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This article is the second part of a series dealing with the description and visualization of mathematical functions used to describe a powder diffraction pattern for teaching and education purposes. The first part dealt with the instrumental and sample contributions to the profile of a Bragg peak [Dinnebier & Scardi (2021). J. Appl. Cryst.54, 1811–1831]. The second part, here, deals with the mathematics and physics of the intensity in X‐ray powder diffraction. Scholarly scripts are again provided using the Wolfram language in Mathematica. [ABSTRACT FROM AUTHOR]

A collection of scholarly scripts dealing with the mathematics and physics of peak profile functions in X‐ray powder diffraction has been written using the Wolfram language in Mathematica. Common distribution functions, the concept of convolution in real and Fourier space, instrumental aberrations, and microstructural effects are visualized in an interactive manner and explained in detail. This paper is the first part of a series dealing with the mathematical description of powder diffraction patterns for teaching and education purposes. [ABSTRACT FROM AUTHOR]

The seminal qualitative concepts of chemical bonding, as presented by Walter Kossel and Gilbert Newton Lewis back in 1916, have lasting general validity. These basic rules of chemical valence still serve as a touchstone for validating the plausibility of composition and constitution of a given chemical compound. We report on Ag7Pt2O7, with a composition that violates the basic rules of chemical valence and an exotic crystal structure. The first coordination sphere of platinum is characteristic of tetravalent platinum. Thus, the electron count corresponds to Ag7Pt2O7*e−, where excess electrons are associated with the silver substructure. Such conditions given, it is commonly assumed that the excess electrons are either itinerant or localized in Ag−Ag bonds. However, the material does not show metallic conductivity, nor does the structure feature Ag‐Ag pairs. Instead, the excess electrons organize themselves in 2e−4c bonds within the silver substructure. This subvalent silver oxide reveals a new general facet pertinent to silver chemistry. [ABSTRACT FROM AUTHOR]

The seminal qualitative concepts of chemical bonding, as presented by Walter Kossel and Gilbert Newton Lewis back in 1916, have lasting general validity. These basic rules of chemical valence still serve as a touchstone for validating the plausibility of composition and constitution of a given chemical compound. We report on Ag7Pt2O7, with a composition that violates the basic rules of chemical valence and an exotic crystal structure. The first coordination sphere of platinum is characteristic of tetravalent platinum. Thus, the electron count corresponds to Ag7Pt2O7*e−, where excess electrons are associated with the silver substructure. Such conditions given, it is commonly assumed that the excess electrons are either itinerant or localized in Ag−Ag bonds. However, the material does not show metallic conductivity, nor does the structure feature Ag‐Ag pairs. Instead, the excess electrons organize themselves in 2e−4c bonds within the silver substructure. This subvalent silver oxide reveals a new general facet pertinent to silver chemistry. [ABSTRACT FROM AUTHOR]

Cesium dicyanamide Cs[C2N3] (≡ Cs[N(CN)2] or Cs[dca]) was obtained by a metathesis reaction in form of transparent colorless platelets. The results of single-crystal X-ray structure measurements and refinements (C2/c, Z = 8) with the monoclinic cell parameters a = 932.31(8), b = 1274.67(9), c = 824.94(7) pm, β = 110.803(3)° at −70 °C and a = 939.59(7), b = 1281.58(8), c = 827.57(6) pm, β = 110.610(3)° at 20 °C corroborate earlier results for this compound. The Raman and IR spectra of Cs[C2N3] are presented for the first time and the result compares well with those of NaCs2[C2N3]3. The heat-driven cyclotrimerization process of Cs[C2N3] was studied by thermal analyses (DSC) and temperature-dependent X-ray powder diffraction methods. At 370 °C, its trimerization product Cs3[C6N9] is formed, crystallizing in the orthorhombic space group Pbam with the cell parameters a = 3043.0(3), b = 1052.4(1) and c = 415.21(4) pm for Z = 4. The IR spectrum of this cesium tricyanomelaminate (Cs3[C6N9] or Cs3[TCM]) is presented, but a well-resolved Raman spectrum could not be acquired owing to fluorescence phenomena. An overview about the cyclotrimerization reactions of all pseudo-binary alkali-metal dicyanamides (A[C2N3]) to their corresponding tricyanomelaminates (A3[C6N9]) with A = Li–Cs gives a basis for a discussion of the different thermal and structural characteristics. [ABSTRACT FROM AUTHOR]

Plants and animals that thrive in arid regions utilize the diurnal changes in environmental temperature and humidity to optimize their water budget by combining water-harvesting mechanisms and morphophysiological traits. The Athel tamarisk (Tamarix aphylla) is a halophytic desert shrub that survives in arid, hypersaline conditions by excreting concentrated solutions of ions as droplets on its surface that crystallize into salt crystals and fall off the branches. Here, we describe the crystallization on the surface of the plant and explore the effects of external conditions such as diurnal changes in humidity and temperature. The salt mixtures contain at least ten common minerals, with NaCl and CaSO4·2H2O being the major products, SiO2 and CaCO3 main sand contaminants, and Li2SO4, CaSO4, KCl, K2Ca(SO4)2·H2O, CaMg(CO3)2 and AlNaSi3O8 present in smaller amounts. In natural conditions, the hanging or sitting droplets remain firmly attached to the surface, with an average adhesion force of 275 ± 3.5 µN measured for pure water. Rather than using morphological features of the surface, the droplets adhere by chemical interactions, predominantly by hydrogen bonding. Increasing ion concentration slightly increases the contact angle on the hydrophobic cuticle, thereby lowering surface wettability. Small amounts of lithium sulfate and possibly other hygroscopic salts result in strong hygroscopicity and propensity for deliquescence of the salt mixture overnight. Within a broader context, this natural mechanism for humidity harvesting that uses environmentally benign salts as moisture adsorbents could provide a bioinspired approach that complements the currently available water collection or cloud-seeding technologies. [ABSTRACT FROM AUTHOR]

The reaction of Ni[CO 3 ] with an aqueous solution of the free acid (H 3 O) 2 [B 12 Cl 12 ] leads to green single crystals with the composition Ni(H 2 O) 6 [B 12 Cl 12 ] · 6 H 2 O. This compound crystallizes in the orthorhombic space group Pnnm with a = 1798.86(9), b = 1312.49(7), c = 1373.63(7) pm for Z = 4. Thermal decomposition studies revealed the possibility for a multi-step dehydration process with the loss of all interstitial and cation-hydrating crystal water molecules. Temperature-dependent X-ray powder diffraction (XRPD) measurements show two characterizable degradation products between 30 and 450 °C. Ni(H 2 O) 6 [B 12 Cl 12 ] was obtained at 30 °C after the loss of all interstitial water molecules as pale green powder with a cubic crystal structure ( a = 1700.02(5) pm, Z = 8) and Fm 3 ¯ c as space group, displaying a CsCl-type arrangement. The six water molecules of hydration, which coordinate each Ni 2+ cation show fourfold disorder. Above 450 °C all remaining water molecules have left the sample and the color shifts to yellow indicating the formation of anhydrous Ni[B 12 Cl 12 ]. This water-free salt crystallizes also in the cubic system ( a = 986.71(9) pm, Z = 2), but with Im 3 ¯ as space group. In the crystal structure the Ni 2+ positions are occupied only by 1 / 4 and each of them is coordinated by two [B 12 Cl 12 ] 2− anions attached via two faces offering six chlorine atoms in an octahedral shape. [ABSTRACT FROM AUTHOR]

Light-yellow microcrystalline samples of Cu[dca] ([dca]−≡[N(CN)2]−≡dicyanamide anion) were obtained by blending an in-situ generated aqueous Cu+ brine with stoichiometric amounts of Na[dca] dissolved in water. The crystal structure of Cu[dca] was solved and refined from powder X-ray diffraction (PXRD) data. Cu[dca] crystallizes in the orthorhombic space group Cmcm (no. 63) with the lattice parameters of a=356.28(3), b=611.10(9) and c=1525.87(10) pm. The crystal structure contains undulated chains of alternating Cu+ and boomerang-shaped [N≡C-N-C≡N]− ions with C2 v symmetry running along [100]. It is closely related to that of Ag[dca] crystallizing in space group Pnma (no. 62). The vibrational spectra for Cu[dca] and Cu[dca]2 were recorded exhibiting modes typical for the dicyanamide anion. Comparative DSC/TG measurements were performed for both copper dicyanamides and the cyanide Cu[CN]. [ABSTRACT FROM AUTHOR]

The previously unknown nickel chloride hydroxide phases Ni3Cl2+ x(OH)4- x ·2H2O ( x = 0.26, 0.48, 0.82) have been synthesized in concentrated aqueous NiCl2 solutions and investigated in detail. Crystal structure determination from X-ray powder diffraction data revealed triple chains of distorted, edge-linked NiO6 and NiO3(O/Cl)3 octahedra as the main building blocks. The chains exhibit a layer-like configuration and therefore great structural similarity to nickel-layered hydroxy halides (Cl, Br, I) and β-Ni(OH)2. Increasing chloride content in Ni3Cl2+ x(OH)4- x ·2H2O leads to a reduction of the space group symmetry from C2/ m (12) for x = 0.26 and 0.48 to P $\bar {1}$ (2) for x = 0.82 and to distinct shifts in their thermal, spectral, and magnetic properties. Each solid exhibits a maximum magnetic susceptibility in the range 5.9-9.7 K, which indicates antiferromagnetic ordering. Positive Curie-Weiss temperatures, θ, were found, which points to predominantly ferromagnetic spin-exchange interactions. In addition, broad maxima of the magnetic susceptibility evidence a low-dimensional magnetic character as the most prominent feature of the magnetic properties of the investigated phases. [ABSTRACT FROM AUTHOR]

The crystal structure of ferrous glycine sulfate (a ferroglycine sulfate complex with chemical formula FeSO4(C2H5NO2), a compound extensively used as an iron dietary supplement, was refined from synchrotron X-ray powder diffraction data. The crystal structure of an (so-far unreported) isostructural manganese analogue was also structurally detailed by a Rietveld refinement against the corresponding X-ray powder diffraction pattern. All studied compounds crystallize in the monoclinic P21 space group, building layers of metal cations coordinated by the oxygen atoms of sulfate groups and glycine ligands. Neighboring layers are parallel packed, bonded by hydrogen bonds. The coordination polyhedra around the cations can be regarded as distorted and elongated octahedral, presumably due to severe strains present in the crystal structure of the layers. [ABSTRACT FROM AUTHOR]

Anhydrous zinc hydroxide sulfates are promising precursors for the preparation of pigments and ZnO nanomaterials. The crystal structure of one such compound 5[Zn(OH)2] ·2[ZnSO4] was determined from high resolution laboratory X-ray powder diffraction data by use of a combination of charge flipping, simulated annealing, and difference Fourier analysis. The material crystallizes in the space group P $\bar{1}$ with the lattice parameters of a = 5.4559(2) Å, b = 8.0528(3) Å, c = 8.9275(3) Å, α = 112.697(2)°, β = 85.219(3)°, γ = 95.441(3)°, and a volume of V = 359.76(2) Å3. The basic crystal structure consists of brucite type Zn(OH)2 layers where every sixth octahedral site is vacant. Tetrahedrally coordinated zinc ions are located above and below these vacancies and consecutive layers are bridged by sulfate molecules. The composition of this layered structure can be written as [Zn5VI□(OH)4 ·Zn2IV(OH)6 ·(SO4)2]. Its thermal decomposition was studied by X-ray powder diffraction and thermal analysis. [ABSTRACT FROM AUTHOR]

Two samples of pure NiCl(OH) were produced by hydrothermal synthesis and characterized by chemical analysis, IR spectroscopy, high-resolution laboratory X-ray powder diffraction and scanning electron microscopy. Layers composed of edge-sharing distorted NiCl6 x(OH)6−6 x octahedra were identified as the main building blocks of the crystal structure. NiCl(OH) is isostructural to CoOOH and crystallizes in space group R m [ a = 3.2606 (1), c = 17.0062 (9) Å]. Each sample exhibits faults in the stacking pattern of the layers. Crystal intergrowth of ( Aγ B)( Bα C)( Cβ A) and ( Aγ B)( Aγ B) [C6 like, β-Ni(OH)2 related] stacked layers was identified as the main feature of the microstructure of NiCl(OH) by DIFFaX simulations. A recursion routine for creating distinct stacking patterns of rigid-body-like layers in real space with distinct faults (global optimization) and a Rietveld-compatible approach (local optimization) was realized and implemented in a macro for the program TOPAS for the first time. This routine enables a recursive creation of supercells containing ( Aγ B)( Bα C)( Cβ A), ( Aγ B)( Aγ B) and ( Cβ A)( Bα C)( Aγ B) stacking patterns, according to user-defined transition probabilities. Hence it is an enhancement of the few previously published Rietveld-compatible approaches. This routine was applied successfully to create and adapt a detailed microstructure model to the measured data of two stacking-faulted NiCl(OH) samples. The obtained microstructure models were supported by high-resolution scanning electron microscopy images. [ABSTRACT FROM AUTHOR]

For the first time a complete solid solution series Ni 2 x Mg 2−2 x Cl(OH) 3 of an atacamite type alkaline main group metal chloride, Mg 2 Cl(OH) 3 , and a transition group metal chloride, Ni 2 Cl(OH) 3 , was prepared and characterized by chemical and thermal analysis as well as by Raman and IR spectroscopy, and high resolution laboratory X-ray powder diffraction. All members of the solid solution series crystallize in space group P nam (62). The main building units of these crystal structures are distorted, edge-linked Ni/MgO 4 Cl 2 and Ni/MgO 5 Cl octahedra. The distribution of Ni 2+ - and Mg 2+ -ions among these two metal-sites within the solid solution series is discussed in detail. The crystallization of the solid solution phases occurs via an intermediate solid solution series, (Ni/Mg)Cl 2 x (OH) 2−2 x , with variable Cl: OH ratio up to the 1:3 ratio according to the formula Ni 2 x Mg 2−2 x Cl(OH) 3 . For one isolated intermediate solid solution member, Ni 0.70 Mg 0.30 Cl 0.58 (OH) 1.42 , the formation and crystal structure is presented as well. [ABSTRACT FROM AUTHOR]

In the course of the investigation of glass-induced metal corrosion processes, a microcrystalline sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(H2O)4(OH)2, was detected on a series of antique works of art, and its crystal structure was determined ab initio from high-resolution laboratory X-ray powder diffraction data using the method of charge flipping, simulated annealing, and difference-Fourier analysis (P42/n, a = 8.425 109(97) Å, c = 17.479 62(29) Å, V = 1240.747(35) ų, Z = 8). In the crystal structure, the metal cations are interconnected in a two-dimensional metal-organic framework via the oxygen atoms of the formate, hydroxide, and oxide anions. Doublets of face-sharing square pyramidal Cu2+ polyhedra are linked via a single, central oxide oxygen atom to give a paddle-wheel arrangement, while the Na+ cations are organized in Na2O11 moieties with highly disordered, edge-sharing octahedral coordination. In addition, hydrogen bonding plays an important role in stabilizing the crystal structure. [ABSTRACT FROM AUTHOR]

Almost a century has passed since the pioneering work of Debye, Scherrer, and Hull and their first powder X-ray diffraction experiments in 1916/17. Although these pioneers and many others discovered most of the fundamental concepts in the field of powder diffraction within the first few years, nobody at that time could foresee the development of the computer and its calculating power in the 21st century. The general availability of computing power changed the field of powder diffraction, as Hugo Rietveld showed with his computer-assisted whole powder pattern fitting concept around fifty years after the first powder diffraction patterns were observed. Nowadays, much more complex algorithms are used to solve and identify crystal structures from powders. The intention of this historical review is to show some of the most important developments from the viewpoint of the authors in the field of powder diffraction in the last century, from the beginnings of the first transmission experiments and the determination of simple cubic crystal structures to the techniques of today allowing for the refinement of thousands of atoms within one unit cell. [ABSTRACT FROM AUTHOR]

The new low valent iridiumindiumoxogallate Ir2In12Ga4O15 was prepared by heating intimate mixtures of Ir, In, In2O3, and Ga2O3 in a platinum crucible under an atmosphere of argon (1400 K, 70 h). The compound has an orange color. X-ray powder diffraction patterns can be indexed on the basis of a primitive orthorhombic unit cell with lattice parameters a = 1954.5(1) pm, b = 674.0(1) pm, and c = 745.9(1) pm. The crystal structure of Ir2In12Ga4O15 was solved from powder diffraction data and refined using the Rietveld method ( Pnn2, R(prof.) = 4.4 %, R(int.) = 2.5 %). Ir2In12Ga4O15 is according to [IrIn5In2/2]9+2[GaO4]5-2[Ga2O7]8- an ortho-gallate- pyro-gallate with chains of corner sharing [IrIn7]9+ polyhedra, [GaO4]5-2 tetrahedra, and [Ga2O7]8- double tetrahedra. The Ir-In distances within the IrIn7 polyhedra are shorter than in Ir-In intermetallic phases and lie between 256-261 pm. [ABSTRACT FROM AUTHOR]

For the first time a basic transition-metal hydrate, Ni3Cl2.1(OH)3.9•4H2O, is found to be isostructural to a main-group metal phase, Mg3Cl2.0(OH)4.0-4H2O. The Ni phase was found as crystalline solid in the course of investigations into the formation of basic nickel(II) chloride phases at 25 and 40 °C in alkaline, concentrated nickel(II) chloride solutions. Ni3Cl2.1(OH)39•4H2O was characterized by thermal analysis, IR spectroscopy, scanning electron microscopy, and X-ray powder diffraction. The crystal structure was determined from high-resolution laboratory X-ray powder diffraction data. Ni3Cl2.1(OH)3.9•4H2O crystallizes in space group C2/m (12) with Z = 1, a = 14.9575(4) Å, b = 3.14131l) Å, c = 10.4818(5) Å,ß = 101.482(1)°, and V = 482.S0(3) ų. The main building unit of the structure is an infinite triple chain of edge-linked distorted NiO6 octahedra. These chains are separated by interstitial one-dimensional zigzag chains of disordered Cl- ions and H2O molecules. The crystal structures of Ni3Cl2.1(OH)3.9-4H2O and the isostructural magnesium salt hydrate Mg3Cl2(OH)4. 4H2O (2--1--4 phase) are compared in detail. [ABSTRACT FROM AUTHOR]

The application of rotational symmetry modes to quantitative rigid-body analysis is demonstrated for octahedral rotations in Mg(H2O)6RbBr3. Rigidbody rotations are treated as axial-vector order parameters and projected using group-theoretical methods. The high-temperature crystal structure of the Mg(H2O)6RbBr3 double salt consists of a cubic perovskite-like corner-sharing network of RbBr6 octahedra with isolated MgO6 octahedra at the perovskite A sites. A phase transition occurs at 411 K upon cooling, whereupon the MgO6 octahedra experience a substantial rigid-body rotation, the RbBr6 octahedra are translated but not rotated, and both types of octahedra become slightly distorted. The MgO6 rotation has three orthogonal components associated with the X-5, Γ4 + and X1 - irreducible representations of the parent Pm3m space-group symmetry which, given the weakly first-order character of the transition, appear to be strongly coupled. Parametric and sequential refinements of the temperature-dependent structure were conducted using four model types: (1) traditional atomic xyz coordinates for each atom, (2) traditional rigid-body parameters, (3) purely displacive symmetry modes and (4) rigid-body rotational symmetry modes. We demonstrate that rigid-body rotational symmetry modes are an especially effective parameter set for the Rietveld characterization of phase transitions involving polyhedral rotations. [ABSTRACT FROM AUTHOR]

Parametric refinement is used for the simultaneous modeling of a series of diffraction data, replacing single independent parameters with physical or empirical equations that are valid for the full sequence of data. For the parametric treatment of diffraction data at high pressure, pressure-dependent constraints can be introduced in the form of an equation of state (EoS). However, the parameterization needs inverse functions of the EoS and most of them are not analytically invertible. In order to overcome this drawback, Taylor series expansions of different orders of the Vinet EoS were calculated and analytically inverted. It is shown that the inverted third-order Vinet EoS approximation, in its volume and linearized version, is applicable to a wide range of materials under high pressure. [ABSTRACT FROM AUTHOR]

Parametric refinement is used for the simultaneous modeling of a series of diffraction data, replacing single independent parameters with physical or empirical equations that are valid for the full sequence of data. For the parametric treatment of diffraction data at high pressure, pressure-dependent constraints can be introduced in the form of an equation of state (EoS). However, the parameterization needs inverse functions of the EoS and most of them are not analytically invertible. In order to overcome this drawback, Taylor series expansions of different orders of the Vinet EoS were calculated and analytically inverted. It is shown that the inverted third-order Vinet EoS approximation, in its volume and linearized version, is applicable to a wide range of materials under high pressure. [ABSTRACT FROM AUTHOR]

Dehydration is an important process which affects the chemical, physical and mechanical properties of materials. This article describes the thermal dehydration and decomposition of the Sorel cement phase 3Mg(OH)2 ·MgCl2 ·8H2O, studied by in situ synchrotron X-ray powder diffraction and thermal analyses. Attention is paid on the determination of the chemical composition and crystal structure of the lower hydrates, identified as the phases 3Mg(OH)2 ·MgCl2 ·5.4H2O and 3Mg(OH)2 ·MgCl2 ·4.6H2O. The crystal structure of 3Mg(OH)2 ·MgCl2 ·4.6H2O is solved and refined by the Rietveld method and a structural model for the 3Mg(OH)2 ·MgCl2 ·5.4H2O phase is given. These phases show statistical distribution of water molecules, hydroxide and chloride anions positioned as ligands on the magnesium octahedra. A structural scheme of the temperature induced transformations in the thermal range from 25 to 500 °C is presented. [ABSTRACT FROM AUTHOR]

Docetaxel is a semisynthetic analogof the taxane paclitaxel, pivotalfor the treatment of various types of cancer. Minor differences inits chemical structure give docetaxel a slightly better water solubilityprofile when compared to paclitaxel. An understanding of the hydrogen-bondingnetwork in docetaxel is therefore imperative if an explanation forits improved solubility over its predecessor is to be sought. Newcrystalline forms for solvated (ethanol), hydrated, and anhydrousdocetaxel are reported. The crystal structures were determined bysingle crystal synchrotron and laboratory powder X-ray diffractionexperiments on crystalline materials resulting from polymorph screeningtests in various solvents. Variable-temperature experiments were carriedout over ranges between 20 and 130 °C, with subsequent loss ofcrystal water at 70 and 90 °C. The resulting structures are discussedin terms of their intermolecular interactions, molecular conformations,and packing motifs. A rare hydrogen-bonding motif, observed betweencarbamate and tetracyclic ether groups, was found in the packing ofall phases of docetaxel. Subtle but significant changes in structuralhydrogen bonding motifs are discussed and their differences supportedand visualized by Hirshfeld surface calculations and related two-dimensionalfingerprint plots. [ABSTRACT FROM AUTHOR]

In the course of investigations relating to magnesia oxysulfate cement the basic magnesium salt hydrate 3Mg(OH)2 ·MgSO4 ·8H2O (3-1-8 phase) was found as a metastable phase in the system Mg(OH)2-MgSO4-H2O at room temperature (the 5-1-2 phase is the stable phase) and was characterized by thermal analysis, Raman spectroscopy, and X-ray powder diffraction. The complex crystal structure of the 3-1-8 phase was determined from high resolution laboratory X-ray powder diffraction data [space group C2/ c, Z = 4, a = 7.8956(1) Å, b = 9.8302(2) Å, c = 20.1769(2) Å, β = 96.2147(16)°, and V = 1556.84(4) Å3]. In the crystal structure of the 3-1-8 phase, parallel double chains of edge-linked distorted Mg(OH2)2(OH)4 octahedra run along [-110] and [110] direction forming a pattern of crossed rods. Isolated SO4 tetrahedra and interstitial water molecules separate the stacks of parallel double chains. [ABSTRACT FROM AUTHOR]

Laboratory X-ray powder diffraction data were used to investigate the dehydration process of magnesium bromide hexahydrate in the temperature range 300 K ≤ T ≤ 420 K. By heating of the as synthesized hexahydrate (MgBr2 ·6H2O, observed in the temperature range 300 K ≤ T ≤ 349 K), three lower hydrates can be obtained in overlapped temperature regions: MgBr2 ·4H2O (332 K ≤ T ≤ 367 K), MgBr2 ·2H2O (361 K ≤ T ≤ 380 K) and MgBr2 ·H2O (375 K ≤ T ≤ 390 K). Although the crystal structure of the hexahydrate was published almost eighty years ago, there are no data on the structures of the lower hydrates. The crystal structures are reported and are found to be isotypical with the structures of the respective chlorides. The structure of MgBr2 ·6H2O is characterized by discrete Mg(H2O)6 octahedra and is the only hydrate of this group that contains unbonded Br- anions. MgBr2 ·4H2O is composed of discrete MgBr2(H2O)4 octahedra, and the structure was found to be disordered. The crystal structure of MgBr2 ·2H2O is formed by single chains of edge-sharing MgBr4(H2O)2 octahedra, while in the case of MgBr2 ·H2O double chains of edge-shared MgBr5H2O are formed. By increasing the temperature, as expected, positive thermal expansion was evidenced. Thermal expansion coefficients, based on the changes of the unit cell parameters, were derived for the following hydrates: MgBr2 ·6H2O, MgBr2 ·4H2O, and MgBr2 ·2H2O. [ABSTRACT FROM AUTHOR]

The crystal structures of four polymorphs of the pesticide dithianon (5,10-dihydro-5,10-dioxonaphtho[2,3- b]-1,4-dithiine-2,3-dicarbonitrile) have been solved from powder diffraction data and refined using the Rietveld method. Three polymorphs crystallize in non-centrosymmetric space groups. Two polymorphs have Z′ > 1. The structures are assembled via interactions between carbonyl groups of quinoid fragments into layers which further interact only by weak interactions. [ABSTRACT FROM AUTHOR]

One of the main phases formed at the beginning of the carbonation reaction of cementitious building materials is the calcium hemicarboaluminate (abbreviated as Hc). This AFm (shorthand for hydrated calcium aluminate phases structurally related to hydrocalumite) phase was synthesized, crystallized and then studied by synchrotron X-ray powder diffraction and micro-Raman spectroscopy. At room temperature and standard experimental conditions two major cementitious phases were detected, the Hc phase (as a major phase) and carbonated calcium hemicarboaluminate (abbreviated as cHc). By increasing the temperature the Hc form transforms into cHc. The crystal structures of these important AFm phases were successfully solved and refined in the space group of the trigonal crystal system. Hc has the unit-cell parameters a = 5.7757 (1) and c = 48.812 (2) Å, and cHc the unit-cell parameters a = 5.7534 (1) and c = 46.389 (1) Å. The two crystal structures are composed of positively charged main layers, [Ca4Al2(OH)12]2+, and negatively charged interlayers, [OH2 n(CO3)1 − n·4H2O]2−. The structure of the main layers is typical of the AFm family. Conversely, the interlayer region has a characteristic structure built up from water molecules and statistically distributed anions. In the interlayer, the Hc carbonate and hydroxyl anions are distributed in a 0.25:0.5 ratio, whereas the ratio of the anions in the cHc interlayers is 0.4:0.2. [ABSTRACT FROM AUTHOR]

2,4-Dioxo-1,3-diazetidine-1,3-bis(methyl- m-phenylene) diisocyanate (dimerized toluene-2,4-diisocyanate, TDI) is one of the most widely used aromatic diisocyanates in the polymer industry, and it crystallizes in at least two polymorphic forms (form A and form B) depending on reaction conditions. The crystal structures of the two forms were determined from high-resolution laboratory X-ray powder diffraction data using simulated annealing and Rietveld refinement. In spite of a marked structural similarity between them, significant discrepancies in the physical properties of the two forms prompted analysis of their partitioned energy terms in an effort to better our understanding of the driving force behind such differences in behaviour. [ABSTRACT FROM AUTHOR]

A quenchable new high-pressure-high-temperature modification of antimony(III) oxide, γ-Sb2O3, has been obtained at hydrostatic pressures of 9-11 GPa and temperatures of 573-773 K. Its crystal structure has been determined from high-resolution synchrotron powder diffraction data. γ-Sb2O3 consists of three-dimensionally cross-linked infinite chains of SbO3 E units ( E = lone pair) with the chains forming tetragonal rod-packing. The underlying topology of γ-Sb2O3 (3,3T8) is found very rarely in inorganic structures; it is realised only for the polyanion [Si4O4N6]10− that occurs in the Ce4(Si4O4N6)O structure type. The structural relation to the two previously known polymorphs of Sb2O3 at ambient pressure, valentinite and senarmontite is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The solid-state phase transformation of different polymorphic forms of copper phthalocyanine to the thermodynamically most stable β-modification was investigated so as to evaluate the influence of mixtures of different polymorphs and additives upon the order of the reaction from isothermal X-ray powder diffraction data. The data were analysed by sequential Rietveld refinement and the results evaluated using both Avrami and Arrhenius equations. The order of the reaction was significantly influenced by the availability of initially present β-copper phthalocyanine and both the nucleation rate and dimensionality of crystal growth depended strongly on sample composition and reaction temperature. [Copyright &y& Elsevier]

In a systematic approach, the ability of the Maximum Entropy Method (MEM) to reconstruct the most probable electron density of highly disordered crystal structures from X-ray powder diffraction data was evaluated. As a case study, the ambient temperature crystal structures of disordered α-Rb2[C2O4] and α-Rb2[CO3] and ordered δ-K2[C2O4] were investigated in detail with the aim of revealing the `true' nature of the apparent disorder. Different combinations of F (based on phased structure factors) and G constraints (based on structure-factor amplitudes) from different sources were applied in MEM calculations. In particular, a new combination of the MEM with the recently developed charge-flipping algorithm with histogram matching for powder diffraction data (pCF) was successfully introduced to avoid the inevitable bias of the phases of the structure-factor amplitudes by the Rietveld model. Completely ab initio electron-density distributions have been obtained with the MEM applied to a combination of structure-factor amplitudes from Le Bail fits with phases derived from pCF. All features of the crystal structures, in particular the disorder of the oxalate and carbonate anions, and the displacements of the cations, are clearly obtained. This approach bears the potential of a fast method of electron-density determination, even for highly disordered materials. All the MEM maps obtained in this work were compared with the MEM map derived from the best Rietveld refined model. In general, the phased observed structure factors obtained from Rietveld refinement (applying F and G constraints) were found to give the closest description of the experimental data and thus lead to the most accurate image of the actual disorder. [ABSTRACT FROM AUTHOR]

The diffraction-line broadening exhibited by three different Pb3O4 phases was studied at ambient and elevated pressures. The broadening indicates strongly anisotropic microstrain, which was interpreted in terms of (local) stress variations in association with strongly anisotropic elastic properties. In particular, making use of the anisotropic compressibility of Pb3O4 determined on the basis of the present data, the pressure fluctuations in the employed diamond anvil cell due to non-hydrostatic conditions of the sample were estimated. [ABSTRACT FROM AUTHOR]

The crystal structure of zolpidem hemitartrate hemihydrate (I, Form E) has been solved from high-resolution laboratory powder diffraction data. It crystallizes in the orthorhombic P212121 space group with a = 22.4664(6) Å, b = 26.0420(7) Å, and c = 7.4391(1) Å. Protonation of zolpidem molecules could not be unambiguously determined. Thermal stability of Form E has been investigated by TG–DTA and in situ by temperature resolved X-ray powder diffraction. Water loss occurs between 50°C ≤ t ≤ 100°C while structure decomposition commences at approximately 120°C yielding zolpidem tartrate (II) and pure zolpidem base (III) in approximately equimolar amounts. Crystal structures of II and III have been solved simultaneously from a single powder pattern of thermally decomposed I. Zolpidem tartrate crystallizes in the orthorhombic P212121 space group with a = 19.9278(8) Å, b = 15.1345(8) Å, and c = 7.6246(2) Å (at 140°C). Zolpidem base crystallizes in the orthorhombic Pcab space group with a = 9.9296(4) Å, b = 18.4412(9) Å, and c = 18.6807(9) Å (at 140°C). In the reported crystal structures zolpidem molecules form stacks through π–π interaction or dipole–dipole interactions while tartrate moieties, if present, form hydrogen bonded chains. Water molecule in I forms a hydrogen bond to the imidazole nitrogen atom of the zolpidem molecule. Free space in the crystal structure of I could allow for the additional water molecules and thus a variable water content. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:871–878, 2010 [ABSTRACT FROM AUTHOR]

Abstract: The thermal behavior of AgNCO (silver isocyanate) has been studied via thermal analysis, optical spectroscopy, X-ray powder diffraction and transmission electron microscopy. Upon quenching the high temperature polymorph (HT-AgNCO) to room temperature, a new modification has been obtained (q-AgNCO). Its crystal structure was solved from X-ray powder diffraction data and refined by the Rietveld method (Pmmn (no. 59), a =3.579(3)Å, b =5.777(4)Å, c =5.807(2)Å, V =120.08(3)Å3, Z =2, T =295K). The structure consists of chains of Ag+ ions bridged by isocyanate units. HT-AgNCO exists between T =135°C and the melting/decomposition point and exhibits virtually free rotation of the complex anions. According to preliminary single-crystal studies, HT-AgNCO (C2/m, a =5.87Å, b =3.51Å, c =5.81Å, ß =105.953°, Z=2, T =373K) is structurally related to α-NaN3. The crystal structures of both, HT-AgNCO and q-AgNCO have been compared with that of the room temperature modification (RT-AgNCO). The thermal behavior and the ionic conductivity of AgNCO are discussed with respect to the related compounds AgN3 and KSCN. Decomposition of AgNCO proceeds in distinct steps, as seen from TGA, and results in the formation of nanoparticles of elemental silver and an amorphous polymer consisting of C, N and O, only. [Copyright &y& Elsevier]

Abstract: The crystal structure of Rb2SeO4 in its high-temperature phase is reported for the first time. Powder diffraction data collected at T =898K show that it is hexagonal (a =6.3428(1)Å, c =8.5445(1)Å, V =297.71(1)Å3, space group P63/mmc (194), Z =2) and is isostructural to Tl2SeO4, thus belonging to the α-K2SO4 structure type. DSC measurements indicate that the phase transition occurs at T =818K. [Copyright &y& Elsevier]

The crystal structures of the analgesic compounds anhydrous naloxone and naltrexone hydrochloride were determined ab initio from high resolution laboratory X-ray powder diffraction data. Both compounds crystallize in the orthorhombic space group P212121 with lattice parameters of a = 14.6588(10) Å, b = 17.4363(9) Å, c = 7.96200(22) Å, and V = 2035.06(23) Å3 for naloxone hydrochloride and a = 15.4560(5) Å, b = 14.9809(4) Å, c = 7.84121(18) Å, and V = 1815.58(11) Å3 for naltrexone hydrochloride. The crystal structure of anhydrous naloxone hydrochloride forms one-dimensional chains through hydrogen bonds. In the crystal structure of anhydrous naltrexone hydrochloride, two-dimensional sheets are formed by hydrogen bonds. The dehydration processes of naloxone hydrochloride dehydrate and naltrexone hydrochloride tetrahydrate was analyzed by DTA, DSC, TG, and MG. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3316–3323, 2007 [ABSTRACT FROM AUTHOR]

The crystal structure with the idealized formula Mg3(OH)5Cl·4H2O, the so-called F5 phase according to 5Mg(OH)2·MgCl2·8H2O in the system MgCl2–MgO–H2O, has been solved ab initio from high-quality laboratory powder diffraction data at room temperature. The F5 phase is structurally related to 3Mg(OH)2·MgCl2·8H2O (F3 form). The F5 phase consists of infinite triple chains with one Mg(OH)6 and two Mg(OH)4(OH2)2 octahedra as building units intercalated by chlorides, which are partly substituted by disordered hydroxides in the real structure. The F5 phase is of technological importance as the most important binder phase in Sorel cements. Knowledge of the crystal structure enables the full quantitative phase analysis of magnesia cements for the first time, which turns out to be very helpful in the search for possible causes of broken or bleached magnesia floors. Two real-life examples are given. [ABSTRACT FROM AUTHOR]

High-quality in situ synchrotron powder diffraction data have been used to investigate the decomposition products of bischofite in the temperature range 298 ≤ T≤ 873 K. At least eight phases could be identified: MgCl2· nH2O ( n = 1, 2, 4 and 6), MgOHCl· nH2O (0 ≤ n≤ 1.0), MgCl2 and MgO. The crystal structures of three magnesium chloride hydrates MgCl2· nH2O ( n = 1, 2, 4) were determined ab initio, replacing published Rietveld refinements from low-quality powder diffraction data based on similarity criteria. MgCl2·4H2O was found to be disordered and has been correctly determined for the first time. The crystal structures of bischofite and MgCl2·4H2O consist of discrete Mg(H2O)6 and MgCl2(H2O)4 octahedra, respectively. The crystal structure of MgCl2·2H2O is formed by single chains of edge-sharing MgCl2(H2O)4 octahedra, while in the case of MgCl2·H2O double chains of edge-sharing MgCl(H2O)5 octahedra are found. The phases in the system MgCl2–H2O are intermediates in the technologically important process of MgO and subsequently Mg production. The same phases were recently found to be of key importance in the understanding of cracks in certain magnesia concrete floors. [ABSTRACT FROM AUTHOR]

The crystal structure of silver azide (AgN3) in its high-temperature (HT) modification was determined from X-ray powder diffraction data, recorded at T = 170 °C and was further refined by the Rietveld method. The structure is monoclinic (P21/c (No. 14), a = 6.0756(2) Å, b = 6.1663(2) Å, c = 6.5729(2) Å, β = 114.19(0)°, v = 224.62(14) ų, Z = 4) and consists of two-dimensional Ag and N containing layers in which the silver atoms are coordinated by four nitrogen atoms exhibiting a distorted square coordination environment. These sheets are linked together by weaker perpendicular Ag-N contacts, thus forming a 4 + 2 coordination geometry around the silver atoms. The phase transition has been characterized by DTA, DSC, and measurement of the density, as well as of the ionic conductivity. Both, the room-temperature and the HT phase are electrically insulating. This fact is getting support by DFT band structure calculations within the generalized gradient approximation, using the PBE functional. On the basis of the DFT band structure, the bonding characteristics of both phases are essentially the same. Finally, the implication of the existence of a low-symmetry HT-phase in a crystalline explosive concerning decomposition mechanisms is discussed. [ABSTRACT FROM AUTHOR]

Na xCuO2 ( x≃ 1.6) has been synthesized for different compositions x, resulting in both commensurate and incommensurate composite crystals. The crystal structures are reported for two incommensurate compounds ( x = 1.58 and 1.62) determined by Rietveld refinements against X-ray powder diffraction data. The incommensurate compounds and commensurate Na8Cu5O10 ( x = 1.6) are found to possess similar structures, with valence fluctuations of Cu2+/Cu3+ as the origin of the modulations of the CuO2 subsystems; the displacive modulations of Na being defined by the closest Na—O contacts between the subsystems. A comparison of the structure models obtained from single-crystal X-ray diffraction, synchrotron-radiation X-ray powder diffraction and X-ray powder diffraction with Cu Kα1 radiation indicates that single-crystal X-ray diffraction is by far the most accurate method, while powder diffraction with radiation from an X-ray tube provides the least accurate structure model. [ABSTRACT FROM AUTHOR]

We report on the first synthesis of a potassium orthoselenate(VI), K6(SeO4)(SeO5), and the structure determination from synchrotron powder diffraction data. The title compound crystallizes in the tetragonal space group P41212 with a = 8.1259(1) Å, c = 17.4953(2) Å, V = 1155.21(2) ų, and Z = 4. Selenium displays two different complex anions, tetrahedral SeO42- and trigonal-bipyramidal SeO54-. When the formula is reduced to A3B, the spatial arrangement of the constituting building units can be derived from the Li3Bi type of structure. [ABSTRACT FROM AUTHOR]

The volcanic exhalation product chlorartinite, [Mg2(CO3)(H2O)(OH)]Cl·H2O, has recently been found to be a minor, and in some samples a major, component of magnesia floors for industrial use. In order to be able to perform quantitative phase analysis using the Rietveld method, its crystal structure was determined from high-resolution synchrotron powder diffraction data by the global optimization technique of simulated annealing and Rietveld refinement. The final Rp and Rwp values are 5.23% and 6.56%, respectively. Chlorartinite crystallizes in the rhombohedral space group R3 c (No. 161), with a = 23.14422 (16) Å, c = 7.22333 (5) Å, V = 3350.84 (5) Å3, Z = 18. The building units of chlorartinite consist of MgO6 octahedra forming 15-membered puckered rings which are interconnected by CO3 triangular moieties. The rings are stacked to form a honeycomb-like three-dimensional framework structure with large isolated channels. Within the channels, free chlorine atoms and disordered water molecules are located. [ABSTRACT FROM AUTHOR]

The crystal structures of divalent metal salts of trifluoromethyl sulfonic acid (`trifluoromethyl sulfonates') M(SO3CF3)2 ( M = Mg, Ca, Ba, Zn, Cu) were determined from high-resolution X-ray powder diffraction data. Magnesium, calcium and zinc trifluoromethyl sulfonate crystallize in the rhombohedral space group . Barium trifluoromethyl sulfonate crystallizes in the monoclinic space group and copper trifluoromethyl sulfonate crystallizes in the triclinic group . Within the crystal structures the trifluoromethyl sulfonate anions are arranged in double layers with the apolar CF3 groups pointing towards each other. The cations are located next to the SO3 groups. The symmetry relations between the different crystal structures have been analysed. [ABSTRACT FROM AUTHOR]

The crystal structures of three polymorphic phases of rubidium trifluoromethyl sulfonate (RbSO3CF3, rubidium ‘triflate’) were solved from X-ray powder diffraction data. At room temperature, rubidium triflate crystallizes in the monoclinic space group Cm with lattice parameters of a = 19.9611(5) Å, b = 23.4913(7) Å, c = 5.1514(2) Å, β = 102.758(2)°; Z = 16. At T = 321 K, a first-order phase transition occurs toward a monoclinic phase in space group P21 with lattice parameters at T = 344 K of a = 10.3434(5) Å, b = 5.8283(3) Å, c = 5.1982(3) Å, β = 104.278(6)°; Z = 2). At T = 461 K, another phase transition, this time of second order, occurs toward an orthorhombic phase in space group Cmcm with lattice parameters at T = 510 K of a = 5.3069(2) Å, b = 20.2423(10) Å, c = 5.9479(2) Å; Z = 4. As a common feature within all three crystal structures of rubidium triflate, the triflate anions are arranged in double layers with the lipophilic CF3 groups facing each other. The rubidium ions are located between the SO3 groups. The general packing is similar to the packing in cesium triflate. Rubidium triflate can be classified as a solid electrolyte with a specific ionic conductivity of σ = 9.89 × 10-9 S/cm at T = 384 K and σ = 3.84 × 10-6 S/cm at T = 481 K. [ABSTRACT FROM AUTHOR]

Abstract: In order to resolve discrepancies between the valence state +IV as assigned to bismuth in Ag2BiO3 based on structural arguments, and its physical properties, we have reinvestigated this compound. By single crystal structure analyses at different temperatures in combination with neutron powder diffraction, systematic twinning was recognized. Thus, the former model describes the average structure of the twinned crystal. By refining the data set assuming an inversion twin, the correct crystallographic description has been achieved (Ag2BiO3, , , , , ). In this model, there are two distinct crystallographic sites for bismuth, allowing for a charge ordering according to Ag2Bi3+Bi5+O3. Average distances in BiO6-octahedra are 2.34 and 2.13 Å, for Bi3+ and Bi5+, respectively. The bond valence sums are calculated as 3.08 and 5.06. This charge ordering at room temperature fully explains the semiconducting behavior and diamagnetism of the compound. Moreover, temperature dependent neutron powder diffraction (2–298 K) revealed a monoclinic distortion of the lattice upon cooling that was confirmed independently by single crystal investigations (100 K). The structure was refined in Pn (, , , , , ). Except for a tilting of the BiO6-octahedra with oxygen atoms at common vertices acting as hinges, no but slight structural changes have been observed. The bismuth charge ordering is unaffected by the orthorhombic/monoclinic phase transition. [Copyright &y& Elsevier]

Abstract: has been studied at high temperatures by in situ X-ray powder diffraction in an inert atmosphere. Lattice parameters indicate an anisotropic thermal expansion up to , followed by an approximately isotropic expansion up to . It is proposed that is the temperature of a second-order phase transition between the known room temperature form with space group and a high-temperature form with space group Pcab. Above a minority phase develops in the sample that was identified as the containing compound , while the anisotropic expansion along suggests that stoichiometric transforms into with interstitial oxygen located between the layers. With an onset at all of the transforms into . [Copyright &y& Elsevier]

We present a (re)investigation of the hexaoxometalates Li8MO6 (M = Sn, Pb, Zr, Hf) and Li7MO6 (M = Nb, Ta, Sb, Bi). Lithium motion and ionic conductivity in the hexaoxometalates were studied using impedance spectroscopy (for Li7MO6, M = Sb, Bi, Ta) and 3Li and 7Li solid-state nuclear magnetic resonance (for Li7TaO6). The NMR data indicate a considerable exchange of Li among the tetrahedral and octahedral voids even at ambient temperature. In an investigation of the crystal structures using laboratory and synchrotron X-ray powder diffraction techniques, the structures of Li7TaO6, Li7NbO6, and Li7SbO6 could be solved and refined. All three reveal a triclinic metric (Li7SbO6, triclinic, P1macr;, a = 5.38503(6) Å3, b = 5.89164(7) Å, c = 5.43074(6) Å, α = 117.2210(6)°, β = 119.6311(6)°, γ = 63.2520(7)°, V = 127.454(3) Å 3, Z = 1; Li7NbO6, triclinic, P1macr;, a = 5.37932(9) Å, b = 5.91942(11) Å, c = 5.37922(9) Å, α = 117.0033(9)°, β = 119.6023(7)°, γ = 63.2570(9)°, V= 126.938(4) Å3, Z = 1; Li7TaO6, triclinic, P1macr;, a = 5.38486(2) Å, b = 5.92014(3) Å, c = 5.38551(2) Å, α = 117.0108(2)°, β = 119.6132(2)°, γ = 63.2492(2)°, V= 127.208(1) Å3, Z= 1. [ABSTRACT FROM AUTHOR]

The compound tetrakis(trimethylsilyl)silane Si[Si(CH 3 ) 3 ] 4 (TSi) has been studied at room temperature for pressures up to 21.5(1) GPa, using X-ray powder diffraction with synchrotron radiation. Three different phases are reported in the investigated pressure range. The c.c.p.-type structure is stable up to a pressure of 0.19(1) GPa ( $ \hbox{Fm}\bar{3}\hbox{m} $ , a = 13.5211(1) Å, V = 2471.95(1) Å 3 , Z = 4 at 0.02(1) GPa). It shows a severe orientational disorder of the molecules. At pressures 0.19(1)-0.71(1) GPa a monoclinic phase (HP1) is found with space group P 2 1 / n and Z = 8 ( a = 17.746(1) Å, b = 16.098(1) Å, c = 16.871(1) Å, γ = 111.437(5) and V = 4486.3(8) Å 3 at 0.24(1) GPa). Another monoclinic phase (HP2) exists at pressures 0.52(1)-8.67(5) GPa. This phase has a smaller unit cell than the HP1 phase with Z = 2 ( a = 8.3778(8) Å, b = 9.1050(7) Å, c = 13.3024(8) Å, γ = 111.63(1) and V = 943.22(6) Å 3 at 1.73(2) GPa). The pressure dependencies of the unit-cell volumes are successfully described by Murnaghan or Vinet-type equations of state. The structures at different pressures and temperatures of TSi and related compounds are described as distorted superstructures of the c.c.p. arrangement. The occurrence of different superstructures is rationalized as the result of an optimized packing of ordered molecules of various shapes. [ABSTRACT FROM AUTHOR]

Na3PO2S2 was synthesized from the corresponding undecahydrate by freeze–drying. It dismutates at temperatures above 350 °C into Na3PO3S and Na3POS3. The crystal structure of Na3PO2S2 was determined from X-ray powder diffraction data, and refined using the Rietveld technique (Pbca, a=17.5359(2) A˚, b=11.3044(1) A˚, c=5.8656(1) A˚, RF2=8.45%, Rp=4.80%, Rwp=6.79%). The baricenters of the PO2S2-tetrahedra are arranged in the sense of a hexagonal close packing. One of the P&z.sbnd;O bonds of these tetrahedra is oriented parallel to the crystallographic c-axis with the POS2-groups in an eclipsed mutual orientation. The crystal structure of Na3PO2S2 displays a close relationship to the ones of Ca3CrN3 and Na3POS3. Above 330 °C, Na3PO2S2 can be regarded as a fast ionic conductor (with σ>10−5 S cm−1). [Copyright &y& Elsevier]

Deals with a study which investigated the temperature dependence of the crystal structure of lead tetroxide using high-resolution angle-dispersive X-ray powder diffraction. Experimental methods; Results; Discussion.