO) 3] 3−, afforded single crystals suitable for crystalline resolution. The crystal structure has been solved for the Er(III) compound and is reported here. The chemical formula is ErCHA(H 2O) 2·2.5H 2O and the space group of the crystalline structure is C2/c with a=13.3944(16) Å, b=12.2501(9) Å, c=15.9220(16) Å, β=92.089(13) and Z=8. The structure presents a complex tridimensional network which can be described as the association of double-sheet network, via μ 2-oxo bridges between Ln 3+ ions. The isostructurality of the other compounds has been assumed on the basis of X-ray powder diagrams and elementary cell determination. The thermal properties of these compounds have been studied and are reported here.

Die Kristallstruktur von Bortriiodid, BI3

Crystal Structure of Boron Triiodide, BI3 Boron triiodide as a micro-crystalline powder was obtained after sublimation of the reaction product of NaBH4 and iodine. An X-ray powder diagram of the temperature-, air-, and light-sensitive compound was collected at –73 °C. According to the results of the Rietveld refinement, the crystal structure of BI3 is isotypic to that of BCl3 (space group P63/m, no. 176, a = 699.09(2), c = 736.42(3) pm). The B–I bond length was determined to be 211.2(8) pm.

Die Kristallstruktur von Bortriiodid, BI3

Crystal Structure of Boron Triiodide, BI3 Boron triiodide as a micro-crystalline powder was obtained after sublimation of the reaction product of NaBH4 and iodine. An X-ray powder diagram of the temperature-, air-, and light-sensitive compound was collected at –73 °C. According to the results of the Rietveld refinement, the crystal structure of BI3 is isotypic to that of BCl3 (space group P63/m, no. 176, a = 699.09(2), c = 736.42(3) pm). The B–I bond length was determined to be 211.2(8) pm.

On the relations between morphological and structural modifications in sucrose crystals grown in the presence of tailor-made additives: effects of mono- and oligosaccharides

A survey is given on morphological modifications induced on sucrose crystals by some tailor-made additives (mono- and oligosaccharides). Special attention is paid to a critical discussion of our analysis of the structure compatibility between additive molecules and surface sites of the crystals, and further of its developments concerning incorporation of additives in the crystal lattice. Finally, it is shown as X-ray powder diagrams of sucrose crystals grown in the presence of these additives, coupled with chromatographic analysis of crystal sectors, proved to be a promising sensitive tool, chiefly to associate the different lattice spacing variations to the absorption anisotropy.

Structure of mono-acid even-numbered β-triacylglycerols

The crystal structure of the beta polymorph of tripalmitin (1,2,3-trihexadecanoylglycerol, beta-PPP) has been determined by single-crystal X-ray diffraction. The molecules crystallize in space group P1; in an asymmetric tuning-fork conformation. This structure and the already-known crystal structures of beta-tricaprin (beta-CCC) and beta-trilaurin (beta-LLL) could be matched in an overlap model. Apart from a difference in chain length, the three structures are almost identical. The overlap model can be used to predict the crystal structure of the other members of the C(n)C(n)C(n)-type (n = even) TAG series reasonably accurately. This is demonstrated by predicting the crystal structure for beta-trimyristin (beta-MMM) and successively comparing the experimental and calculated X-ray powder diagrams.