Two polymorphs of afobazole from powder diffraction data

Afobazole {systematic name: 2‐[2‐(morpholin‐4‐yl)ethylsulfanyl]‐1H‐benzimidazole} is a new anxiolytic drug and Actins, Auzins & Petkune [(2012). Eur. Patent EP10163962] described four polymorphic modifications. In the present study, the crystal structures of two monoclinic polymorphs, 5‐ethoxy‐2‐[2‐(morpholin‐4‐ium‐4‐yl)ethylsulfanyl]‐1H‐benzimidazol‐3‐ium dichloride, C₁₅H₂₃N₃O₂S²⁺·2Cl⁻, (II) and (IV), have been established from laboratory powder diffraction data. The crystal packing and conformation of the dications in (II) and (IV) are different. In (II), there are channels in the [001] direction, which offer atmospheric water molecules an easy way of penetrating into the crystal structure, thus explaining the higher hygroscopicity of (II) compared with (IV).     

Differential evolution: crystal structure determination of a triclinic polymorph of adipamide from powder diffraction data

The crystal structure of a previously unknown triclinic polymorph of adipamide has been solved from laboratory X-ray powder diffraction data using a new direct space global optimisation method based on differential evolution.     

Quantification of flupirtine maleate polymorphs using X-ray powder diffraction

Flupirtine maleate,a pharmaceutical compound for treating psychotic disease in clinics,has seven polymorphs.Form A,with better crystal stability and bioavailability,has been widely used as the pharmaceutical crystal form.Unfortunately,it is usually found in a polymorphic mixture with form B.In this study,pure crystal forms of A and B were prepared and characterized by X-ray powder diffraction (XRPD),Fourier transform infrared spectroscopy (FT-IR) and thermal analysis.An XRPD-based method for the quantitative determination of the amount of the flupirtine maleate polymorphs form A and form B was also established through a systematic optimization of instrumental parameters.The results of the analytical methodology validation showed that the XPRD method had a broad quantitative range of 0-100%(w/w),good linear relationship,with R²=0.999,excellent repeatability and precision and low limits of detection (LoD) of 0.15%(w/w) and quantification (LoQ) of 0.5%(w/w).The results also showed that the single-peak method was not as good as the whole pattern in reducing the influence of the preferred orientation,but this can be compensated for by a systematic optimization of instrumental parameters and validating the analytical methodology to reduce errors and obtain a good,repeatable,sensitive,and accurate method.This XRPD method can be used to analyze mixtures of flupirtine maleate polymorphs (forms A and B) quantitatively and control the quality of the bulk drug.     

Ezetimibe anhydrate,determined from laboratory powder diffraction data

Ezetimibe {systematic name: (3R,4S)‐1‐(4‐fluorophenyl)‐3‐[(3S)‐3‐(4‐fluorophenyl)‐3‐hydroxypropyl]‐4‐(4‐hydroxyphenyl)azetidin‐2‐one}, C₂₄H₂₁F₂NO₃, is used to lower cholesterol levels by inhibiting cholesterol resorption in the human intestine. The crystal structure of ezetimibe anhydrate was solved from laboratory powder diffraction data by means of real‐space methods using the program DASH [David et al. (2006). J. Appl. Cryst. 39 , 910–915]. Subsequent Rietveld refinement with TOPAS Academic [Coelho (2007). TOPAS Academic User Manual. Version 4.1. Coelho Software, Brisbane, Australia] led to a final R_wp value of 8.19% at 1.75 Å resolution. The compound crystallizes in the space group P2₁2₁2₁ with one molecule in the asymmetric unit. The molecules are closely packed and two intermolecular hydrogen bonds form an extended hydrogen‐bond architecture.     

X-ray powder diffraction study of monoclinic V-ZrO2 solid solutions obtained from gels

Rietveld refinement of six monoclinic V_xZr_1−xO₂ solid solutions, with x=0, 0.01, 0.02, 0.05, 0.075 and 0.1, prepared by heating dried gel precursors at 1300°C in air atmosphere, has been characterized using X-ray powder diffractometer data. The present results confirm that crystal structure of these solid solutions contain V⁴⁺(Zr⁴⁺) cations surrounded by seven oxygens, four at a distance between 2.13 and 2.28 Å (referred as to O(2) in the tetrahedrally coordinated oxygens) and other three at a distance between 2.03 and 2.20 Å (denoted as O(1) in the triangularly coordinated oxygens). The trends in the lattice parameter variation of V_xZr_1−xO₂ solid solutions specimens with the nominal vanadium amount are in accordance with previous results obtained by experiments measured using an internal standard.     

Metergoline II: structure solution from powder diffraction data with preferred orientation and from microcrystal

Metergoline is a dopamine agonist and serotonin antagonist used both in human and veterinary medicine. In addition to the previously known crystalline form, a new polymorph, which crystallizes from aqueous solution, was found. Since it was initially impossible to prepare a single crystal of quality suitable for single crystal X-ray diffraction measurements using a conventional laboratory source, the structure was solved from the powder diffraction data using synchrotron radiation. The structure determination also included solving the effects of preferred orientation. Characterization was simultaneously done by solid-state NMR spectroscopy. Finally, a small single crystal suitable for synchrotron diffraction was found after numerous tries. Crystal structure determination using this single crystal confirmed the powder-based solution. Comparison of information obtained by different experimental methods (powder diffraction, ssNMR, single crystal diffraction) was made.     

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.     

Reassessment of paracetamol orthorhombic Form III and determination of a novel low‐temperature monoclinic Form III‐m from powder diffraction data

Paracetamol [N‐(4‐hydroxyphenyl)acetamide, C₈H₉NO₂] has several polymorphs, just like many other drugs. The most stable polymorphs, denoted Forms I and II, can be obtained easily and their crystal structures are known. Crystals of the orthorhombic, less stable, room‐temperature Form III are difficult to grow; they need a special recipe to crystallize and suffer from severe preferred orientation. A crystal structure model of Form III has been proposed and solved from a combination of structure prediction and powder X‐ray diffraction (PXRD) [Perrin et al. (2009). Chem. Commun. 22 , 3181–3183]. The final R_wp value of 0.138 and the corresponding considerable residual trace were reasons to check its validity. A new structure determination of Form III using new high‐resolution PXRD data led to a final R_wp value of 0.042 and an improvement of the earlier proposed model. In addition, a reversible phase transition was found at 170–220 K between the orthorhombic Form III and a novel monoclinic Form III‐m. The crystal structure of Form III‐m has been determined and refined from PXRD data to a final R_wp value of 0.059.     

X-ray powder diffraction data for nine analgesics

X-Ray powder diffraction data for nine analgesics have been obtained by using a powder diffractometer. The results obtained by using the McCreery and Bystr?m-Asklund methods of sample loading were averaged and tabulated in terms of the lattice spacings and the relative line intensities. Data from powder camera films were compared with the diffractometer data, and certain discrepancies in the intensities are discussed.     

Phosphorescence and ODMR studies of isotopically mixed monoclinic and triclinic 1,4-dichlorobenzene

Phosphorescence and optically detected magnetic resonance (ODMR) studies were performed on the perprotonated triplet traps in isotopically mixed (h₄ in d₄) 1,4-dichlorobenzene at 1.75 K. We find evidence for two distinct crystalline phases of the d₄ host crystal which are stable in temperature ranges near room temperature, each of which induces a distinct set of ODMR parameters on the trap species being monitored. Both cw and pulsed ODMR are used to probe for evidence of trap-to-trap triplet energy transfer at several trap concentrations. We find that at low concentrations ODMR signals are strong, and the excitations are definitely localized. At concentrations above 9%, both coherent and cw ODMR signals become hard to detect. The results are discussed in terms of likely mechanisms for energy exchange among the triplet traps.     

The structure of azomethine block copolymers from X-ray powder diffraction data

The crystal structure of a block copolymer, constituted by the periodic alternation of three thienyl- and two phenyl fragments separated by azomethine residues, has been determined and refined on powder X-ray diffraction data. Polymers of this kind are particularly interesting because of some evidences of electronic confinement, i. e. possible realization of multiple-quantum-dot sequences have been detected. Although the quality of the measured profile was poor, a molecular model is proposed giving a satisfactory agreement with the observed data.     

Crystal structure determination of AlVMoO7 from X-ray powder diffraction data

The structure of AlVMoO₇ was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)Å, b=8.1644(3)Å and c=12.7312Å. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO₅ pyramids are edge linked to infinite (VO₂⁺)_∞ chains. Therefore, AlVMoO₇ can be classified as a polyvanadate.     

trans‐Decahydronaphthalene (decalin) from powder diffraction data

The title compound, C₁₀H₁₈, a decalin stereoisomer, crystallizes with Z′ = 0.5 in the space group P2₁/n. The trans‐decalin molecule is located on an inversion centre with both rings in a chair conformation, making for a quasi‐flat overall shape. Despite the absence of hydrogen bonds, it crystallizes easily. In this work the unknown crystal structure of trans‐decalin has been solved and refined using X‐ray powder diffraction data.     

The crystal structure of 3-methyluracil from X-ray powder diffraction data

The crystal structure of 3-methyluracil has been determined ab initio by conventional monochromatic X-ray powder diffraction data. The crystal data are: orthorombic, a=6.6294(1), b=13.1816(3), c=6.53938(9) (Å), V=571.45(3) (ų), space group Pbnm, Z=8. The structure was solved by direct methods and the final Rietveld refinement converged to R_p=0.0398, R_wp=0.0528, R_Bragg=0.0294. The crystal structure exhibits endless chains of planar molecules, connected via head-to-tail N-H?O hydrogen bonds.     

Structure determination from powder diffraction

The review surveys modern methods for the determination of unknown crystal structures of organic and inorganic compounds from powder diffraction data. The main stages of this process, from the preparation of the specimen to a search for the structural motif followed by the Rietveld refinement, are considered. The results obtained on different diffractometers using X-ray, synchrotron, and neutron radiations are demonstrated to be well reproducible. Examples of successful structure solution are cited, which provide evidence that powder diffraction is a reliable tool in establishing structures of a wide range of compounds for which single crystals are unavailable.     

On pattern matching of X-ray powder diffraction data

We introduce a novel pattern matching algorithm optimized for X-ray powder diffraction (XRPD) data and useful for data from other types of analytical techniques (e.g., Raman, IR). The algorithm is based on hierarchical clustering with a similarity metric that compares peak positions using the full peak profile. It includes heuristics developed from years of experience manually matching XRPD data, and preprocessing algorithms that reduce the effects of common problems associated with XRPD (e.g., preferred orientation and poor particle statistics). This algorithm can find immediate application in automated polymorph screening and salt selection, common tasks in the development of pharmaceuticals.     

Isoscalar factors for tetragonal,orthorhombic, monoclinic and triclinic shubnikov point groups

The relations between isoscalar factors for corepresentations of antiunitary magnetic point groups are discussed in the case of associated corepresentations. The tables of the isoscalar factors for the single- and double-valued corepresentations of all tetragonal, orthorhombic, monoclinic, and triclinic Shubnikov point groups are given. Some peculiarities of the calculation method of the isoscalar factors for corepresentations are considered.     

Structural analysis of a melaminium polyphosphate from X-ray powder diffraction and solid-state NMR data

The crystal structure of the environmentally friendly flame retardant melaminium polyphosphate (MPoly) (2,4,6-triamino-1,3,5-triazinium x PO(3))(n)was determined by a direct-space global optimization technique from X-ray powder diffraction data. Solid-state NMR was used to corroborate the proposed hydrogen-bonding model and to determine the average degree of polymerization (n > 100). An analysis of the crystal structure of MPoly reveals aspects of molecular geometry and packing that are characteristic for melamine-containing compounds and polyphosphate salts. A comparison of MPoly with the crystal structures of its precursors melaminium orthophosphate (MP) and melaminium dihydrogenpyrophosphate (MPy) provides insight in the mechanism of the endothermic dehydration processes that takes place in the reaction path MP --> MPy --> MPoly. Solid-state NMR characterization of various samples of the same batch showed inhomogeneities in the MPoly composition. Various quantities of orthophosphates were found, which cannot be assigned to be MP.