Two forms of aluminium phosphate tridymite from X‐ray powder data

Monoclinic and triclinic (pseudo‐orthorhombic) AlPO₄ tridymites have been refined from X‐ray powder diffraction data using the silica analogues as starting models. The framework structures of both forms of tridymite are made up of six‐membered rings of tetrahedra which differ in the distortion patterns of the ring shapes. Ordered occupation of alternate tetrahedra by Al and P leads to a doubling of the a lattice parameter for monoclinic AlPO₄ tridymite (space group Pc) and loss of the C‐centring with respect to the isotypic silica tridymite (space group Cc). Triclinic AlPO₄ tridymite was refined in the same space group (F1) as the SiO₂ analogue.     

Hexagonal high‐temperature form of aluminium phosphate tridymite from X‐ray powder data

Similar to silica tridymite, AlPO₄ tridymite shows a sequence of displacive phase transitions resulting in a dynamically disordered hexagonal high‐temperature modification. Rietveld refinement reveals that the thermal motions of the tetrahedra can be described either by strongly anisotropic displacement parameters for oxy­gen or by split O atoms. Due to the ordered distribution of aluminium and phospho­rus over alternating tetrahedra, the space group symmetry of high‐temperature AlPO₄ tridymite is reduced with respect to SiO₂ tridymite from P6₃/mmc to P6₃mc.     

K3TaF8 from laboratory X‐ray powder data

The crystal structure of tripotassium octafluoridotantalate, K₃TaF₈, determined from laboratory powder diffraction data by the simulated annealing method and refined by total energy minimization in the solid state, is built from discrete potassium cations, fluoride anions and monocapped trigonal–prismatic [TaF₇]²⁻ ions. All six atoms in the asymmetric unit are in special positions of the P6₃mc space group: the Ta and one F atom in the 2b (3m) sites, the K and two F atoms in the 6c (m) sites, and one F atom in the 2a (3m) site. The structure consists of face‐sharing K₆ octahedra with a fluoride anion at the center of each octahedron, forming chains of composition [FK₃]²⁺ running along [001] with isolated [TaF₇]²⁻ trigonal prisms in between. The structure of the title compound is different from the reported structure of Na₃TaF₈ and represents a new structure type.     

Lead tartrate from X‐ray powder diffraction data

The structure of lead tartrate, Pb²⁺·C₄H₄O₆^2?, has been solved from X‐ray powder diffraction data. The cation exhibits ninefold coordination and the tartrate groups are linked through Pb?O contacts to form a three‐dimensional network.     

Ca2MgWO6 from neutron and X‐ray powder data

The room‐temperature structure of the B‐site‐ordered complex perovskite dicalcium magnesium tungstate, Ca₂MgWO₆, has been determined by simultaneous Rietveld refinement of neutron and X‐ray powder diffraction patterns. Ca₂MgWO₆ is characterized by B‐site ordering and an a⁻a⁻c⁺‐type BO₆ octahedral tilt mechanism.     

Lanthanum indium oxide from X‐ray powder diffraction

LaInO₃, a promising ion conductor for a holistic solid oxide fuel cell, was synthesized by a solid‐state reaction method. The structure was refined by the Rietveld method using X‐ray powder diffraction data. The structure of LaInO₃ is distorted by the in‐phase and antiphase tilting of oxy­gen octahedra in the a⁺b⁻b⁻ system of the InO₆ polyhedra. In the Pmna space group, the In atom lies on an inversion centre and the La atom and one of the O atoms lie on a mirror plane.     

1,4‐Bis[2‐(4‐ferrocenylphenyl)ethynyl]anthraquinone from synchrotron X‐ray powder diffraction

The title compound, [Fe₂(C₅H₅)₂(C₄₀H₂₂O₂)] or 1,4‐(FcPh)₂Aq [where FcPh is 2‐(4‐ferrocenylphenyl)ethynyl and Aq is anthraquinone], was synthesized in an attempt to obtain a new solvent‐incorporating porous material with a large void space. Thermodynamic data for 1,4‐(FcPh)₂Aq show a phase transition at approximately 430 K. The crystal structure of solvent‐free 1,4‐(FcPh)₂Aq was determined at temperatures of 90, 300 and 500 K using synchrotron powder diffraction data. A direct‐space method using a genetic algorithm was employed for structure solution. Charge densities calculated from observed structure factors by the maximum entropy method were employed for model improvement. The final models were obtained through multistage Rietveld refinements. In both phases, the structures of which differ only subtly, the planar Aq fragments are stacked alternately in opposite orientations, forming a one‐dimensional column. The FcPh arms lie between the stacks and fill the remaining space, leaving no voids. C—H...π interactions between the Ph and Fc fragments mediate crystal packing and stabilization.     

Magnesium perchlorate anhydrate,Mg(ClO4)2, from laboratory X‐ray powder data

The previously unknown crystal structure of magnesium perchlorate anhydrate, determined and refined from laboratory X‐ray powder diffraction data, represents a new structure type. The title compound was obtained by heating magnesium perchlorate hexahydrate at 523 K for 2 h under vacuum and it crystallizes in the monoclinic space group P2₁/c. The asymmetric unit contains one Mg (site symmetry on special position 2a), one Cl and four O sites (on general positions 4e). The structure consists of a three‐dimensional network resulting from the corner‐sharing of MgO₆ octahedra and ClO₄ tetrahedra. Each MgO₆ octahedron share corners with six ClO₄ tetrahedra. Each ClO₄ tetrahedron shares corners with three MgO₆ octahedra, with one O‐atom corner dangling. The ClO₄ tetrahedra are oriented in such a way that one‐dimensional channels parallel to [100] are formed between the dangling O atoms.     

2,4‐Dimethyl‐1,3‐thiazole‐5‐carboxylic acid: an X‐ray structural study at 100 K and Hirshfeld surface analysis

The crystal structure of the title thiazolecarboxylic acid derivative, C₆H₇NO₂S, (I), has been determined from single‐crystal X‐ray analysis at 100 K. In the crystal packing, an interplay of O—H...N and C—H...O hydrogen bonds connects the molecules to form C(6)R₂²(8) polymeric chains, which are further linked via weak C—H...O hydrogen bonds into a two‐dimensional supramolecular framework. The relative contributions of different interactions to the Hirshfeld surface in (I) and a few related thiazolecarboxylic acid derivatives indicate that the H...H, N...H and O...H contacts can account for about 50–70% of the total Hirshfeld surface area in this class of compound.     

4‐Ethynyl‐1,2‐methylenedioxybenzene at 150 K

The title compound, C₉H₆O₂, contains two moderate C—H?O hydrogen bonds. That involving the terminal alkyne gives rise to chains along the b axis. The other hydrogen bond occurs over a centre of symmetry, leading to dimers. The combination of the two interactions gives rise to rings, each comprising six mol­ecules, which are part of infinite sheets in the bc plane.     

Single‐Crystal X‐ray Diffraction Structure of the Stable Enol Tautomer Polymorph of Barbituric Acid at 224 and 95 K

The thermodynamically stable enol crystal form of barbituric acid, previously prepared as powder by grinding or slurry methods, has been obtained as single crystals by slow cooling from methanol solution. The selection of the enol crystal was facilitated by a density‐gradient method. The structure at 224 and 95 K confirms the enol inferred on the basis of powder data. The enol has bond lengths that are consistent with the expected bond order and with DFT calculations that include treatment of hydrogen bonding. In isolation, the enol is higher in energy than the tri‐keto form by 50 kJ mol^?1 which must be more than compensated by enhanced hydrogen bonding. Both crystal forms have four normal H‐bonds; the enol has two additional H‐bonds with O–O distances of 2.49 Å. Conversion into the enol form occurs spontaneously in the solid state upon prolonged storage of the commercial tri‐keto material. Slurry conversion of tri‐one to enol in ethanol is reversed in direction in ethanol‐D₁.     

Substituent effects in trans‐p,p′‐disubstituted azobenzenes: X‐ray structures at 100 K and DFT‐calculated structures

The crystal and molecular structures of two para‐substituted azobenzenes with π‐electron‐donating –NEt₂ and π‐electron‐withdrawing –COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the –NEt₂ group in N,N,N′,N′‐tetraethyl‐4,4′‐(diazenediyl)dianiline, C₂₀H₂₈N₄, (I), may be caused by steric hindrance and the π‐electron‐donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clear sp²‐hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4′‐(diazenediyl)dibenzoate, C₁₈H₁₈N₂O₄, (II), lies on a crystallographic inversion centre. Its geometry is normal and comparable with homologous compounds. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecules. The most significant changes are observed in the values of the N=N—C—C torsion angles, which for the isolated molecules are close to 0.0°. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates a slight decrease of the aromaticity in (I) and no substantial changes in (II).     

Reinterpretation of the monohydrate of clarithromycin from X‐ray powder diffraction data as a trihydrate

Noguchi, Fujiki, Iwao, Miura & Itai [Acta Cryst. (2012), E 68 , o667–o668] recently reported the crystal structure of clarithromycin monohydrate from synchrotron X‐ray powder diffraction data. Voids in the crystal structure suggested the possible presence of two more water molecules. After successful location of the two additional water molecules, the Rietveld refinement still showed minor problems. These were resolved by noticing that one of the chiral centres in the molecule had been inverted. The corrected crystal structure of clarithromycin trihydrate, refined against the original data, is now reported. Dispersion‐corrected density functional theory calculations were used to check the final crystal structure and to position the H atoms.     

Na2Fe(CN)5(NO)·2D2O at 11 and 293 K by X‐ray,and at 15 K by neutron diffraction

The crystal structure of Na₂Fe(CN)₅(NO)·2D₂O, disodium penta­cyano­nitro­syl­ferrate(III) bis­(dideuterium oxide), has been determined by X‐ray diffraction at 11 and 293 K, and by neutron diffraction at 15 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters between the determinations at low temperature is very good.     

Acetone‐4‐methyl­thio­semicarbazone at 220 K

In the title compound, C₅H₁₁N₃S, the trans conformation is stabilized by a weak intramolecular N—H?N hydrogen bond. Unusually, one N—H bond is not involved in any hydrogen‐bond interactions and instead the mol­ecules form a one‐dimensional polymer via N—H?S intermolecular hydrogen bonds.     

[Pd(CH3COO)2]n from X‐ray powder diffraction data

The water‐insoluble title compound, catena‐poly­[palladium(II)‐di‐μ‐acetato‐κ⁴O:O′], [Pd(C₂H₃O₂)₂]_n, was obtained from a nitratopalladium solution and acetic acid as a pale‐pink powder. Ab initio crystal structure determination was carried out using X‐ray powder diffraction techniques. Patterson and Fourier syntheses were used for atom location and the Rietveld technique was applied for the final structure refinement. The structure consists of palladium acetate complexes connected into polymeric chains running along b, in which two Pd atoms are bridged by two acetate groups that are in a cis configuration with respect to one another. The unique Pd atom lies on a site with 2/m symmetry and the acetate moieties have imposed m symmetry; these are joined into infinite chains running along the b direction. The shortest Pd⋯Pd distance in the row is 2.9192 (1) Å. The planes of adjacent palladium complexes are inclined towards each other, the angle between the planes being approximately 30°.     

Two polymorphs of anhydrous 4‐pyridone at 100 K

Two polymorphs of the title compound, C₅H₅NO, (I), have been obtained from ethanol. One polymorph crystallizes in the monoclinic space group C2/c [henceforth (I)‐M], while the other crystallizes in the orthorhombic space group Pbca [henceforth (I)‐O]. In the two forms, the lattice parameters, cell volume and packing motifs are very similar. There are also two independent molecules of 4‐pyridone in each asymmetric unit. The molecules are linked by N—H...O hydrogen bonds into one‐dimensional zigzag chains extending along the b axis in the (I)‐M polymorph and along the a axis in the (I)‐O polymorph, with the graph set C₂²(12). The structures are stabilized by weak C—H...O hydrogen bonds linking adjacent chains, thus forming a ring with the graph set R₆⁵(28). The significance of this study lies in the analysis of the hydrogen‐bond interactions occurring in these structures. Analyses of the crystal structures of the two polymorphs of 4‐pyridone are helpful in elucidating the mechanism of the generation of spectroscopic effects observed in the IR spectra of these polymorphs in the frequency range of the N—H stretching vibration band.     

γ‐Sodium gallate: a Rietveld refinement using X‐ray powder diffraction

Tetrahedrally coordinated oxides usually present polymorphism, but for NaGaO₂, only the β polymorph has been reported. In this work, the synthesis and structural characterization of γ‐sodium gallate, γ‐NaGaO₂, are presented. The crystal structure belongs to the orthorhombic system, space group Pbca (No. 61), and has been characterized by a Rietveld refinement of the X‐ray powder diffraction pattern. The structure is similar to those exhibited by the γ phases of many tetrahedral oxides.     

Herringbone array of hydrogen‐bonded ribbons in 2‐ethoxybenzamide from high‐resolution X‐ray powder diffraction

In 2‐ethoxybenzamide, C₉H₁₁NO₂, the amide substituents are linked into centrosymmetric head‐to‐head hydrogen‐bonded dimers. Additional hydrogen bonds between adjacent dimers give rise to ribbon‐like packing motifs, which extend along the c axis and possess a third dimension caused by twisting of the 2‐ethoxyphenyl substituent with respect to the hydrogen‐bonded amide groups. The ribbons are arranged in a T‐shaped herringbone pattern and cohesion between them is achieved by van der Waals forces.     

Disordered structure of ZrW1.8V0.2O7.9 from a combined X‐ray and neutron powder diffraction study at 530 K

A novel compound, vanadium aliovalent substituted zirconium tungstate, ZrW_1.8V_0.2O_7.9, was prepared with vanadium substituting tungsten rather than the common zirconium substitution. The structure of the high‐temperature phase was refined from combined neutron and X‐ray powder diffraction data gathered at 530 K. This phase is the disordered centric modification (space group Pa) and the average crystal structure is similar to that of β‐ZrW₂O₈. The V atom occupies only a W2 site and charge compensation is achieved through oxygen vacancy, i.e. the oxygen vacancy occurs at only the O4 site. [Atom names follow the established scheme; Evans et al. (1996). Chem. Mater. 8 , 2809–2823.]