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     

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.     

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.     

Structural investigation of salts containing ions [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [IrF<Subscript>6</Subscript>]<Superscript>2–</Superscript>

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.     

Interaction of [В<Subscript>10</Subscript>H<Subscript>10</Subscript>]<Superscript>2–</Superscript> and [В<Subscript>12</Subscript>H<Subscript>12</Subscript>]<Superscript>2–</Superscript> with nitro compounds

The interaction of the [B₁₀H₁₀]^2– and [B₁₂H₁₂]^2– anions with aliphatic and aromatic nitro compounds (RNO₂, where R = Et, n-Pr, i-Pr, tert-Bu, Ph) has been studied under irradiation with visible and UV light. It has been shown that, depending on the reaction conditions, both mono- and disubstituted nitro-closo-decaborates can be selectively obtained in yields up to 50%.     

Mechanistic and kinetic study the reaction of O(<Superscript>3</Superscript>P) + CH<Subscript>3</Subscript>CFCH<Subscript>2</Subscript>

The triplet potential energy surface of the O(³P) + CH₃CFCH₂ reaction has been investigated at the BMC-CCSD//MP2/6-311++G(d,p) level. Multichannel RRKM theory and transition state theory are employed to calculate the rate constants over a wide range of temperatures and pressures. The total rate constants show positive temperature dependence and pressure independence. At pressure of 10 Torr with He as bath gas, the addition/elimination on triplet potential energy surface is a dominant pathway. Major predicted end products are CH₃CFCHO (I) and H at the temperatures between 200 and 3,000 K; the direct hydrogen abstraction leading to OH + CH₂CFCH₂(I) plays an important role at higher temperatures. The calculated overall rate constants are in good agreement with the available experimental data.     

Isothermal solubility diagram of the 2Na<Superscript>+</Superscript>,Mg<Superscript>2+</Superscript>‖2Cl<Superscript>−</Superscript>, 2ClO<Stack><Subscript>3</Subscript><Superscript>‒</Superscript></Stack>-H<Subscript>2</Subscript>O quaternary system at 20 and 100°C

The solubility in the 2Na⁺,Mg²⁺‖2Cl⁻, 2ClO₃⁻-H₂O system was studied at 20 and 100°C and the solubility diagrams were plotted. New compounds were not found to form in the title quaternary reciprocal system. The sodium chloride field was observed to expand with rising temperature.     

Mercury complex [(HOCH<Subscript>2</Subscript>)<Subscript>3</Subscript>CNH<Subscript>3</Subscript>]<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> [HgI<Subscript>4</Subscript>]<Superscript>2−</Superscript>: Synthesis and structure

The complex [(HOCH₂)₃CNH₃] ₂ ⁺ [HgI₄]^2? (I) was synthesized by reacting (trioxymethyl)methylammonium iodide with mercury dioide (2: 1 mol/mol) in acetone. X-ray crystallography shows that the complex consists of two types of crystallographically independent [(HOCH₂)₃CNH₃]⁺ cations and tetrahedral anions [HgI₄]^2? (IHgI, 106.49(2)°–113.99(4)°; Hg-I, 2.7849(8)-2.8105(8) Å. [(HOCH₂)₃CNH₃]⁺ cations are linked via hydrogen bonds O…H-N and O-H…N (O…N, 2.84–2.92 Å) to form polymer chains, which are cross-linked with one another via anions (I…H, 2.81, 2.82 Å).     

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.     

Study on nonlinear kinetic and thermodynamics of oscillating reaction of amino Acid-BrO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>-Mn<Superscript>2+</Superscript>-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-acetone system

With the help of the kinetic parameters (the rate constant (k _in k _p) and the apparent activation energy (E _in E _p) of the oscillatory induction period and oscillation period) of the oscillating reaction using thirteen amino acids, leucine (Leu), threonine (Thr), arginine (Arg), lysine (Lys), histidine (His), alanine (Ala), glutamine (Glu), glycine (Gly), methionine (Met), cystine (Cys), tryptophan (Trp), serine (Ser) and tyrosine (Tyr), as organic substrates in amino acid-BrO₃⁻-Mn²⁺-H₂SO₄-acetone system, then based on the Oregonator model and the thermodynamics theory on irreversible process, the thermodynamic function (ΔH _in, ΔG _in, ΔS _in and ΔH _p, ΔG _p, ΔS _p) of these oscillating system are studied. The results indicate the entropy ΔS of these oscillating reaction are negative, thereby it is proved that the oscillating reaction is a noequilibrium system with dissipation structure in agreement with the character of the oscillating reaction from disorder to order in irreversible thermodynamics. These are satisfactorily to explain the experimental phenomena.     

Supramolecular Adduct of γ-Cyclodextrin and [{Re<Subscript>6</Subscript>Q<Subscript>8</Subscript>}(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]<Superscript>2+</Superscript> (Q=S,Se)

Slow evaporation of water solution of [{Re₆S₈}(H₂O)₆]²⁺ generated in situ from [{Re₆S₈}(OH)₆]^4– in presence of γ-cyclodextrin (CD) leads to crystallization of {[{Re₆S₈}(H₂O)₆] ? [γ-CD]}(NO₃)₂·12H₂O (1·12H₂O) supramolecular complex, which was characterized by single-crystal X-ray diffraction crystallography, IR-spectroscopy, thermogravimetric and elemental analyses. X-ray analysis confirms the formation of 1:1 {[{Re₆S₈}(H₂O)₆] ? [γ-CD]}²⁺ inclusion compound in the solid state. However, no adduct formation was detected between [{Re₆S₈}(H₂O)₆]²⁺ and γ-cyclodextrin in solution, according to ¹H NMR spectroscopy. In the case of in situ generated [{Re₆Se₈}(H₂O)₆]²⁺ the reaction solution with γ-cyclodextrin is unstable and during the crystallization only amorphous precipitate has been obtained.     

Influence of ion size on the stability of chloroplumbates containing PbCl<Stack><Subscript>5</Subscript><Superscript>−</Superscript></Stack> or PbCl<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack>

The enthalpies of formation of PbCl₄, PbCl₅⁻ and PbCl₆²⁻, originating from quantum mechanics, have enabled the thermodynamic behaviour of these ions with respect to Cl-detachment to be assessed. The stability of salts containing PbCl₅⁻ and PbCl₆²⁻ as a function of the dimensions of these anions and complementary cations was studied using an approach combining the Kapustinskii-Yatsimirskii equation with basic thermochemical relationships. It was found that hexachloroplumbates of monovalent metal cations will not dissociate into metal chlorides and PbCl₄, provided the complementary cations are suitably large in size. Hexachloroplumbates of divalent metal cations have not yet been synthesised since no known metal cations attain the requisite large size. Such salts will not dissociate if the divalent metal cations are able to complex suitably large electron-donating ligands. The pentachloroplumbates of both monovalent and divalent metal cations are unstable, since no known metal cations have appropriately large ionic radii. The approach adopted appears to be useful for the examination of the thermal behaviour, stability and reactivity of chloroplumbates.     

Synthesis and X-ray diffraction study of Li(H<Subscript>3</Subscript>O)[UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)] · H<Subscript>2</Subscript>O

Single crystals of Li(H₃O)[UO₂(C₂O₄)₂(H₂O)] · H₂O (I) have been synthesized and studied by X-ray diffraction. Compound I crystallizes in the monoclinic crystal system with the unit cell parameters: a = 7.1682(10) Å, b = 29.639(6) Å, c = 6.6770(12) Å, β= 112.3(7)°, space group P 2₁/c, Z = 4, R = 4.36%. Structure I contains discrete mononuclear groups [UO₂(C₂O₄)₂(H₂O)]^2? ascribed to the crystal-chemical group AB ₂ ⁰¹ M¹ (A = UO₂ ²⁺, B⁰¹ =C₂O ₄ ^2? , M¹ = H₂O), which are “cross-linked” by the lithium ions into infinite layers {Li(UO₂)(C₂O₄)₂(H₂O)₂}^? perpendicular to [010]. The hydroxonium ions are located between adjacent uranium-containing layers. A hydrogen bond system involving water molecules, oxalate ions, and hydroxonium combines the anionic layers into a three-dimensional framework.     

Synthesis and structure of cobalt(III) dimethylglyoximate with [FeF<Subscript>5</Subscript>(H<Subscript>2</Subscript>O)]<Superscript>2−</Superscript> anion

A new complex [Co(DH)₂(Thio)₂]₂[FeF₅(H₂O)] · 2CH₃OH (where DH^? is dimethylglyoxime monoanion, Thio is thiourea molecule) was synthesized and its structure was determined. The coordination polyhedron of the Co(III) atoms in two centrosymmetric complex cations is an octahedron, formed by four N atoms of two dimethylglyoxime residues and two S atoms of coordinated Thio molecules. One of the Thio molecules is almost perpendicular to a metal cycle (the dihedral angle 87.8(1)°), which is responsible for realization of intermolecular hydrogen bond N-H···O (N···O 2.990(3) Å). The second Thio molecule is almost parallel to the equatorial CoN₄ fragment (the dihedral angle 159.4(1)°) to give rise to intramolecular π-π interaction between practically planar Thio molecule and one of the π-delocalized metal cycle. The Fe(III) coordination polyhedron is an octahedron, formed by five F atoms and by the O atom of coordinated water molecule. The key role in the crystal structure organization is played by intermolecular hydrogen bonds N-H···F, N-H···O, N-H···S, the intramolecular bonds O-H···O, formed by the donor NH₂ groups of a complex cation with the F atoms of the [FeF₅(H₂O)]^2? and the donor-acceptor groups of the Thio fragments.     

Comparison of the specific adsorption of sulfate (HSO<Subscript>4</Subscript><Superscript>−</Superscript>) ions on Cr and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

The specific adsorption of sulfate ions on powdered Cr was studied by a radiotracer technique using ³⁵S-labeled sulfuric acid in low concentration (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. On the basis of a comparison of the results obtained for Cr₂O₃ and Cr, it can be assumed that, similar to other metals, the overall sorption behavior of Cr is determined by the protective oxide film present on the surface.     

Photochemistry of PtBr<Subscript>6</Subscript><Superscript>2−</Superscript> in aqueous solution

Photochemistry of the PtBr₆ ²⁻ complex in aqueous solution was studied by steady-state and laser flash photolysis (308 nm). The multistep photoaquation of the complex occurs in the nano-and microsecond time intervals without the formation of intermediate platinum(III) complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2277–2283, December, 2007.     

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.     

Crystal Structure of Neptunium(V) Acetate [(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(OOCCH<Subscript>3</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)] ⋅ 2H<Subscript>2</Subscript>O

A new neptunium(V) complex [(NpO₂)₂(CH₃COO)₂(H₂O)] ? 2H₂O was synthesized and its crystal structure was determined. The unit cell parameters are: a = 24.007(10) Å, b = 6.779(3) Å, c = 8.076(3) Å, space group Pnma, Z = 4, V = 1314.2(9) ų, R = 0.049, wR(F²) = 0.105. The crystal structure of the compound is composed of neutral [(NpO₂)₂(CH₃COO)₂(H₂O)] layers and molecules of the water of crystallization. Each of the crystallographically independent neptunoyl ions performs a bidentate function thus forming a composite system of cation-cation bonds.