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X-ray powder diffraction, CRYSTAL structure, SCHIFF bases, RIETVELD refinement, and NICKEL

The crystal structures of the azomethine nickel complexes Pigment Orange 68 (P.O.68, C29H18N4O3Ni), Pigment Red 257 (P.R.257, C16H4Cl8N6O2Ni), and Solvent Brown 53 (S.Br.53, C18H10N4O2Ni) were determined from powder diffraction data. The compounds are industrially used for the colouration of plastics and coatings. P.O.68 exists in two polymorphic forms, the commercial one is the α-phase. The crystal structures were solved from laboratory data using real-space methods and refined by the Rietveld method. For the Rietveld refinement of α-P.O.68, synchrotron data were employed. In all structures, the Ni2+ ion is coordinated by two N atoms and two O atoms in a square-planar geometry. Both phases of P.O.68 crystallise in P21/c, Z = 4. In both structures, the molecules form dimers via an inversion centre, with Ni-to-Ni distances of 3.606 Å (α-phase) and 3.286 Å (β-phase). The dimers are stacked into columns. Neighbouring columns are connected by hydrogen bonds: one classical N–H⋅⋅⋅O bond, and one N–H⋅⋅⋅π bond to the naphthalene moiety of a molecule in the neighbouring stack. P.R.257 crystallises in P21/c, Z = 2, with molecules on inversion centres. The molecules show a typical van der Waals packing without close Ni-Ni contacts. S.Br.53 exhibits Pbcn symmetry with Z = 8. The molecules form columns with Ni-to-Ni distances of 3.508 Å. [ABSTRACT FROM AUTHOR]

Pharmacology drugs, Pharmacologie, galénique, Sciences biologiques et medicales, Biological and medical sciences, Sciences medicales, Medical sciences, Pharmacologie. Traitements medicamenteux, Pharmacology. Drug treatments, Pharmacologie générale, General pharmacology, Technologie pharmaceutique. Industrie pharmaceutique, Pharmaceutical technology. Pharmaceutical industry, Benzothiazine dérivé, Benzothiazine derivatives, Benzotiazina derivado, Dérivé de l'oxicam, Oxicam derivatives, Oxicam derivado, Enzyme, Enzima, Inhibiteur enzyme, Enzyme inhibitor, Inhibidor enzima, Oxidoreductases, Prostaglandin-endoperoxide synthase, Analgésique, Analgesic, Analgésico, Antiinflammatoire non stéroïde, Non steroidal antiinflammatory agent, Antiinflamatorio no esteroide, Antipyrétique, Antipyretic, Antipirético, Criblage, Screening, Cernido, Diffraction RX, X ray diffraction, Difracción RX, Diffractométrie RX, X ray diffractometry, Difractometría RX, Modèle moléculaire, Molecular model, Modelo molecular, Piroxicam, Polymorphisme, Polymorphism, Polimorfismo, Poudre, Powder, Polvo, Séchage pulvérisation, Spray drying, Secado pulverización, Technologie pharmaceutique, Pharmaceutical technology, Tecnología farmacéutica, Analyse à haut débit, X-ray diffractometry, X-ray powder diffraction, crystallography, molecular modelling, piroxicam, polymorph screening, polymorphism, and spray drying

High-throughput crystallisation and characterisation platforms provide an efficient means to carry out solid-form screening during the pre-formulation phase. To determine the crystal structures of identified new solid phases, however, usually requires independent crystallisation trials to produce single crystals or bulk samples of sufficient quantity to carry out high-quality X-ray diffraction measurements. This process could be made more efficient by a robust procedure for crystal structure determination directly from high-throughput X-ray powder diffraction (XRPD) data. Quantum―chemical calculations based on dispersion-corrected density functional theory (DFT-D) have now become feasible for typical small organic molecules used as active pharmaceutical ingredients. We demonstrate how these calculations can be applied to complement high-throughput XRPD data by determining the crystal structure of piroxicam form III. These combined experimental/quantum―chemical methods can provide access to reliable structural information in the course of an intensive experimentally based solid-form screening activity or in other circumstances wherein single crystals might never be viable, for example, for polymorphs obtained only during high-energy processing such as spray drying or milling.