Refinement of the crystal structure of lithium-bearing uvite

The crystal structure of a natural calcium tourmaline, i.e., uvite with a high lithium content (0.51 au per formula (aupf) at the Y site, is refined to R = 0.019, R _w = 0.020, and S = 1.11. It is shown that, in nature, there exist uvites in which the charge balance in the case where the Z site is occupied by trivalent cations is provided by the replacement of part of the divalent magnesium cations at the Y site by univalent cations, divalent calcium cations at the X site by sodium cations, and univalent anions at the W site by oxygen anions. The W site is found to be split into two sites, namely, the W1 and W11 sites (the W1–W11 distance is 0.14 Å), which are partially occupied by the fluorine and oxygen anions, respectively. An analysis of the results obtained in this study and the data available in the literature on the crystal structure of uvites allows the conclusion that uvite can be considered a superspecies and that the nomenclature of this mineral group needs refinement with the use of structural data.     

Refinement of the crystal structure of sanidine-like feldspar

The crystal structure of sanidine-like feldspar of the composition KAlSi₃O₈ from the Khibiny alkaline massif (the Kola Peninsula) has been refined (X-ray diffraction analysis; automated Syntex $P\bar 1$ diffractometer; 2θ: θ scanning technique; 2320 reflections; R _(hkl) = 0.0409; anisotropic refinement; AREN program package). The data obtained for KAlSi₃O₈ are: a = 8.615(9), b = 13.030(7), c = 7.200(5) Å, α = 89.99(5)°, β = 116.01(6)°, γ = 89.98(7)°, Z = 4, sp. gr. $C\bar 1$ . Microtwinning revealed in the crystal structure of the mineral explains the simultaneous existence of two structural-optical types in one sample—“high” and “low” sanidines.     

Refinement of the crystal structure of acetylacetonatodicarbonylrhodium(I)

The structure of acetylacetonatodicarbonylrhodium(I), Rh(acac)(CO)₂, has been refined from three-dimensional X-ray diffractometer data. The complex crystallises in the triclinic space groupP¯1 with two molecules in a unit cell of dimensionsa = 6.5189(5),b = 7.7614(8),c = 9.2049(12)Å, = 106.04(1), = 91.15(1), = 100.21(1) °. Full-matrix least-squares refinement, using 1456 independent reflections, has reachedR = 0.038.The rhodium atom has a square-planar coordination with two Rh-O(acac) distances of 2.040 and 2.044Å, and two Rh-C(carbonyl) distances both equal to 1.831Å, the O-Rh-O angle is 90.8 ° and the C-Rh-C angle is 88.9 °. All twelve non-hydrogen atoms are closely planar, with an average deviation of 0.003Å, and a maximum deviation of 0.006Å, from the least-squares plane through the molecule. A second non-crystallographic plane of symmetry bisects the molecule, which therefore has essentiallymm2 (C _2v ) point symmetry. The molecules stack in such a way that the rhodium atoms of neighbouring molecules occupy the two remaining pseudo-octahedral positions, with Rh...Rh distances of 3.253 and 3.271Å.     

Refinement of the crystal structure of Na2Ti3O7

The crystals of Na₂Ti₃O₇ were obtained by crystallization from flux. The structure of the compound was refined from X-ray diffraction data collected on a four-circle diffractometer (2θ/θ scanning technique, λMoK _α radiation, graphite monochromator, θ_max = 40°). The crystals are monoclinic a = 9.133(2) Å, b = 3.806(1) Å, c = 8.566(2) Å, β = 101.57(3)°, sp. gr. P2₁/m, Z = 2, ρ_calcd = 3.435 g/cm³, R = 0.035, 1241 reflections with I ≥ 2σ(I). The geometric characteristics of the Ti-polyhedra are analyzed as to their positions in the trioctahedral ribbon. The polymorphism of the {Ti₃O₇}^2? anionic radical in the structures of Na₂Ti₃O₇ and PbTi₃O₇ is described. The topology and dimensionality of the { Ti₃O₇}^2? anionic radical are demonstrated to depend on the type of the large cations located at the lattice points of the hexagonal close packing characteristic of both structures.     

Refinement of the crystal and molecular structure of tetraacetylethane by neutron diffraction

The structure of tetraacetylethane has been determined by neutron diffraction. The compound exists in the dienolic form, the enolic hydrogen being intramolecularly bonded to a neighbouring oxygen in a clearly asymmetric mode. The acetylacetonate residues are essentially planar.     

Refinement of the crystal structure of calcioancylite-(Ce) by the Rietveld method

The crystal structure of calcioancylite-(Ce) of the (Ca_0.30Sr_0.22)_Σ0.52(Ce_0.78La_0.47Nd_0.16Pr_0.05Sm_0.02)_Σ1.48(CO₃)₂((OH)_1.20F_0.28)_Σ1.48 · 1.97H₂O composition from alkali hydrothermalites of Mont Saint-Hilaire, Canada, has been refined by the Rietveld method. The refinement details are as follows: ADP-2 diffractometer, λCuK _α radiation, Ni filter, 10.50° < 2θ < 140.00°, and the number of reflections (α₁ + α₂) 652. All calculations have been performed within the sp. gr. Pmcn (a = 5.0095(1) Å, b = 8.5006(1) Å, c = 7.2670(1) Å, V = 309.46(1) ų, R _wp = 3.45) in the anisotropic approximation of thermal vibrations for cations.     

Refinement of the crystal structure of malonic acid,C3H4O4

A reinvestigation of the X-ray crystal structure of malonic acid (C₃H₄O₄) has been made in the light of some observations arising from solid-state¹³C NMR studies on this compound. The unit cell parameters are:a=5.156(1),b=5.341(1),c=8.407(1) Å, =71.48^o (2), =76.12^o (2), =85.09^o (2), space group ,Z=2. The structure was solved by direct methods and refined by full-matrix least-squares refinement to a finalR value of 0.038 for 711 unique reflections withl>3. The packing of the molecules involves dimeric hydrogen bonded association of each carboxyl group with a centrosymmetrically related neighbor. The angles O–C–O (123.3^o and 124.8^o, respectively) for the two carboxyl groups agree qualitatively with the values predicted from a linear relationship relating the observed ₂₂ component of the Carbon-13 NMR chemical shielding tensor for the carboxyl carbon atom to the bond angle O–C–O at the carbon atom.Contribution No. 825.     

New data on vlasovite: Refinement of the crystal structure and the radiation damage of the crystal during the x-ray diffraction experiment

The crystal structure of vlasovite obtained from the Kipawa alkaline complex in Quebec is refined to R _F = 0.053 for 1515 unique reflections with |F| > 4σ(F). The parameters of the monoclinic unit are as follows: a = 11.063(8) Å, b = 10.15(1) Å, c = 8.60(1) Å, β = 100.3(1)°, space group C2/c, and Z = 4. The X-ray diffraction, electron microprobe, and IR spectroscopic data indicate that, under X-ray radiation, the specimen suffers radiation damage, which is accompanied by a partial removal of Na atoms, incorporation of H₂O molecules into the structure, and, possibly, a change in the configuration of the (Si,O) framework.     

Refinement of the crystal structures of three fluorine-bearing elbaites

The crystal structures of three Li-Al natural tourmalines (elbaites) containing 0.88–1.39 wt % F are refined to R= 0.0294, 0.0308, and 0.0417. It is revealed that the W threefold anion site is split into two sites, namely, the W1 threefold site and W2 ninefold site (W1–W2 ～ 0.4 Å, Y-W₁ ≥ 1.94 Å, Y-W2 ≥ 1.75 Å). The following hypothesis is proposed and justified: the W1 and W2 sites are partially occupied by OH groups and fluorine anions, respectively. The ratio of the [YO₄(OH)₂] octahedra to the [YO₄(OH)F] octahedra depends on the fluorine content and varies from structure to structure. The fact that the W site is more than 50% occupied by fluorine in the structures of two tourmalines under investigation allows the conclusion that fluor-elbaite with the ideal formula Na(Li_1.5A1_1.5)A1₆(Si₆O₁₈)(BO₃)₃(OH)₃F is a new mineral species and that elbaite can be considered a superspecies.     

Refinement of the molecular structure of Aureomycin

The data for Aureomycin have been refined by full-matrix least-squares, including anisotropic thermal parameters for the heavy atoms and isotropic parameters for the hydrogen atoms. The positional parameters are generally similar to those published previously. The amide group remains anomalous. All hydrogen atoms except the crucial one in the amide group were located in a difference map. The final value ofR for the set of visual data is 10.6%.     

Refinement of the crystal structure of calcium-lithium-aluminum tourmaline from the pegmatite vein in the Sangilen Upland (Tuva Republic)

The crystal structure of a natural calcium-lithium-aluminum tourmaline, which has the unique composition (Ca_0.62Na_0.32□_0.06)(Al_1.08Li_0.99Fe _0.66 ²⁺ Mg_0.24Ti_0.03)Al₆[Si₆O₁₈](BO₃)₃(OH_2.28O_0.72) · (F_0.84O_0.16), is refined (R = 0.019, R _w = 0.022, S = 1.47). It is found that the O(1)(W) site is split into two sites, O(1) and O(11), which are incompletely occupied by fluorine and oxygen anions, respectively, and that the O(3)(V) site contains bivalent oxygen anions. The solid solution studied is close in composition to the liddicoatite mineral species and differs from the latter one by the Li: Al ratio in the Y octahedra and the presence of bivalent oxygen anions in the O(3) site. The tourmaline studied differs from the hypothetical oxyliddicoatite by the population of the O(1)(W) site by fluorine and accommodation of additional oxygen anions in the O(3)(V) site.     

Refinement of the crystal and molecular structure of 3,5-diamino-1,2,4-dithiazolium bromide. Comparative investigation on the thiouret hydrohalides

The crystal and molecular structure of 3,5-diamino-1,2,4-dithiazolium bromide has been refined from three-dimensional counter data (856 reflections) by least-squares methods, anisotropically for the nonhydrogen and isotropically for the hydrogen atoms, to a finalR=0.036:a=9.948(1),b=12.731(1),c=5.098(1) Å, B=98.70(1)° at 18°C,Z=4,P2₁/n. The S-S (2.075 Å) distance is intermediate between those of the thiouret hydrochloride and hydroiodide. The C-N(terminal) and C-N(bridging) distances are close to their average value (1.322 Å) within their standard deviations. Thev(NH₂) and (NH₂) frequencies of the thiouret hydrohalides are close to those of dithiobiuret while thev(NH) and (NH) bands are, as expected, absent. Thev(CN) andv(CS) bands are shifted to higher and lower frequencies, respectively, while a newv(SS) broad band is observed in the 430–410 cm^–1 region.     

Refinement of the crystal structures of synthetic nickel- and cobalt-bearing tourmalines

The crystal structures of synthetic tourmalines with a unique composition containing 3d elements (Ni, Fe, and Co) have been refined: (Ca_0.12?_0.88)(Al_1.69Ni _0.81 ²⁺ Fe _0.50 ²⁺ )(Al_5.40Fe _0.60 ³⁺ )(Si_5.82Al_0.18O₁₈)(BO₃)₃(OH)_3.25O_0.75 I, a = 15.897(5), c = 7.145(2) Å, V = 1564(1) Å; Na_0.91(Ni _1.20 ²⁺ Cr _0.96 ³⁺ Al_0.63Fe _0.18 ²⁺ Mg_0.03)(Al_4.26Ni _1.20 ²⁺ Cr _0.48 ³⁺ Ti_0.06)(Si_5.82Al_0.18)O₁₈(BO₃)₃(OH)_3.73O_0.27 II, a = 15.945(5), c = 7.208(2) Å, V = 1587(1) ų and Na_0.35(Al_1.80Co _1.20 ²⁺ )(Al_5.28Co _0.66 ²⁺ Ti_0.06)(Si_5.64B_0.36)O₁₈(BO₃)₃(OH)_3.81O_0.19 III, a = 15.753(8), c = 7.053(3) Å, V = 1516(2) ų. The reliability factors are R ₁ = 0.038?0.057 and wR ₂ = 0.041–0.060. It is found that 3d elements occupy both Y- and Z positions in all structures. The excess positive charge is compensated for due to the incorporation of divalent oxygen anions into the O3(V)+O1(W) positions.     

Refinement of the atomic structure of CdTe single crystals

A comparative refinement of the anharmonic and disordered models of the atomic structure was performed based on precision X-ray diffraction data sets collected from a CdTe single crystal at 295, 376, 491, and 583 K. Although both models provide the asymmetric contributions of Cd and Te to the structure factors, the anharmonic model seems to be more advantageous.     

Refinement of the crystal structure of lead titanate with different degrees of imperfection of cationic and anionic sublattices by the Rietveld method

The parameters of the crystal structure of lead titanate with different degrees of imperfection of the anionic and cationic sublattices are refined by the Rietveld method. The experiments are carried out on a DRON-4 diffractometer (CuK_α radiation; 20° < 2θ < 70°; scan step, 0.01°; exposure time per point, 10 s). All the calculations are performed with the GSAS software package in the space group P4mm. The structure parameters are refined in the isotropic approximation to R_d = 5.0–6.0%.     

Refinement of composition and structure of holtite I

A new version of the structural formulas of holtite I, (Al_0.61Ta_0.25□)(Al_0.96□)₂(Al_0.96□)₂ × (Al_0.90□)₂(Si_2.49Sb_0.35As_0.13)O_13.46(O_0.48OH_0.52)(BO₃), is reported. The main changes in this formula are related to the incorporation of arsenic atoms in (Sb,As)O₃ pyramides into the structure.