Search results for "Powder diffraction"
showing 10 items of 243 documents
The crystal structure of 3,5-diisopropyl-4-nitropyrazole from X-ray powder diffraction data
2001
The crystal structure of 3,5-diisopropyl-4-nitropyrazole, 3c, has been determined by a Patterson Search method from laboratory X-ray powder diffraction data. The crystal data are: monoclinic symmetry with the unit-cell parameters aa 19:530O5U; ba 6:485O1U and ca 17:937O3U A; ba 100:32O1U8; space group I2/a ,C 9H15N3O2, Za 8, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found were refined by a least-squares technique. A whole pattern- fitting program was used to extract the integrated intensities. The structure was solved taking a related compound as a search model and the final Rietveld refinement converged to Rwpa 0.1971 and Rpa 0.1437. The structure pr…
Crystal structure of a new polytype in the V–P–O system: is ω-VOPO4 a dynamically stabilised metastable network?
2001
Abstract ω-VOPO 4 has been prepared by thermal decomposition of different oxovanadium hydrogen phosphates, namely VO(HPO 4 ) n H 2 O ( n =2( α ), 2(β) and 4) and β-NH 4 (VO 2 )(HPO 4 ). The ω-VOPO 4 phase only remains well crystallised at relatively high temperatures. Its crystal structure has been determined ab initio from X-ray powder diffraction data collected at 475°C. The cell is tetragonal (space group P4 2 /mmc) with a =4.8552(3) A and c =8.4301(6) A. Starting positional parameters were obtained by direct methods, and the structure was refined using Rietveld profile refinement principles. Disorder of two oxygen sublattices is observed. To rationalise some features of the crystal stru…
Protective effect of mesoporous silica particles on encapsulated folates.
2016
Mesoporous silica particles (MSPs) are considered suitable supports to design gated materials for the encapsulation of bioactive molecules. Folates are essential micronutrients which are sensitive to external agents that provoke nutritional deficiencies. Folates encapsulation in MSPs to prevent degradation and to allow their controlled delivery is a promising strategy. Nevertheless, no information exists about the protective effect of MSPs encapsulation to prevent their degradation. In this work, 5-formyltetrahydrofolate (FO) and folic acid (FA) were entrapped in MSPs functionalized with polyamines, which acted as pH-dependent molecular gates. The stability of free and entrapped vitamins af…
Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reaction: a multi-technique mechanistic study.
2015
Despite an absence of conventional porosity, the 1D coordination polymer [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)3 ] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)3 (ROH)2 ] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)×10(-5) (MeOH), 9.5(3)×10(-6) (EtOH), 6.14(5)×10(-5) (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH→1→2, in which 2 is the 2D coordination polymer [Ag4 (O2 …
The structural versatility of proton sponge bismuth halides
2022
Hybrid halometalates containing lead, tin, bismuth and antimony and organic cations have recently shown a bevy of interesting photophysical properties. Aiming at finding chemically stable and thermally inert species, three halobismutate species of this class, crystallized with proton sponge-derived cations (PRSH), have been isolated as microcrystalline powders by mixing 1,8-bis(dimethylamino)-naphthalene (proton sponge, or PRS) and bismuth oxide in concentrated HX acids (X = Cl, Br and I). The two isomorphous (PRSH)3Bi2X9 (X = Br, I) species, containing isolated [Bi2X9]3- anions, are triclinic at room temperature and convert upon heating into a monoclinic structure through a displacive …
From nitrides to carbides: topotactic synthesis of the η-carbides Fe3Mo3C and Co3Mo3C
2004
The molybdenum bimetallic interstitial carbides Fe(3)Mo(3)C and Co(3)Mo(3)C have been synthesized by temperature-programmed reaction (TPR) between the molybdenum bimetallic interstitial nitrides Fe(3)Mo(3)N and Co(3)Mo(3)N and a flowing mixture of CH(4) and H(2) diluted in Ar. These compounds have been characterized by X-ray diffraction, laser Raman spectroscopy, elemental analysis, energy dispersive analysis of X rays, thermal analysis (in air) and scanning electron microscopy (field emission). Their structures have been refined from X-ray powder diffraction data. These carbides crystallize in the cubic system, space group Fd3m[a= 11.11376(6) and 11.0697(3)[Angstrom] for Fe and Co compound…
Structural and magnetic studies of mononuclear lanthanide complexes derived from Ν-rich chiral Schiff bases.
2021
Zn(II) complexes containing N, N,N and N,N,N pyridine (dPy) ligands tend to display improved fluorescence efficiencies in comparison with their starting ligands benefiting from the chelation enhanced effect (CHEF) and preventing photoinduced electron transfer (PET) mechanisms by the coordination of their lone pair electrons. Nevertheless, the size of Zn(II) makes steric crowding an important factor to be considered, since it can promote the elongation of the coordination bonds that weakens their strength and favors the reduction of fluorescence efficiencies through PET processes. For that reason, in this contribution we have performed a systematic study of Zn(II) compounds based on α-acetam…
One‐Pot Synthesis of a New High‐Aluminium‐Content Super‐Microporous Aluminosilicate
2006
A new super-microporous aluminosilicate having a high aluminium content (Si/Al ca. 1) has been prepared through a surfactant-assisted procedure with the use of a commercially available binary precursor (di-sec-butoxyaluminooxytriethoxysilane) as a single source of both Al and Si. The formation of super-micropores is a result of a significant network shrinkage associated with the thermal elimination of the surfactant. This solid has been studied by X-ray powder diffraction, electron microscopy, nuclear magnetic resonance spectroscopy and porosimetry. A preliminary analysis of the acidity and the catalytic activity of the super-microporous solid for the selective catalytic reduction of NOx is…
Crystal Structures and Polymorphism of Nickel and Copper Coordination Polymers with Pyridine Ligands
2014
The crystal structures of a series of pyridine coordination polymers [MIICl2(C5H5N)x]n (M = Ni, Cu), prepared via thermal decomposition are reported. [NiCl2(C5H5N)4] (1) decomposes stepwise via [NiCl2(C5H5N)2]n (2), [NiCl2(C5H5N)]n (3), and [NiCl2(C5H5N)2/3]n (4), to NiCl2 with increasing temperature. The thermal decomposition of [CuCl2(C5H5N)2]n (5), progresses via two polymorphs of [CuCl2(C5H5N)]n (6a and 6b), and [CuCl2(C5H5N)2/3]n (7), to CuCl2. The compounds 3, 4, and 7 were prepared as pure phases. All crystal structures were determined by X-ray powder diffraction. Notably, the crystal structures of the polymorphs 6a and 6b were determined from powder diffraction data of a mixture of …
Interaction of Alkaline Metal Cations with Oxidic Surfaces: Effect on the Morphology of SnO2 Nanoparticles
2010
Reaction pathways to SnO(2) nanomaterials through the hydrolysis of hydrated tin tetrachloride precursors were investigated. The products were prepared solvothermally starting from hydrated tin tetrachloride and various (e.g., alkali) hydroxides. The influence of the precursor base on the final morphology of the nanomaterials was studied. X-ray powder diffraction (XRD) data indicated the formation of rutile-type SnO(2). Transmission electron microscopy (TEM) studies revealed different morphologies that were formed with different precursor base cations. Data from molecular dynamics (MD) simulations provide theoretical evidence that the adsorption of the cations of the precursor base to the f…