Crystal structure of Cs[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)] · H<Subscript>2</Subscript>O

Single crystals of Cs[(UO₂)₂(C₂O₄)₂(OH)] · H₂O were synthesized and structurally studied using X-ray diffraction. The compound crystallizes in monoclinic space group P2₁/m, Z = 2, with the unit cell parameters a = 5.5032(4) Å, b = 13.5577(8) Å, c = 9.5859(8) Å, β = 97.012(3)°, V = 709.86(9) ų, R = 0.0444. The main building units of crystals are [(UO₂)₂(C₂O₄)₂(OH)]^? layers of the A₂K ₂ ⁰² M² (A = UO ₂ ²⁺ , K⁰² = C₂O ₄ ^2? , and M² = OH^?) crystal-chemical family. Uranium-containing layers are linked into a three-dimensional framework via electrostatic interactions with outer-sphere cations and hydrogen bonds with water molecules.     

Single-crystal <Superscript>1</Superscript>H NMR data and hydrogen atom disorder in lawsonite,CaAl<Subscript>2</Subscript>[Si<Subscript>2</Subscript>O<Subscript>7</Subscript>](OH)<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

The dynamic structure of hydrogen sublattice in lawsonite, CaAl₂[Si₂O₇](OH)₂·H₂O is studied by the solidstate proton magnetic resonance (¹H NMR) spectroscopy of single crystal at room temperature. It is shown that both encapsulated water molecules, and hydroxyl OH-groups undergoes the rocking librations of the amplitudes of ～20° for H₂O, and ～40° for hydroxyls.     

Crystal structure of Ba<Subscript>3</Subscript>[UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(NCS)]<Subscript>2</Subscript> · 9H<Subscript>2</Subscript>O

Single crystals of Ba₃[UO₂(C₂O₄)₂(NCS)]₂ · 9H₂O are synthesized and studied by X-ray diffraction. The crystals are orthorhombic, space group Fddd, Z = 16, and the unit cell parameters are a = 16.253(3) Å, b = 22.245(3) Å, c = 39.031(6) Å. The main crystal structural units are mononuclear complex groups [UO₂(C₂O₄)₂NCS]^3? of the crystal-chemical family (AB ₂ ⁰¹ M¹ (A = UO ₂ ²⁺ , B⁰¹ = C₂O ₄ ^2? , M¹ = NCS^?) of the uranyl complexes linked into a three-dimensional framework by electrostatic interactions and hydrogen bonds involving oxalate ions and water molecules.     

Crystal structure of [Pb<Subscript>3</Subscript>(OH)<Subscript>4</Subscript>Co(NO<Subscript>2</Subscript>)<Subscript>3</Subscript>](NO<Subscript>3</Subscript>)(NO<Subscript>2</Subscript>)·2H<Subscript>2</Subscript>O

The structure of [Pb₃(OH)₄Co(NO₂)₃](NO₃)(NO₂)·2H₂O is determined by single crystal X-ray diffraction. The crystallographic characteristics are as follows: a = 8.9414(4) Å, b = 14.5330(5) Å, c = 24.9383(9) Å, V = 3240.6(2) ų, space group Pbca, Z = 8. The Co(III) atoms have a slightly distorted octahedral coordination formed by three nitrogen atoms belonging to nitro groups (Co–N_av is 1.91 Å) and three oxygen atoms belonging to hydroxyl groups (Co–O_av is 1.93 Å). The hydroxyl groups act as μ₃-bridges between the metal atoms. The geometric characteristics are analyzed and the packing motif is determined.     

Balance,uniformity, and asymmetry of the structure of volborthite Cu<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>(V<Subscript>2</Subscript>O<Subscript>7</Subscript>)·2H<Subscript>2</Subscript>O

Four structural models of volborthite Cu₃(OH)₂(V₂O₇)·2H₂O (a = 10.646(2) Å, b = 5.867(1) Å, c = 14.432(2) Å, β = 95.19(1)°, V = 897.7(5) ų, Z = 4, R/R _w = 0.038/0.046) calculated in the space groups determined from the systematic absences are compared. Based on the structure balance and the similarity of constituting polyhedra, values of the R factor, and isotropic thermal parameters, the space group Ia is found to be preferable, which is the only possible asymmetric and uniform variant. Hydrogen atoms of OH-groups, oxygen atoms and, partially, hydrogen atoms of water are localized.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Synthesis and structure of new dinitrosyl iron complexes with bridging thiolate ligands [Fe<Subscript>2</Subscript>(μ-SR)<Subscript>2</Subscript>(NO)<Subscript>4</Subscript>]

Two new dinitrosyl iron complexes with bridging thiolate ligands [Fe₂(µ-SR)₂(NO)₄], where R = n-Hex or _cyclo-Hex, were synthesized and their molecular structures were analyzed. The structure of the [Fe₂(µ-S-n-Hex)₂(NO)₄] complex was determined by X-ray diffraction. For the [Fe₂(µ-S-cyclo-Hex)₂(NO)₄] complex, the geometry was assigned based on the results of structure-sensitive spectroscopic methods and DFT quantum chemical calculations.     

Crystal structure of nickel paratungstate B Ni<Subscript>5</Subscript>[W<Subscript>12</Subscript>O<Subscript>40</Subscript>(OH)<Subscript>2</Subscript>]·37H<Subscript>2</Subscript>O

From the solution of the system Na₂WO₄-HNO₃-Ni(NO₃)₂-H₂O acidified to Z = ν(H⁺)/ν(WO ₄ ^2? ) = 1.29, the green crystals of nickel paratungstate B Ni₅[W₁₂O₄₀(OH)₂]·37H₂O are isolated. By FTIR spectroscopy the isopoly anion is shown to belong to the structural type of paratungstate B. Using single crystal X-ray analysis, the structure of Ni₅[W₁₂O₄₀(OH)₂]·37H₂O is solved (M _r = 3840.36, monoclinic, P2₁/c space group, a = 21.9061(6) Å, b = 14.9297(4) Å, c = 22.1391(6) Å, β = 107.609(3)°, V = 6901.4(3)ų at T = 293 K, Z = 4, d_x = 3.696 g/cm³, F ₀₀₀ = 6944, μ = 21.368 mm^?1, ?33 ≤ h ≤ 33, ?22 ≤ k ≤ 22, ?33 ≤ l ≤33; the final uncertainty values for the observed reflections are R _F = 0.0532, wR ² = 0.0831 (R _F = 0.1088, wR ² = 0.0894 over all independent reflections), S = 0.978; CSD-421468).     

Thermogravimetric analysis of wheatleyite Na<Subscript>2</Subscript>Cu<Superscript>2+</Superscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC₂O₄ as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na₂Cu²⁺(C₂O₄)₂·2H₂O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.     

Research on photosensitivity of benzoquinones and benzoquinoneimines in the sunlight/Fe<Superscript>2+</Superscript>/S<Subscript>2</Subscript>O<Subscript>8</Subscript><Superscript>2−</Superscript> system

This paper investigated the photodegradation characteristics of benzoquinones and benzoquinoneimines. The photosensitivity of benzoquinones and benzoquinoneimines were analyzed by measuring the yield of SO ₄ ^?· in a light/Fe²⁺/S₂O₈ ^2? system and the degradation mechanism of benzoquinones, then discussed benzoquinoneimines in light/Fe²⁺/S₂O₈ ^2? and light/S₂O₈ ^2? system. The results revealed that a more aggressive oxidation of benzoquinones and benzoquinoneimines by the sunlight/Fe²⁺/S₂O₈ ^2? method showed a more rapid and more complete removal of chromaticity than that of the UV/Fe²⁺/S₂O₈ ^2? method. It was showed that they were photosensitizers, and they could generate ¹O₂ and O ₂ ^?· which could promote the formation of SO ₄ ^?· and ^·OH in the sunlight system. Nevertheless, for benzoquinones, the sunlight/S₂O₈ ^2? method was superior to the UV/S₂O₈ ^2? method. For benzoquinoneimines, the sunlight/S₂O₈ ^2? method was inferior to the UV/S₂O₈ ^2? method. In addition, the yield of SO ₄ ^?· in the sunlight/Fe²⁺/S₂O₈ ^2? system was more than that of the UV/Fe²⁺/S₂O₈ ^2? system. Therefore, the photosensitivity of benzoquinones is superior to benzoquinoneimines in water treatment.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Crystal structure of Bi<Subscript>36</Subscript>MgP<Subscript>2</Subscript>O<Subscript>60 − δ</Subscript>

A compound with the general formula Bi₃₆MgP₂O_{60 ? δ} was obtained by a solid-state reaction method. Its composition was confirmed using EDAX. The compound belongs to the cubic crystal system (space group I23, no. 197) and has a sillenite-type structure. The lattice parameter a _o is 10.15704(12) Å. The Rietveld refinement of the crystallographic data revealed mixed tetrahedral sites (2a) occupied by Mg, P, and Bi in a ratio of 32: 63: 5. The resulting lattice strains are compensated by vacancies in the cationic (2a) and anionic sites (24f) and by distortion of the Bi-O framework detected by IR and Raman spectroscopy.     

Synthesis,structure, and some reactions of the cluster complex [(μ-H)<Subscript>2</Subscript>Fe<Subscript>5</Subscript>(μ<Subscript>3</Subscript>-Se)<Subscript>2</Subscript>(CO)<Subscript>14</Subscript>]

In the reaction of Na₂Se with [Fe(CO)₅] in isopropanol with subsequent acidification with HCl, which is used to synthesize [(μ-H)₂Fe₃(μ₃-Se)(CO)₉] (II), the cluster [(μ-H)₂Fe₅(μ₃-Se)₂(CO)₁₄] (I) was detected. In assumption that compound I could serve as a suitable synthon for preparing the bulky heterometallic clusters, its reactions with the Rh-containing complexes were studied. The reaction of I with [Rh(CO)₂Cp*] (Cp* is pentamethylcyclopentadienyl) was found to give a mixture of the products. The main reaction products were isolated and their structures were determined: [Fe₂Rh(μ₃-Se)₂(CO)₆Cp*], [Fe₂Rh(μ₃-Se)(μ₃-CO)(CO)₆Cp*], [FeRh₂(μ₃-Se)(μ-CO)(CO)₃Cp ₂ ^* ], [Fe₂Rh₂(μ₄-Se)(μ-CO)₄(CO)₂Cp ₂ ^* ]. Potassium hydride treatment of II with subsequent addition of [Cp*Rh(CH₃CN)₃](CF₃SO₃)₂ leads to the well-known cluster complex [Fe₃Rh(μ₄-Se)(CO)₉Cp*]. A set of the reaction products indicates that the {Fe₅Se₂} core cannot be used as one-piece “building block” in the synthesis of heterometallic clusters.     

Synthesis of Ca<Subscript>3</Subscript>Al<Subscript>6</Subscript>Si<Subscript>2</Subscript>O<Subscript>16</Subscript>: Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> phosphors by sol–gel method and optical properties

Ca₃Al₆Si₂O₁₆: Ce³⁺, Tb³⁺ phosphors have been prepared by sol–gel method. The structure and photoluminescence properties were studied with careful. The results indicated that the single-phased Ca₃Al₆Si₂O₁₆ phosphors crystallize at 1,000 °C for 2 h in conventional furnace. With appropriate concentrations of Ce³⁺ and Tb³⁺ ions into Ca₃Al₆Si₂O₁₆ matrix, these materials exhibit blue phosphors and white light under ultraviolet radiation. White-light emission can be achieved because of a 400 nm emission ascribed to transitions of Ce³⁺ ions and three sharp peaks at 487, 543, 585 nm, respectively, resulting from transitions of Tb³⁺ ions.     

Crystal structure of Na<Subscript>4</Subscript>[Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>6</Subscript>] · 10H<Subscript>2</Subscript>O

Single crystals of the Na₄[Na₂Cr₂(C₂O₄)₆] · 10H₂O complex were synthesized for the first time. The structure of the complex was determined by X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system with the unit cell parameters a = 17.290(4) Å, b = 12.521(3) Å, c = 15.149(3) Å, β = 100.45(3)°, Z = 4, space group Cc. Anionic layers [NaCr(C₂O₄)₃] _2n ^4n? can be distinguished in the crystal structure of the complex. The Na⁺ cations and water molecules, involved in the formation of a hydrogen bond network, are located between the anionic layers.     

Experimental Determination of the Isotherm at 15°C of the System Mg<Superscript>2+</Superscript>/Cl<Superscript>−</Superscript>, SO<Subscript>4</Subscript><Superscript>2</Superscript>–H<Subscript>2</Subscript>O

Summary.  The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.  Corresponding author. E-mail: ariguib@planet.tn Received October 16, 2002; accepted (revised) December 3, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70^th birthday     

A theoretical study on the dynamics of the gas phase reaction of NH<Subscript>2</Subscript>(<Superscript>2</Superscript>B<Subscript>1</Subscript>) with HO<Subscript>2</Subscript>(<Superscript>2</Superscript>A″)

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH₂(²B₁)] with hydroperoxyl radical [HO₂(²A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH₂O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H₂O as the major products.     

Single-phased white-light emitting CaAl<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>: Eu<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript> phosphors prepared by a sol–gel method

CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors have been prepared by a sol–gel method. X-ray diffractometer, spectrofluorometer and UV–Vis spectrometer were used to characterize structural and optical properties of the samples. The results indicate that anorthite (CaAl₂Si₂O₈) directly crystallizes at 1000 °C in the sol–gel process. CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors show two emission bands excited by ultraviolet light. Blue (around 415 nm) and yellow (around 575 nm) emissions originate from Eu²⁺ and Mn²⁺, respectively. With appropriate tuning of Mn²⁺ content, CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors exhibit different hues and relative color temperatures.     

Crystal structure of Pb<Subscript>2</Subscript>[Fe(CN)<Subscript>6</Subscript>]NO<Superscript>3</Superscript>·5.5H<Subscript>2</Subscript>O

Synthesis of a mixed complex compound Pb₂[Fe(CN)₆]NO₃·5.5H₂O is described. The results of its X-ray structural investigation are presented. Crystal data: C₆H₁₁FeN₇O_8.50Pb₂: a = 7.2582(6) Å, b = 21.838(3) Å, c = 11.612(1) Å; β = 107.91(1)°, V = 1751.4(3) ų, Z = 4, d_calc = 2.986 g/cm³, space group P2₁/m, R = 0.038. The compound has a framework polymer structure.     

Concentration Space of Homogeneous Garnet in the System Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–(Y,Bi)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The concentration space of homogeneous garnet in the system Ga₂O₃–(Y, Bi)₃(Fe, Ga)₅O₁₂–Fe₂O₃ was determined by X-ray powder diffraction analysis. The obtained results expand the knowledge of the possible variations of cation ratios Y : Bi : Fe : Ga in garnet, which can be used for searching for and creating new stable magneto-optical materials.