Polymorphic transition due to grinding: the case of 3-[1-(tert-butoxycarbonyl)azetidin-3-yl]-1,2-oxazole-4-carboxylic acid.

A polymorphic transition as a result of grinding was found for 3-[1-(tert-butoxycarbonyl)azetidin-3-yl]-1,2-oxazole-4-carboxylic acid. The thorough study of polymorphic structures before and after crystal structure transformation has revealed some pre-conditions for a polymorphic transition and regularities of changes in molecular and crystal structure. In metastable polymorph 1a, the conformationally flexible molecule adopts a conformation with the higher energy and forms a less preferable linear supramolecular synthon. Additional energy imparted to a crystal structure during the grinding process proved to be enough to overcome low energy barriers for the nitrogen inversion and rotation of the oxazole ring around the sp3-sp2 single bond. As a result, polymorph 1b with a molecule adopting conformation with lower energy and forming a more preferable centrosymmetric supramolecular synthon was obtained. The study of pairwise interaction energies in the two polymorphs has shown that metastable polymorph 1a is organized by molecular building units and has a columnar-layered structure. A centrosymmetric dimer should be recognized as a complex building unit in more stable polymorph 1b, which has a layered structure.

1-Allyl-4-hydroxy-2,2-dioxo-N-(4-methoxyphenyl)-1H-2λ6,1-benzothiazine-3-carboxamide: polymorphic transition due to grinding with the loss of the biological activity.

A study of two polymorphic forms of 1-allyl-4-hydroxy-2,2-dioxo-N-(4-methoxyphenyl)-1-2λ6,1-benzothiazine-3-carboxamide (a structural analogue of piroxicam) has revealed some regularities in the crystal structure formation due to different evaporation rates from the tested solvents. The monoclinic polymorph crystallized from ethyl acetate is formed due to a large number of very weak C-H...O and C-H...π interactions as well as one strong stacking interaction. The triclinic polymorph crystallized from N,N-dimethylformamide is formed due to a small number of weak specific interactions and a maximal number of strong stacking interactions. The stacked dimer is a complex building unit in both polymorphic structures. Further analysis showed that the monoclinic structure is layered while the triclinic one is columnar. The two polymorphic structures also differ in their biological activity (antidiuretic and analgesic). The monoclinic polymorph possesses very high biological activity while the triclinic polymorph is almost inactive. The polymorphic transition of the biologically active metastable monoclinic structure into the inactive stable triclinic one within four weeks of grinding is caused by orientational factors rather than conformational ones and is accompanied by a change in the redistribution of interaction energies in the crystal from anisotropic to more isotropic. Thus, a slow polymorphic transition after grinding results in a loss of the biological activity.

Structural features of the oxidonitridophosphates K3 M III(PO3)3N (M III = Al, Ga).

Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K3 M III(PO3)3N (M III = Al, Ga), were grown by application of the self-flux method. In their isostructural crystal structures, all metal cations and the N atom occupy special positions with site symmetry 3, while the P and O atoms are situated in general positions. The three-dimensional framework of these oxidonitridophosphates is built up from [M IIIO6] octa-hedra linked together via (PO3)3N groups. The latter are formed from three PO3N tetra-hedra sharing a common N atom. The coordination environments of the three potassium cations are represented by two types of polyhedra, viz. KO9 for one and KO9N for the other two cations. An unusual tetra-dentate type of coordination for the latter potassium cations by the (PO3)3N6- anion is observed. These K3 M III(PO3)3N (M III = Al, Ga) compounds are isostructural with the Na3 M III(PO3)3N (M III = Al, V, Ti) compounds.

Mixed-metal phosphates K1.64Na0.36TiFe(PO4)3 and K0.97Na1.03Ti1.26Fe0.74(PO4)3 with a langbeinite framework.

Single crystals of the langbeinite-type phosphates K1.65Na0.35TiFe(PO4)3 and K0.97Na1.03Ti1.26Fe0.74(PO4)3 were grown by crystallization from high-temperature self-fluxes in the system Na2O-K2O-P2O5-TiO2-Fe2O3 using fixed molar ratios of (Na+K):P = 1.0, Ti:P = 0.20 and Na:K = 1.0 or 2.0 over the temperature range 1273-953 K. The three-dimensional framework of the two isotypic phosphates are built up from [(Ti/Fe)2(PO4)3] structure units containing two mixed [(Ti/Fe)O6] octa-hedra (site symmetry 3) connected via three bridging PO4 tetra-hedra. The potassium and sodium cations share two different sites in the structure that are located in the cavities of the framework. One of these sites has nine and the other twelve surrounding O atoms.

Usage of Quantum Chemical Methods to Understand the Formation of Concomitant Polymorphs of Acetyl 2-(N-(2-Fluorophenyl)imino)coumarin-3-carboxamide.

Crystallization of concomitant polymorphs is a very intriguing process that is difficult to be studied experimentally. A comprehensive study of two polymorphic modifications of acetyl 2-(N-(2-fluorophenyl)imino)coumarin-3-carboxamide using quantum chemical methods has revealed molecular and crystal structure dependence on crystallization conditions. Fast crystallization associated with a kinetically controlled process results in the formation of a columnar structure with a nonequilibrium molecular conformation and more isotropic topology of interaction energies between molecules. Slow crystallization may be considered as a thermodynamically controlled process and leads to the formation of a layered crystal structure with the conformation of the molecule corresponding to local minima and anisotropic topology of interaction energies. Fast crystallization results in the formation of a lot of weak intermolecular interactions, while slow crystallization leads to the formation of small amounts of stronger interactions.

Scheelite-related MBi1-xV1-xMoxO4 (MII- Ca, Sr) solid solution-based photoanodes for enhanced photoelectrochemical water oxidation.

The photoelectrochemical properties of scheelite-related MBi1-xV1-xMoxO4 (MII = Ca, Sr, x = 0.1 to 0.9) solid solutions deposited on conductive glass (coated with SnO2, F-doped) have been investigated as photoanodes in photoelectrochemical (PEC) water splitting. The variation of the final annealing temperature during the preparation of the conduction electrodes as well as the value of substitution x have been shown to affect the PEC performance. The micropowders of MBi1-xV1-xMoxO4 (MII = Ca, Sr, x = 0.1 to 0.9) samples were first fabricated vi a solid-state method; they were characterised by SEM microscopy and powder and single crystal X-ray diffraction, and the band gap values were estimated using diffusive reflectance data. The value of substitution x = 0.1 in the cases of samples containing calcium and strontium affords the highest PEC performance reported for the whole range of substitution. These results demonstrate a promising approach for the beneficial utilization of BiVO4-substituted scheelite-related solid solutions in photo-electrochemical cells towards efficient and inexpensive photoanodes.

Synthesis, Crystal Structure, and Biological Activity of Ethyl 4-Methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate Polymorphic Forms.

Continuing the search for new potential analgesics among the derivatives of 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylic acid, the possibility of obtaining its esters by the alkylation of the corresponding sodium salt with iodoethane in dimethyl sulfoxide (DMSO) at room temperature was studied. It was found that under such conditions, together with the oxygen atom of the carboxyl group, a heteroatom of nitrogen is also alkylated. Therefore, the product of the reaction studied is a mixture of ethyl 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate (major) and its 1-ethyl-substituted analog (minor). A simple but very effective method of preparative separation of these compounds was proposed. Moreover, the heterogeneous crystallization from ethanol was revealed to result in a monoclinic polymorphic form of ethyl 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate, while the homogeneous crystallization results in its orthorhombic form. The molecular and crystal structures of both forms were confirmed by X-ray diffraction analysis, and the phase purity by powder diffraction study. The pharmacological tests carried out on the model of a carrageenan edema showed that the screening dose of 20 mg/kg of 1-ethyl-substituted ester and the orthorhombic form of its analog unsubstituted in position 1 exhibited weak anti-inflammatory and moderate analgesic effects. At the same time, the monoclinic form of ethyl 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate appeared to be both a powerful analgesic and an anti-inflammatory agent that exceeded Piroxicam and Meloxicam in the same doses by these indicators. A detailed comparative analysis of the molecular and crystal structures of two polymorphic forms of ethyl 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate was carried out using quantum chemical calculations of the energies of pairwise interactions between molecules. An explanation of the essential differences of their biological properties based on this was offered.

New complex phosphates Cs3MIIBi(P2O7)2 (MII - Ca, Sr and Pb): synthesis, characterization, crystal and electronic structure.

Herein, the peculiarities of complex phosphate formation in self-fluxes of Cs-MII-Bi-P-O (MII = Ca, Sr, Ba and Pb) systems with Cs/P = 0.7-1.3 at fixed ratios of Bi/P = 0.2 and Bi/MII = 1.0 were studied and discussed. Three novel isostructural diphosphates with the general composition Cs3MIIBi(P2O7)2 (MII = Ca, Sr and Pb) and the original framework topology were synthesized and characterized via single-crystal and powder X-ray diffraction, SEM, DTA, and FTIR- and UV-VIS-spectroscopy. In addition, electronic structure (DFT) and Voronoi-Dirichlet polyhedra (VDP) characteristics calculations and crystallochemical analysis were performed. In the structure of the new compounds, the MIIO7 and BiO6 polyhedra are connected via common oxygen vertices forming infinite helical-like chains, which are linked by P2O7 groups into a 3D-framework with pentagonal tunnels, where the Cs+ cations are located. The structural peculiarities are discussed considering perspectives for the creation of new luminescent materials. The dielectric bandgaps, Eg, of the Cs3MIIBi(P2O7)2 crystals reveal an ∼0.2 eV low-energy shift in the Ca-Sr-Pb sequence of MII cations, which reveals the possibility to tune the optical absorbance spectra of the crystals via the synthesis of solid solutions with various contents of MII cations. The glass-ceramic synthetic approach is also proposed as a convenient method for the creation of new diphosphates, and the applicability of this method is verified for Cs3CaBi(P2O7)2.

Novel modification of anhydrous transition metal oxalates from powder diffraction.

The known metal-C2O4 structures may be divided into two modifications, α and ß. The α-modification has an order-disorder struxture, revealing one-dimensional disordering of the metal-oxalate chains, and the ß-modification is ordered. The crystal structures of orthorhombic γ-MnC2O4 {poly[µ-oxalato-manganese(II)]; space group Pmna, a = 7.1333 (1), b = 5.8787 (1), c = 9.0186 (2) Å, V = 378.19 (1) Å3, Z = 4 and Dx = 2.511 Mg m-3} and γ-CdC2O4 {poly[µ-oxalato-cadmium(II)]; space group Pmna, a = 7.3218 (1), b = 6.0231 (1), c = 9.2546 (2) Å, V = 408.13 (1) Å3, Z = 4 and Dx = 3.262 Mg m-3} have been obtained from powder diffraction patterns. The structures are isostructural. Each metal atom in each structure is coordinated by seven O atoms which belong to five oxalate ions. The crystal packing, which contains noticeable cavities in the [101] and [001] directions, is not close packed and essentially differs from the known disordered α- and ordered ß-modifications of transition metal oxalates. This modification seems to be metastable. It was found that a spontaneous Î³â†’ß phase transition takes place for γ-CdC2O4.

Two pseudo-enantiomeric forms of N-benzyl-4-hydroxy-1-methyl-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxamide and their analgesic properties.

The fact that molecular crystals exist as different polymorphic modifications and the identification of as many polymorphs as possible are important considerations for the pharmaceutic industry. The molecule of N-benzyl-4-hydroxy-1-methyl-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxamide, C17H16N2O4S, does not contain a stereogenic atom, but intramolecular hydrogen-bonding interactions engender enantiomeric chiral conformations as a labile racemic mixture. The title compound crystallized in a solvent-dependent single chiral conformation within one of two conformationally polymorphic P212121 orthorhombic chiral crystals (denoted forms A and B). Each of these pseudo-enantiomorphic crystals contains one of two pseudo-enantiomeric diastereomers. Form A was obtained from methylene chloride and form B can be crystallized from N,N-dimethylformamide, ethanol, ethyl acetate or xylene. Pharmacological studies with solid-particulate suspensions have shown that crystalline form A exhibits an almost fourfold higher antinociceptive activity compared to form B.

Structural transformation of Bi1-x/3V1-xMoxO4 solid solutions for light-driven water oxidation.

The influence of molybdenum content in the solid solutions of Bi1-x/3V1-xMoxO4 (x = 0.05-0.20) on the morphology, band gap, structure and light-driven water oxidation properties has been studied by scanning electron microscopy, X-ray powder diffraction and vibrational spectroscopy (Raman and infrared). To find out the peculiarities of structural changes for bismuth scheelite-related oxides containing both vanadium and molybdenum crystals of Bi0.98V0.93Mo0.07O4 have been grown from a K-Bi-V-Mo-O high-temperature melt and characterized by single crystal X-ray diffraction. For the scheelite-related framework both V and Mo were found to occupy the same positions lowering the point group symmetry of tetrahedra from 4/m to 2/m giving monoclinic distortion for solid solutions with x = 0.05-0.10. The most promising photocatalytic performance was obtained for Bi0.96Mo0.10V0.90O4, in which the oxygen evolution could reach 21 µM in 50 s under visible light of LEDs, λ = 470 ± 10 nm, and 820 µE cm(-2) s(-1). The changes in catalytic properties are shown to be governed by a crystal structure strain with a maximum obtained for the boundary sample between the monoclinic and tetragonal phase.

Crystal structure of langbeinite-related Rb0.743K0.845Co0.293Ti1.707(PO4)3.

Potassium rubidium cobalt(II)/titanium(IV) tris-(orthophosphate), Rb0.743K0.845Co0.293Ti1.707(PO4)3, has been obtained using a high-temperature crystallization method. The obtained compound has a langbeinite-type structure. The three-dimensional framework is built up from mixed-occupied (Co/Ti(IV))O6 octa-hedra (point group symmetry .3.) and PO4 tetra-hedra. The K(+) and Rb(+) cations are statistically distributed over two distinct sites (both with site symmetry .3.) in the large cavities of the framework. They are surrounded by 12 O atoms.

The solid solution K3.84Ni0.78Fe3.19(PO4)5.

The title compound, tetra-potassium tetra-[nickel(II)/iron(III)] penta-kis-(orthophosphate), K3.84Ni0.78Fe3.19(PO4)5, has been obtained from a flux. The structure is isotypic with that of K4MgFe3(PO4)5. The three-dimensional framework is built up from (Ni/Fe)O5 trigonal bipyramids with a mixed Fe:Ni occupancy of 0.799 (8):0.196 (10) and isolated PO4 tetra-hedra, one of which is on a general position and one of which has -4.. site symmetry. Two K(+) cations are statistically occupied and are distributed over two positions in hexa-gonally shaped channels that run parallel to [001]. One K(+) cation [occupancy 0.73 (3)] is surrounded by nine O atoms, while the other K(+) cation [occupancy 0.23 (3)] is surrounded by eight O atoms.

KNi(0.93)Fe(II)(0.07)Fe(III)(PO4)2: a new type of structure for a compound of composition M(I)M(II)M(III)(PO4)2.

The solid solution KNi(0.93)Fe(II)(0.07)Fe(III)(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition M(I)M(II)M(III)(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069 (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1A and K1B, with occupancies of 0.930 (9) and 0.070 (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1A of [9 + 3] and for K1B of [10 + 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1A and K1B positions due to substitution of Ni by Fe in the (Ni/Fe) position.

NASICON-related Na3.4Mn0.4Fe1.6(PO4)3.

The solid solution, sodium [iron(III)/manganese(II)] tris-(orthophosphate), Na3.4Mn0.4Fe1.6(PO4)3, was obtained using a flux method. Its crystal structure is related to that of NASICON-type compounds. The [(Mn/Fe)2(PO4)3] framework is built up from an (Mn/Fe)O6octa-hedron (site symmetry 3.), with a mixed Mn/Fe occupancy, and a PO4 tetra-hedron (site symmetry .2). The Na⁺ cations are distributed over two partially occupied sites in the cavities of the framework. One Na⁺ cation (site symmetry -3.) is surrounded by six O atoms, whereas the other Na⁺ cation (site symmetry .2) is surrounded by eight O atoms.

KMg(0.09)Fe(1.91)(PO(4))(2).

KMg(0.09)Fe(1.91)(PO(4))(2), potassium [iron(II)/magnesium] iron(III) bis(orthophosphate), is a solid solution derived from compounds with general formula KM(II)Fe(PO(4))(2) (M(II) = Fe, Cu), in which the Mg atoms substitute Fe atoms only in the octa-hedrally surrounded sites. The framework of the structure is built up from [FeO(5)] trigonal bipyramids and [MO(6)] (M = (Fe, Mg) octa-hedra sharing corners and edges and connected by two types of bridging PO(4) tetra-hedra. The K(+) cations are nine-coordinated and are situated in channels running along [101].

K2M(III)2(M(VI)O4)(PO4)2 (M(III) = Fe, Sc; M(VI) = Mo, W), novel members of the lagbeinite-related family: synthesis, structure, and magnetic properties.

The possibility of PO(4)(3-) for MoO(4)(2-) partial substitution in the langbeinite framework has been studied by exploration of the K-Fe(Sc)-Mo(W)-P-O systems using the high-temperature solution method. It was shown that 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(2) with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.

Redetermination of AgPO(3).

Single crystals of silver(I) polyphosphate(V), AgPO(3), were prepared via a phospho-ric acid melt method using a solution of Ag(3)PO(4) in H(3)PO(4). In comparison with the previous study based on single-crystal Weissenberg photographs [Jost (1961 ▶). Acta Cryst. 14, 779-784], the results were mainly confirmed, but with much higher precision and with all displacement parameters refined anisotropically. The structure is built up from two types of distorted edge- and corner-sharing [AgO(5)] polyhedra, giving rise to multidirectional ribbons, and from two types of PO(4) tetra-hedra linked into meandering chains (PO(3))(n) spreading parallel to the b axis with a repeat unit of four tetra-hedra. The calculated bond-valence sum value of one of the two Ag(I) ions indicates a significant strain of the structure.

A novel In3O16 fragment in Cs3In3(PO4)4.

The double phosphate Cs(3)In(3)(PO(4))(4), prepared by a flux technique, features a fragment of composition In(3)O(16) formed by three corner-sharing InO(6) polyhedra. The central In atom resides on a twofold rotation axis, while the other two In atoms are on general positions. The O atoms in this fragment also belong to PO(4) tetrahedra, which link the structure into an overall three-dimensional anionic In-O-P network that is penetrated by tunnels running along c. Two independent Cs(+) cations reside inside the tunnels, one of which sits on a centre of inversion. In general, the organization of the framework is similar to that of K(3)In(3)(PO(4))(4), which also contains an In(3)O(16) fragment. However, in the latter case the unit consists of one InO(7) polyhedron and one InO(6) polyhedron sharing an edge, with a third InO(6) octahedron connected via a shared corner. Calculations of the Voronoi-Dirichlet polyhedra of the alkali metals give coordination schemes for Cs of [9+2] and [8+4] (1 symmetry), and for K of [8+1], [7+2] and [7+2]. This structural analysis shows that the coordination requirements of the alkali metals residing inside the tunnels cause the difference in the In(3)O(16) geometry.

The triple pyrophosphate Cs3CaFe(P2O7)2.

The complex phosphate tricaesium calcium iron bis(diphosphate), Cs(3)CaFe(P(2)O(7))(2), has been prepared by the flux method. Isolated [FeO(5)] and [CaO(6)] polyhedra are linked by two types of P(2)O(7) groups into a three-dimensional framework. The latter is penetrated by hexagonal channels along the a axis where three Cs atoms are located. Calculations of caesium Voronoi-Dirichlet polyhedra give coordination schemes for the three Cs atoms as [8 + 3], [9 + 1] and [9 + 4]. The structure includes features of both two- and three-dimensional frameworks of caesium double pyrophosphates.