Study of the ionic conductivity of some fluorides of monovalent and tetravalent elements

Recently some interest has attached to ionic conductivity in the fluorides of metals with large cation radius because of the high fluorine mobility in these materials.A.c. conductivity measurements using the complex impedance method were carried out on sintered samples and showed that some binary fluorides of monovalent elements (M^I = K, Rb, Tl) and tetravalent elements (M^IV = Zr,Hf, Th, U) exhibit an appreciable ionic conductivity at moderate temperature : σ at 200°C (Ω^?1 cm^?1) Tl₃ZrF₇ 3.5 × 10^?3 Tl₂ZrF₆ 1.1 × 10^?2 Tl ZrF₅ 5 × 10^?4A single crystal study of Tl₃ZrF₇ shows that this compound crystallizes in the cubic system with space group Fm3m and cell parameter a = 9.34 Å. Therefore its crystal structure may be related to that of (NH₄)₃ZrF₇ [1 to 3] which is characterized by the presence of (ZrF₇)^3? ions with a pentagonal bipyramid as probable configuration. There are two crystallographically independent fluorine ions in position (96 j) of the space group Fm3m with a percentage of occupancy of 20.8 and 8.3 respectively. Thus Tl₃ZrF₇ is an example of fluoride where a three dimensional ionic conductivity occurs due to an incomplete occupation of a special symmetry position and where temperature increase might create rotation of (ZrF₇)^3? polyhedra giving rise to an important anionic disorder.In order to determine the origin of the ionic conductivity in TlZrF₅ we have undertaken the determination of the crystal structure of this fluoride from X-ray intensity measurements made with the aid of an automatic four circle diffractometer.TlZrF₅ cristallizes in the monoclinic system with unit-cell dimensions a = 8.112(1)Å, b = 7.927(3)Å, c = 7.929(1)Å, β = 123.99(1)° and space group P2 /c (No 14), Z = 4.In this structure, the Zr⁴⁺ ion is surrounded by eight F^? ions, the coordination polyhedron being a bicapped trigonal prism. This crystal structure consists of sheets (ZrF₅)^? that may be described as edge-shared and corner-shared bicapped trigonal prisms (ZrF₈). The sheets run parallel to the yOz plane and are bonded together by the Tl⁺ ions which are surrounded by twelve F^?ions. This arrangement produces relatively open tunnels in the b direction delimited by the cations. Of the five independent fluorine atoms, two of them, namely F(1) and F(4) are different from the other from the point of view of bonding and are located in these tunnels. Thus they are probably primarily responsible for the high conductivity of this material [4].With regard to Tl₂ZrF₆, it is the best as far as ionic conductivity is concerned. However its crystal structure is still unknown and its determination is actually under investigation in our laboratory.All this materials are good electronic insulators and their transport properties due to the high fluorine ion mobilities allow us to think that some of them hold considerable promise for use as solid electrolytes.     

Détermination de la structure cristalline du ferrite de baryum Ba2Fe6O11

The crystal structure of dibarium triferrite Ba₂Fe₆O₁₁ has been solved by direct methods, using intensity data collected by means of an automated diffractometer (MoKα radiation) and corrected for absorption. It crystallizes in the orthorhombic space group Pnnm: a = 23.024(10)Å, b = 5.181(3) Å, c = 8.900(4) Å, Z = 4. Program MULTAN was successfully used for locating Ba²⁺ and most of the Fe³⁺ ions. The structure was further refined by conventional Fourier and least-squares methods (full-matrix program) to a final R value of 0.045 for 1448 observed reflections. Fe³⁺ ions occur in both octahedral (FeO mean distance: 2.02 Å) and tetrahedral (FeO mean distance: 1.865 Å) coordination. Two types of Ba²⁺ ions are found, with six and seven neighboring oxygen atoms. The structure consists of sheets of edge-shared FeO₆ octahedra which are connected by means of corner-shared tetrahedra.     

Synthesis and crystal structure of α-Ba2ZrF8 and Pb2ZrF8 determined ab initio from synchrotron and neutron powder diffraction data

α-Ba₂ZrF₈ is prepared as systematically twinned crystals by hydrothermal synthesis (200°C) or as fine powders either on a sand bath (60°C) (aqueous HF medium) or by solid state reaction at 450°C. Synchrotron radiation was used because of ambiguities in indexations from conventional X-ray (pseudo-hexagonal symmetry). The structure was determined ab initio from synchrotron powder data. Neutron data were used for improving accuracy because some degree of non-stoichiometry was suspected. The cell is orthorhombic, space group Prima, Z = 4, with a = 9.7401(1) Å, b = 5.6147(1) Å and c = 11.8871(1) Å (synchrotron data, 25°C). The final neutron Rietveld refinement led to R_P = 8.4 % and R_B = 3.5 % for the stoichiometric Ba₂ZrF₈ formulation (sand bath sample). The structure is built up from [ZrF₈] bicapped trigonal prisms isolated in a kinked fluorite matrix. The isostructural Pb₂ZrF₈ compound prepared in solution is also examined. An unexpected relationship with NaBaZrF₇ is discussed.     

The crystal structure of the 2:5 phase in the K2OZrO2 system: K4Zr5O12, a compound with octahedral and trigonal prismatic zirconium(IV) coordination

K₄Zr₅O₁₂ crystallizes in the trigonal system with unit-cell dimensions a = 5.821(2) Å, c = 10.437(3) Å, and space group $\text{P}\text{3}\text{m1}$. The structure was solved by Patterson and Fourier techniques. the 386 unique reflections measured by counter techniques were reduced to 334 with I ? 3σ (I); these were used in full-matrix least-squares refinement of the model to a conventional R of 0.0196 (ωR = 0.0228). K₄Zr₅O₁₂ has a structure that may be described as consisting of perovskite-like layers (potassium ions are cube octahedrally coordinated) with sheets of hexagonal rings of edge-shared trigonal prismatically coordinated zirconium(IV) ions inserted between every third and fourth layer of the perovskite-like structure. The trigonal prisms are face shared to octahedra above and below alternately to form cavities that are occupied by pairs of potassium ions in ninefold coordination.     

Synthesis and x-ray crystal structure of OsBr2(CNBut)4·2CH2Cl2

Reaction of (NH₄)₂OsBr₆ with excess Na/Hg in THF in the presence of excess ^tBuNC yields trans-OsBr₂(CNBu^t)₄ in high yield. The bis-dichloromethane solvate crystallises from CH₂Cl₂ solutions and its X-ray crystal structure has been determined. Crystal data: C₂₂H₄₀Br₂Cl₄N₄Os, M = 852.40, monoclinic, space group P2₁/c, a = 9.702(3) Å, b = 10.143(5) Å, c = 18.497(5) Å, β = 104.28(3)°, U = 1764(1) ų, Z = 2 for D_c = 1.60 gcm^?3. λ(MoK_α) = 0.71069 Å (graphite monochromator), μ(MoK_α) = 65.44 cm^?1, final R = 0.044, R_w = 0.056 from 1105 observed reflections (1777 measured).     

Crystal structure of (glycine) sodium nitrate Gly·NaNO3

The crystal structure of Gly·NaNO₃ was determined by single crystal diffraction methods (monoclinic crystal system, B11n, a = 14.339(3) Å, b = 9.136(3) Å, c = 5.263(3) Å, γ = 119.14(5)°). The structure is built from alternating layers of glycine organic molecules and inorganic layers consisting of Na⁺ ions and planar NO ₃ ^? ions stretching along the b axis. The surroundings of the Na atom include the oxygen atoms of the NO ₃ ^? groups and the oxygen atoms of glycine molecules. The structure has a system of hydrogen bonds.     

Crystal structure of polymer hexaaqua-hexakis(2-thiobarbiturato)dieuropium(III)

Complex [Eu₂(HTBA)₆(H₂O)₆] _n (I), where H₂TBA is 2-thiobarbituric acid C₄H₄N₂O₂S, is synthesized. Its structure is determined by X-ray diffraction analysis (CIF file CCDC 987519). The crystals of complex I are monoclinic: a = 14.1033(4) Å, b = 10.0988(4) Å, c = 15.4061(5) Å, β = 110.003(1)°, V = 2061.9(1) ų, space group P2/n, Z = 2. All three independent ligands HTBA^? are coordinated to Eu³⁺ through oxygen atoms. Six HTBA^? ions (two terminal and four bridging) and two water molecules are coordinated to one of the independent Eu³⁺ ions. The second Eu³⁺ ion is bound to four bridging HTBA^? ions and four water molecules. The coordination polyhedra are square antiprisms. The bridging HTBA^? ions join the antiprisms into layers. The structure is stabilized by numerous hydrogen bonds and the π-π interaction between HTBA^?.     

The crystal structure of a new nonstoichiometric phase Cs1−xLu3F10−x (x ⋍ 0.25)

A high-temperature phase with the formula $\text{Cs}{}_{\mathrm{1?x}}\text{Lu}{}_3\text{F}{}_{\mathrm{10?x}}\text{(x ? 0.25)}$ has been characterized during the investigation of the CsFLuF₃ system. This phase crystallizes in the monoclinic system with unit-cell dimensions a = 13.764(5) Å, b = 7.947(1) Å, c = 4.299(2)Å, β = 90.04(5)° and space group Cm (No. 8), Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares techniques to a conventional R of 0.053 (R_w = 0.079) for 2038 independent reflections recorded on an automatic four-circle diffractometer. The structure may be regarded as built up of (Lu₃F₁₀)^? layers that may be described as corner- and edge-shared LuF₇ pentagonal bipyramids. These layers run parallel to the (001) plane. The structure extends along the third direction by cornersharing involving axial vertices of the pentagonal bipyramids. This three-dimensional framework delimits tunnels running parallel to the c direction where the Cs⁺ ions lie. The partial occupancies of both the Cs site and one out of the seven independent fluorine sites results in the nonstoichiometry.     

Syntheses and structures of nine-coordinate K3[DyIII(nta)2(H2O)]·5H2O and eight-coordinate (NH4)3[DyIII(nta)2] complexes

K₃[Dy^III(nta)₂(H₂O)]·5H₂O and (NH₄)₃[Dy^III(nta)₂] have been synthesized in aqueous solution and characterized by IR, elemental analysis and single-crystal X-ray diffraction techniques. In K₃[Dy^III(nta)₂(H₂O)]·5H₂O the Dy^III ion is nine coordinated yielding a tricapped trigonal prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 15.373(5) Å, b = 12.896(4) Å, c = 26.202(9) Å; β = 96.122(5)°, V = 5165(3) ų, Z = 8, D _c = 1.965 g·cm^?3, μ = 3.458 mm^?1, F(000) = 3016, R ₁ = 0.0452 and wR ₂ = 0.1025 for 4550 observed reflections with I ≥ 2σ(I). In (NH₄)₃[Dy^III(nta)₂] the Dy^III ion is eight coordinated yielding a usual dicapped trigonal anti-prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 13.736(3) Å, b = 7.9389(16) Å, c = 18.781(4) Å; β = 104.099(3)°, V = 1986.3(7) ų, Z = 2, D _c = 1.983 g·cm^?3, μ = 3.834 mm^?1, F(000) = 1172, R ₁ = 0.0208 and wR ₂ = 0.0500 for 2022 observed reflections with I ≥ 2σ(I). The results indicate that the difference in counter ion also influences coordination numbers and structures of rare earth metal complexes with aminopolycarboxylic acid ligands.     

Crystal structure of cerium(III) diammonium polyphosphate (NH4)2Ce(PO3)5

Cerium(III) diammonium polyphosphate, (NH₄)₂Ce(PO₃)₅, is triclinic P1 with the following unit cell dimensions: a = 7.241(5) Å, b = 13.314(8) Å, c = 7.241(5)Å, α = 90.35(5)°, β′ = 107.50(5)°, γ = 90.28(5)°, and Z = 2, V = 665.7 ų, D_x = 2.85 g/cm³. The crystal structure of this new type of polyphosphate has been solved and refined from 4130 independent reflections to a final R value 0.029. The most interesting feature of this salt is the existence of two infinite crystallographically nonequivalent (PO₃)^?_∞ chains, one running parallel to the a axis, the other along the c axis, both with a period of five tetrahedra. This compound seems to be the first example of a long chain polyphosphate with crystallographic independent chains.     

Die Kristallstruktur des Hydrazinium-monofluorids

The hydrazinium monofluoride N₂H₅F crystallizes with orthorhombic symmetry, space group P2₁2₁2₁,a=4.592 Å,b=8.217 Å,c=12.341 Å, and 8 formula units. The structure was determined by the permutation method in projection, and by the three-dimensionalPatterson function, refined by Full-Matrix-Least-Squares (R=0.056). The structure consists of N₂H₅ ⁺- and F^?-ions, bonded with hydrogen bonds N?H ... N and N?H ... F. Each N₂H₅ ⁺ ion is surrounded by four F^?-ions and two nitrogen atoms of two different N₂H₅ ⁺ ions. Each F^? ion is connected with four different N₂H₅ ⁺ ions.     

Synthesis and crystal structure of the silver nitrate complex with 4,4′-trimethylenedipiperidine [Ag(C<Subscript>13</Subscript>H<Subscript>26</Subscript>N<Subscript>2</Subscript>)]NO<Subscript>3</Subscript>

A new coordination compound [AgNO₃(C₁₃H₂₆N₂)] was synthesized and structurally characterized. The crystals are triclinic: space group P \(\bar 1\), a = 6.157(1) Å, b = 10.074(1) Å, c = 14.153(1) Å, α = 102.36(1)°, β = 92.16(1)°, γ = 107.33(1)°, V = 813.7(2) ų, ρ_calcd = 1.552 g/cm³, Z = 2. The structure contains centrosymmetric rings formed by two Ag⁺ ions and two bridging trimethylenedipiperidine ligands. The coordination of Ag⁺ ions is close to linear (Ag(1)-N(1), 2.192(5) Å; Ag(1)-N(2), 2.212(5) Å; angle N(1)Ag(1)N(2), 162.7(2)°). Anions NO ₃ ^? form weak bonds with silver ions (Ag(1)…O(1), 2.783(5) Å; Ag(1)-O(3), 2.893(5) Å) and combine rings into supramolecular bands running in the diagonal direction of the unit cell.     

New hydrogen-bonded dimeric and polymeric gold(I) complexes of the heterodifunctional ligand Ph2PNHP(O)Ph2

The preparation of several new gold(I) complexes by chloride metathesis of [AuCl(HL)] [HL=Ph₂PNHP(O)Ph₂] with either HL or K[Ph₂P(E)NP(E)Ph₂] (E=S or Se) is described. All compounds were characterised by a combination of ³¹P{¹H}, ¹H and IR spectroscopy, microanalysis and X-ray crystallography. X-ray structural studies reveal that [Au(HL)₂]Cl [monoclinic, space group P2₁/c, a=9.0726(3) Å, b=21.0847(6) Å, c=12.0131(3) Å, β=105.1090(10)°, V=2219 ų, Z=2, final R=3.97] forms a one dimensional polymeric structure in which alternating [Au(HL)₂]⁺ and Cl⁻ ions are linked through intermolecular N–H⋯Cl hydrogen-bonding. In contrast the three-co-ordinate compound [Au{Ph₂P(Se)NP(Se)Ph₂-Se,Se′}(HL)] [monoclinic, space group P2₁/a, a=21.6752(5) Å, b=9.1200(10) Å, c=24.0742(7) Å, β=106.080(2)°, V=4573 ų, Z=4, final R=8.94] forms hydrogen-bonded dimer pairs analogous to that previously observed in non-complexed HL. The X-ray crystal structure of the gold(I) precursor [AuCl(HL)] has also been determined: monoclinic, space group P2₁/c, a=10.217(8) Å, b=23.256(5) Å, c=20.086(5) Å, β=101.15(4)°, V=4683 ų, Z=8, final R=5.2. The X-ray crystal structure reveals intermolecular N–H⋯OP hydrogen-bonding between adjacent [AuCl(HL)] molecules forming infinite chains.     

Structural chemistry of Ba2CdS3, Ba2CdSe3, BaCdS2, BaCu2S2 and BaCu2Se2

The structures of all compounds were determined from three dimensional single crystal X-ray diffraction data and refined by least squares. Ba₂CdS₃ and Ba₂CdSe₃ are isostructural, Pnma, a = 8.9145(6)Å, b = 4.3356(2)Å, c = 17.2439(9)Å for the former compound and a = 9.2247Å, b = 4,4823(6)Å, c = 17.8706(11)Å for the latter, z = 4, R = 0.0751 and R = 0.0462, respectively. The compounds are isostructural with the previously reported Mn analogues and with K₂AgI₃. Cd ions are in tetrahedral environment and the tetrahedra form infinite linear chains by corner sharing. Ba ions are in 7-fold coordination in which 6 anions form a trigonal prism and 1 anion caps one of the rectangular faces. BaCdS₂, Pnma, a = 7.2781(3)Å, b = 4.1670(1)Å, c = 13.9189(6)Å, z = 4, R = 0.0685. Cd ions can be considered to have a triangular planar coordination with CdS distances of 2.47 and 2.53 Å (twice). Two additional S ions are at 2.89 and 3.22 Å to complete a triangular bipyramidal configuration. Ba is in 7-fold coordination with the anions forming a trigonal prism which is capped on one rectangular face. The compound is isostructural with BaCdO₂ and is related to the structure of BaMnS₂. BaCdSe₂ could not be prepared. BaCu₂S₂ and BaCu₂Se₂ are isostructural, Pnma, a = 9.3081(4)Å, b = 4.0612(3)Å, c = 10.4084(5)Å for the sulfide and a = 9.5944(6)Å, b = 4.2142(4)Å, c = 10.7748(8)Å for the selenide, z = 4, R = 0.0634 and 0.0373, respectively. Ba ions are in the usual 7-fold, capped hexagonal prism, coordination. However, 9 Cu ions also can be considered to form a trigonal prism with all rectangular faces capped, around Ba since the BaCu distances range from 3.24 to 3.54 Å for the sulfide and from 3.37 to 3.67 Å for the selenide. One of the Cu ions is in a very distorted tetrahedral environment and the second one is located in a more regular tetrahedral configuration of the anions. Two independent infinite chains of tetrahedra are present. They are formed by sharing of two adjacent edges of each tetrahedron and then these chains in turn are linked by corner sharing into a three-dimensional network of tetrahedra.     

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) : XVI. The crystal and molecular structure of the compound [HAlNCH(CH3)C6H5]6·13 C6H14

The crystal structure of [HAlNCH(CH₃)C₆H₅] ₆·$\text{1}\text{3}$ C₆H₁₄ has been determined by single crystal three-dimensional X-ray analysis. Block-matrix least-squares refinement led to conventional R factor of 0.08. The molecule is built up of a prismatic hexagonal framework, (AlN)₆. Average AlN distances are 1.893(6) and 1.981(7) Å in the six-membered rings and in transverse bonds, respectively. Crystal data: hexagonal, space group P6₃, a 22.296(5), c 18.144(4) Å, V 7811.2 ų, Z = 6, D_c 1.16 g cm^?3.     

The crystal structure of tert-butyl coumarin-3-carboxylate

The crystal structure of tert-butyl coumarin-3-carboxylate has been determined. This compound crystallizes in the triclinic space group P-1 with cell parameters a = 5.8038(9) Å, b = 9.3022(16) Å, c = 12.421(2) Å, β = 97.107(5)°, V = 610.71(17) Å3, D _calc = 1.339 mg m^?3, and Z = 2. The final R value is 0.0593 for 2396 reflections. The adjacent molecules form a cyclic dimer by intermolecular hydrogen bonds of type C=O...H with their carbonyl group and the hydrogen on C(3).     

THE CRYSTAL,MOLECULAR STRUCTURE AND LIGAND BONDING IN TETRAKIS (N,N′-DIMETHYLTHIOUREA) NICKEL (II) BROMIDE DIHYDRATE

Abstract

The crystal structure of tetrakis(N,N′-dimethylthiourea)nickel(II) bromide dihydrate has been determined by three-dimensional x-ray diffraction from 1916 counter-data reflections collected at room temperature.

The structure consists of Ni[SC(NH)₂(CH₃)₂]²⁺ ₄ molecular ions, Br^? ions and waters of hydration. The nickel is located on a center of symmetry and is coordinated to four sulfur atoms in a square planar configuration. The waters of hydration and the bromide ions are involved in hydrogen bonding to the N,N′-dimethylthiourea (dmtu) groups. The orientation of the dmtu groups is such that two bond through the sulfur sp² orbital and the others bond through the π-orbitals of the dmtu group. The Ni-S distances are 2.204 ± 0.002 Å and 2.230 ± 0.002 Å, and the Ni-S-C angles are 106.2 ± 0.2Å and 110.3 ± 0.3°. The dmtu groups are planar except for methyl hydrogens.

The crystals are monoclinic, P2₁/a with a = 13.424 ± 0.002 Å, b = 12.321 ± 0.005 Å, c = 8.460 ± 0.008 Å β = 107.07 ± 0.05°, ρ₀ = 1.67 g cm^?3, ρ_c = 1.66 g cm^?3 and Z = 2. The structure was refined by full-matrix least-squares to a conventional R of 0.0466.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

Structural studies in the Li2MoO4MoO3 system: Part 1 the low temperature form of lithium tetramolybdate,LLi2Mo4O13

LLi₂Mo₄o₁₃ crystallizes in the triclinic system with unit-cell dimensions a = 8.578 Å, b = 11.450 Å, c = 8.225 Å, α = 109.24°, β = 96.04°, γ = 95.95° and space group $\text{P}\text{1}\text{, Z = 3}$. The calculated and measured densities are 4.02 g/cm³ and 4.1 g/cm³ respectively. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 2468 unique reflections collected by counter methods, 1813 with I ? 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.031 (ωR = 0.038). LLi₂Mo₄O₁₃ is a derivative of the V₆O₁₃ structure with oxygen ions arranged in a face-centred cubic type array with octahedrally coordinated molybdenum and lithium ions ordered into layers.     

Manifestations of noncovalent interactions in the solid state. Dimeric and polymeric self-assembly in imidazolium salts via face-to-face cation—cation π-stacking

Abstract

X-ray crystallographic investigation of the tertiary structure of simple 1-methylimidazolium (1-Meim) salts reveals that cation—cation face-to-face π—stacking with interplanar separations in the range typically seen for molecule—molecule and molecule—cation interactions are possible. Two salts are reported. 1-Meim-CF₃SO₃, 1, exists as a centrosymmetric dimer with an interplanar separation of only 3.16 Å. The two imidazolium rings are slipped to the extent that the interaction can be regarded as a manifestation of C—H…C—H dipole interactions. 1-Meim-NO₃ exists as a one-dimensional (1-D) polymer with interplanar separations of 3.65 Å. The cations are not as severely slipped as for 1 and the interactions can be regarded as the result of cation—cation and anion—anion complementary electrostatics. Semi-empirical calculations are used to rationalize the π-π stacking in both 1 and 2. Crystal data: 1-Meim-CF₃SO₃, 1, triclinic, P1, a=6.416(3) Å, b=7.617(4) Å, c=9.569(4) Å, α=85.36(4)°, β=86.08(3)°, γ=85.18(4)°, V=463.6(4) Å,³ Z=2, D_c =1.66 g cm^?3, μ=3.7 cm^?1, T=17°C, R=0.054 and R _w=0.076 for 1241 reflections; 1-Meim-NO₃, 2, monoclinic, P2₁/c, a=9.009(7) Å, b=9.988(6) Å, c=7.308(5) Å, β=94.93(6)°, V=655.2(8) Å,³ Z=4, D_c =1.47 g cm^?3, μ=1.2 cm^?1, T=17°C, R=0.060 and R _w=0.068 for 483 reflections.