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PubMed2000

Trimerization of NaC2N3 to Na3C6N9 in the solid: ab initio crystal structure determination of two polymorphs of NaC2N3 and of Na3C6N9 from X-ray powder diffractometry.

Sodium dicyanamide NaC2N3 was found to undergo two phase transitions. According to thermal analysis and temperature-dependent X-ray powder diffractometry, the transition of alpha-NaC2N3 (1a) to beta-NaC2N3 (1b) occurs at 33 degrees C and is displacive. 1a crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 647.7(1), b = 1494.8(3), c = 357.25(7) pm, beta = 93.496(1) degrees, and Z = 4. The structure was solved from powder diffraction data (Cu Kalpha1, T = 22 degrees C) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.072, Rp = 0.053, and RF = 0.074. 1b crystallizes in the orthorhombic system, space group Pbnm (no. 62), with a = 650.15(5), b = 1495.1(2), c = 360.50(3) pm, and Z = 4. The structure was refined by the Rietveld method using the atomic coordinates of 1a as starting values (Mo Kalpha1, T = 150 degrees C). The final agreement factors were wRp = 0.044, Rp = 0.034, RF = 0.140. The crystal structures of both polymorphs contain sheets of Na+ and N(CN)2- ions which are in la nearly and in 1b exactly coplanar. Above 340 degrees C, 1b trimerizes in the solid to Na3C6N9 (2). 2 crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 1104.82(1), b = 2338.06(3), c = 351.616(3) pm, beta = 97.9132(9)degrees, and Z = 4. The structure was solved from synchrotron powder diffraction data (lambda = 59.733 pm) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.080, Rp = 0.059, and RF = 0.080. The compound contains Na+ and the planar tricyanomelaminate C6N9(3-). The phase transition from 1b to 2 is reconstructive. It occurs in the solid-state without involvement of other phases or intermediates. The crystal structures of 1b and 2 indicate that there is no preorientation of the N(CN)2- in the solid before their trimerization to C6N9(3-).

Journal Article↗
PubMed2002

Physical stability of solid dispersions of the antiviral agent UC-781 with PEG 6000, Gelucire 44/14 and PVP K30.

This paper describes the physical stability of solid dispersions of UC-781 with PEG 6000, Gelucire 44/14 and PVP K30 prepared by the solvent and melting methods. The concentration of the drug in the solid dispersions ranged from 5 to 80% w/w. The solid dispersions were stored at 4-8 and 25 degrees C (25% RH), then their physicochemical properties were analysed by differential scanning calorimetry (DSC), X-ray powder diffraction and dissolution studies as a function of storage time. The DSC curves of solid dispersions of UC-781 with PVP K30 did not show any melting peaks corresponding to UC-781 after storage, indicating no recrystallization of the drug. The DSC data obtained from PEG 6000 and Gelucire 44/14 showed some variations in melting peak temperatures and enthalpy of fusion of the carriers. It was shown that the enthalpy of fusion of PEG 6000 in the dispersions increased after storage; it was more pronounced for samples stored at 25 degrees C compared to those at 4-8 degrees C indicating the reorganization of the crystalline domains of the polymer. Similarly, the enthalpy of fusion of Gelucire 44/14 in the solid dispersions increased as a function of time. Dissolution of UC-781 from all solid dispersions decreased as a function of storage time. While these observations concurred with the DSC data for all solid dispersions, they were not reflected by X-ray powder diffraction data. It was concluded that it is the change of the physical state of the carriers and not that of the drug, which is responsible for the decreased dissolution properties of the solid dispersions investigated.

Anilides↗
PubMed2003

Dehydration studies using a novel multichamber microscale fluid bed dryer with in-line near-infrared measurement.

The purpose of this research was to study the effect of two process parameters (temperature and moisture content) on dehydration behavior of different materials using a novel multichamber microscale fluid bed dryer with a process air control unit and in-line near-infrared (NIR) spectroscopy. The materials studied were disodium hydrogen phosphates with three different levels of hydrate water and wet theophylline granules. Measured process parameters of fluid bed drying were logged, including in-line NIR signals. Off-line analyses consisted of X-ray powder diffraction patterns, Fourier transform NIR spectra and moisture contents of studied materials. During fluid bed drying, the stepwise dehydration of materials was observed by the water content difference of inlet and outlet air, the pressure difference over the bed, and the in-line NIR spectroscopy. The off-line analysis confirmed the state of solid materials. The temperature and the moisture content of the process air were demonstrated to be significant factors for the solid-state stability of theophylline. The presented setup is a material and cost-saving approach for studying the influence of different process parameters on dehydration behavior during pharmaceutical processing.

Desiccation↗
PubMed2006

Structure determination of A2M3+TaO6 and A2M3+NbO6 ordered perovskites: octahedral tilting and pseudosymmetry.

The room-temperature crystal structures of six A(2)M(3+)M(5+)O(6) ordered perovskites have been determined from neutron and X-ray powder diffraction data. Ba(2)YNbO(6) adopts the aristotype high-symmetry cubic structure (space group Fm\overline 3m, Z = 4). The symmetries of the remaining five compounds were lowered by octahedral tilting distortions. Out-of-phase rotations of the octahedra about the c axis were observed in Sr(2)CrTaO(6) and Sr(2)GaTaO(6), which lowers the symmetry to tetragonal (space group = I4/m, Z = 2, Glazer tilt system = a(0)a(0)c(-)). Octahedral tilting analogous to that seen in GdFeO(3) occurs in Sr(2)ScNbO(6), Ca(2)AlNbO(6) and Ca(2)CrTaO(6), which lowers the symmetry to monoclinic (space group P2(1)/n, Z = 2, Glazer tilt system = a(-)a(-)c(+)). The Sr(2)MTaO(6) (M = Cr, Ga, Sc) compounds have unit-cell dimensions that are highly pseudo-cubic. Ca(2)AlNbO(6) and Ca(2)CrTaO(6) have unit-cell dimensions that are strongly pseudo-orthorhombic. This high degree of pseudosymmetry complicates the space-group assignment and structure determination. The space-group symmetries, unit-cell dimensions and cation ordering characteristics of an additional 13 compositions, as determined from X-ray powder diffraction data, are also reported. An analysis of the crystal structures of 32 A(2)MTaO(6) and A(2)MNbO(6) perovskites shows that in general the octahedral tilt system strongly correlates with the tolerance factor.

Journal Article↗
PubMed2002

Synthesis and characterization of Pt(CN-p-(C(2)H(5))C(6)H(4))(2)(CN)(2), a crystalline vapoluminescent compound that detects vapor-phase aromatic hydrocarbons.

The vapochromic and vapoluminescent compound Pt(CN-p-(C(2)H(5))C(6)H(4))(2)(CN)(2) (abbreviated PtC(2)) is conveniently synthesized by the thermal rearrangement of [Pt(CN-p-(C(2)H(5))C(6)H(4))(4)][Pt(CN)(4)]. Recrystallization of PtC(2) gives a crystalline orange morph (O-PtC(2)) and an amorphous purple morph (P-PtC(2)) that both contain the cis isomer and differ only in their solid-state packing arrangements. Both compounds were fully characterized by elemental analysis, X-ray powder diffraction, NMR, IR, and TGA. O-PtC(2) is vapochromic and vapoluminescent: it reversibly sorbs aromatic hydrocarbons and ethanol from air or nitrogen with resulting color changes and shifts in the emission spectrum. The lambda(max) values (nm) for emission from O-PtC(2) x (guest) are as follows: no guest, 611; toluene, 565; benzene, 586; chlorobenzene, 592; p-xylene, 585; mesitylene, 565; ethanol, 587. In the case of toluene and mesitylene, intermediate emitting phases are observed. Recrystallization of O-PtC(2) from dichloromethane/toluene gave single crystals of PtC(2) x 0.5(toluene). The single-crystal X-ray structure of PtC(2) x 0.5(toluene) contains infinite stacks of cis geometry and planar molecules with chains of platinum atoms parallel to the c axis of the monoclinic unit cell. The average Pt-Pt separation in PtC(2) x 0.5(toluene) is c/4 = 3.288(2) A. There are solvent channels parallel with the c axis that contain the toluene molecule guests. Thin films of O-PtC(2) rapidly sorb toluene from the gas phase to form PtC(2) x 0.25(toluene) and PtC(2) x 0.5(toluene). Long-term exposure gives PtC(2) x 1.0(toluene). Removal of the toluene source causes rapid desorption to PtC(2) x 0.5(toluene) and then to PtC(2) x 0.25(toluene). The remaining 0.25(toluene) lattice guests require heating for rapid removal. X-ray powder diffraction identified the PtC(2),PtC(2) x .25(toluene), and PtC(2) x 0.5(toluene) phases and showed that the sorption of toluene is accompanied by small changes in the unit cell dimensions that include lengthening the Pt-Pt distances in the structure. The sorption process improves the packing in the structure by utilizing some of the free volume for the toluene lattice guests.

Journal Article↗
PubMed2002

Pressure-induced volume expansion of zeolites in the natrolite family.

Powder diffraction patterns of the zeolites natrolite (Na(16)Al(16)Si(24)O(80).16H(2)O), mesolite (Na(5.33)Ca(5.33)Al(16)Si(24)O(80).21.33H(2)O), scolecite (Ca(8)Al(16)Si(24)O(80).24H(2)O), and a gallosilicate analogue of natrolite (K(16)Ga(16)Si(24)O(80).12H(2)O), all crystallizing with a natrolite framework topology, were measured as a function of pressure up to 5.0 GPa with use of a diamond-anvil cell and a 200 microm focused monochromatic synchrotron X-ray beam. Under the hydrostatic conditions mediated by an alcohol and water mixture, all these materials showed an abrupt volume expansion (ca. 2.5% in natrolite) between 0.8 and 1.5 GPa without altering the framework topology. Rietveld refinements using the data collected on natrolite show that the anomalous swelling is due to the selective sorption of water from the pressure-transmission fluid expanding the channels along the a- and b-unit cell axes. This gives rise to a "superhydrated" phase of natrolite with an approximate formula of Na(16)Al(16)Si(24)O(80).32H(2)O, which contains hydrogen-bonded helical water nanotubes along the channels. In mesolite, which at ambient pressure is composed of ordered layers of sodium- and calcium-containing channels in a 1:2 ratio along the b-axis, this anomalous swelling is accompanied by a loss of the superlattice reflections (b(mesolite) = 3b(natrolite)). This suggests a pressure-induced order-disorder transition involving the motions of sodium and calcium cations either through cross-channel diffusion or within the respective channels. The powder diffraction data of scolecite, a monoclinic analogue of natrolite where all sodium cations are substituted by calcium and water molecules, reveal a reversible pressure-induced partial amorphization under hydrostatic conditions. Unlike the 2-dimensional swelling observed in natrolite and mesolite, the volume expansion of the potassium gallosilicate natrolite is 3-dimensional and includes the lengthening of the channel axis. In addition, the expanded phase, stable at high pressure, is retained at ambient conditions after pressure is released. The unprecedented and intriguing high-pressure crystal chemistry of zeolites with the natrolite framework topology is discussed here relating the different types of volume expansion to superhydration.

Journal Article↗
PubMed2005

Synthesis, structure, and luminescent property of a heterometallic metal-organic framework constructed from rod-shaped secondary building blocks.

A new heterometallic MOF compound, [ZnNa(m-BDC)2].NH2(CH3)2 (MOF-CJ2), has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, X-ray powder diffraction, ICP, TGA, IR, and photoluminescence spectroscopy analyses. It crystallizes in monoclinic space group C2/c (No. 15) with a=13.277(6) A, b=14.323(7) A, c=11.328(6) A, and beta=111.73(2) degrees. Its framework is constructed from M-O-C (M=Na and Zn) rods composed of alternating six-coordinated Na(I) centers and four-coordinated Zn(II) centers. These rods are linked by m-BDC links to form primitive cubic (pcu) type rod packing. This framework exemplifies the first open-framework heterometallic MOF structure based on the assembly of infinite rod building units.

Journal Article↗
PubMed2006

Synthesis and characterization of a 3D coordination polymer based on trinuclear triangular CuII as secondary building units.

The hydrothermal reaction of Cu(II) salts with 1,2,4-triazole (Htrz) in aqueous ammonia yielded a novel metal-organic framework {[Cu3(mu3-O)(mu3-trz)3(OH)(H2O)6]}n (1), which was characterized by single-crystal X-ray diffraction, X-ray powder diffraction, thermogravimetric analysis, IR, and variable-temperature magnetic susceptibility. It crystallizes in cubic, space group Fd3c with a = 24.644(3) A, V = 14967(3) A(3), and Z = 96. Its framework is the first 3D structure using coordinative interactions constructed via trinuclear triangular Cu(II) secondary building units, in which both Cu(II) ions and trz ligands act as three-connected nodes to form a 6.8(2) net. An overall antiferromagnetic behavior was found in the compound.

Journal Article↗
PubMed2005

Templated metal-organic frameworks: synthesis, structures, thermal properties and solid-state transformation of two novel calcium-adipate frameworks.

Two novel calcium-adipate framework materials have been synthesized hydrothermally. GWMOF-7 ([Ca(C6H8O4)(H2O)2]*(C10H8N2)) and GWMOF-8 ([Ca(C6H8O4)(H2O)2]*(C12H12N2)) both formed three-dimensional structures and were characterized with single-crystal X-ray diffraction, powder X-ray diffraction, IR spectroscopy and elemental analysis. Thermal properties were also studied with thermogravimetric analysis, and show that these structures undergo a solid-state transformation into a denser three-dimensional framework.

Journal Article↗
PubMed2002

Dichlorobis(2-methylquinoline N-oxide-kappaO)zinc(II) from powder data.

The crystal structure of the title compound, [ZnCl(2)(C(10)H(9)NO)(2)], has been determined from laboratory powder diffraction data. Although the powder pattern was initially indexed with tetragonal unit-cell dimensions, the correct solution was found in an orthorhombic space group using a combination of grid-search and simulated-annealing techniques. The subsequent bond-restrained Rietveld refinement gave bond lengths and angles within expected ranges. The molecule has crystallographically imposed twofold symmetry.

Crystallography, X-Ray↗
PubMed2005

Powder neutron diffraction of Tl2BeF4 at six temperatures from room temperature to 1.5 K.

The structure of thallium fluoroberyllate, Tl2BeF4, has been analysed by the Rietveld method on neutron diffraction patterns collected at 1.5, 50, 100, 150, 200 and 300 K, with the aim of detecting low-temperature instabilities. Atomic parameters based on the isomorphic beta-K2SO4 crystal in the paraelectric phase were used as the starting model at room temperature; no evidence for any phase transition has been detected at lower temperature. The structure was determined in the orthorhombic space group Pnma. All the atoms (except one F atom) occupy sites with m symmetry. We have compared the structure with those of other compounds of the beta-K2SO4 family, at room temperature, in order to gain insight into their observed instabilities. The irregular coordination of the cations may indicate stereochemical activity of the TlI lone pair but does not indicate a possible structural instability.

Journal Article↗
PubMed2000

The crystallography beamline I711 at MAX II.

A new X-ray crystallographic beamline is operational at the MAX II synchrotron in Lund. The beamline has been in regular use since August 1998 and is used both for macro- and small molecule diffraction as well as powder diffraction experiments. The radiation source is a 1.8 T multipole wiggler. The beam is focused vertically by a bendable mirror and horizontally by an asymmetrically cut Si(111) monochromator. The wavelength range is 0.8-1.55 A with a measured flux at 1 A of more than 10(11) photons s(-1) in 0.3 mm x 0.3 mm at the sample position. The station is currently equipped with a Mar345 imaging plate, a Bruker Smart 1000 area CCD detector and a Huber imaging-plate Guinier camera. An ADSC 210 area CCD detector is planned to be installed during 2000.

Journal Article↗
PubMed2006

Synthesis and characterization of uncapped gamma-Fe2O3 nanoparticles prepared by flame pyrolysis of ferrocene in ethanol.

Nanoparticles of iron(III) oxide were synthesized by spontaneous combustion of ferrocene in ethanol solution using a simple spirit lamp. X-ray powder diffraction and electron diffraction analysis of the powder suggested the formation of gamma-Fe2O3 (Maghemite phase) having lattice constant 8.3539 +/- 0.0209 A. Transmission Electron Micrograph suggested the formation of spherical particles with an average diameter of 24.7 +/- 1.6 nm. A sextet with an isomeric shift of 0.328 mm s(-1) seen in the Mossbauer spectrum recorded at room temperature, further supports the formation of gamma-Fe2O3. The particles were dispersed freely in the polar solvents like ethanol, dimethyl sulfoxide, and water. Infra Red spectrum gave bands at 400, 432, 565, and 638 cm(-1), which confirms the presence of gamma-Fe2O3 phase.

Crystallization↗
PubMed2005

High-pressure neutron diffraction study of superhydrated natrolite.

Neutron powder diffraction data were collected on a sample of natrolite and a 1:1 (v/v) mixture of perdeuterated methanol and water at a pressure of 1.87(11) GPa. The natrolite sample was superhydrated, with a water content double that observed at ambient pressure. All of the water deuterium atoms were located and the nature and extent of the hydrogen bonding elucidated for the first time. This has allowed the calculation of bond valence sums for the water oxygen atoms, and from this, it can be deduced that the key energetic factor leading to loss of the additional water molecule upon pressure release is the poor coordination to sodium cations within the pores.

Journal Article↗
PubMed2004

[X-ray diffraction quantitative analysis with polynomial-fit method for polycrystalline materials].

The polynomial-fit method for XRD quantitative analysis of polycrystalline materials is presented in this paper, which combines a mathematic function model with computer technology. Based on the construction of diffraction peak mathematic function model, the XRD atlases from experiments were analyzed by means of polynomial whole pattern fitting to the spectral lines using computer software, then the integral intensities of every peak and weight percentages of each phase could be obtained accurately. This paper mainly includes three parts: 1. According to the fact that the diffraction atlases of mixture are weighted superposition of the powder diffraction atlases of each component and the weight factor of each component is relevant to its volume fraction or weight percentage, the theory of polynomial whole pattern fitting is constructed and the weight factor and weight percentage can be worked out. 2. Describe the method and procedure of data acquisition and analysis. 3. Discuss the result of quantitative analysis. The polynomial-fit method not only simplifies the process of data handling, but also increases the accuracy of analytical result.

Algorithms↗