Isopiestic determination of the osmotic and activity coefficients of aqueous Lu2(SO4)3 at 25°C

Osmotic coefficients have been measured for aqueous Lu₂(SO₄)₃ solutions from 0.12402 to 0.89631 mol-kg^–1 at 25°C by use of the isopiestic method; these measurements extend into the supersaturated molality region. Since there was a lack of activity data for Lu₂(SO₄)₃ solutions at lower molalities, they were approximated by equating them to results for La₂(SO₄)₃ from freezing temperature depression measurements. The combined osmotic coefficients were then used to derive mean molal activity coefficients for Lu₂(SO₄)₃ solutions. The osmotic coefficients decrease to 0.307 as their minimum value and the mean molal activity coefficients decrease to 0.0069. When these activities were combined with our previously reported solubility of 0.6260±0.0017 mol-kg^–1 for Lu₂(SO₄)₃·8H₂O, a thermodynamic solubility product of 2.3×10^–10 was obtained. This value yields the Gibbs energy of formation G _f ^° (Lu₂(SO₄)₃·8H₂O, cr)=–5518.9±16.4 kJ-mol^–1.     

Characteristic lengths and the structure of salt free polyelectrolyte solutions. A small angle neutron scattering study

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS ₁(q) and the structure factorS ₂(q). Two lengths are deduced from these two factors: the persistence lengthb _t which characterizes the electrostatic interactions along the chain by a fitting ofS ₁(q) with calculation of the scattering function for a wormlike chain, and fromS ₂(q),q _m ^–1 which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b _t C _p ^–1/2 ,q _m ^–1 C _p ^–1/2 ) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS.     

Crystal structure of [Cu4(pytp)2(SO4)2(H2O)10](SO4)2 · 4H2O. A tetranuclear copper(II) complex with a new asymmetric ligand,pytp*, as a bridge

A new asymmetric bridge ligand, pytp, was prepared and characterized systematically by f.t.i.r., u.v.–vis., ¹H-n.m.r. and by FAB-MS spectroscopy. A tetranuclear Cu^II complex [Cu₄(pytp)₂(SO₄)₂(H₂O)₁₀](SO₄)₂·4H₂O (1) was prepared and characterized by elemental analysis and u.v.–vis. spectroscopy. A crystal structure analysis indicates that there are two different coordination spheres in (1) and that two of the copper centers are bridged by two ₂-SO₄ entities, creating a most unusual sulphate bridge.     

Structure of Electrical Double Layer on Liquid Pb–Ga Alloy in Aqueous Electrolytes

A new electrode, which is a liquid Pb–Ga alloy (0.06 at. % Pb), is developed and studied. It is shown that the alloy's double-layer characteristics dramatically differ from characteristics of a Ga electrode and are practically identical to characteristics of a Pb electrode. Hence, the Pb–Ga electrode in fact models electrochemical properties of a liquid Pb electrode. It is established that the metallic capacitance of the Pb–Ga electrode occupies an intermediate position between values of metallic capacitance of Ga and Hg electrodes, provided the metal–water chemisorption interaction is absent and the electrode charge is fixed. Hydrophilicity of the Pb–Ga electrode is substantially lower than hydrophilicity of a Ga electrode and coincides with hydrophilicity of an Hg electrode. It is shown that In–Ga, Cd–Ga, and Pb–Ga electrodes have close values of the electrochemical work function, and the chemisorption potential drop of the solvent in them increases in the series Pb–Ga < In–Ga < Cd–Ga with decreasing distance of closest approach of water molecules to the ionic core of the metal. The absorbability of anions at the Pb–Ga electrode increases in the series BF^– ₄= SO^2– ₄< Cl^–< Br^–< I^–.     

Isothermal reduction of barite with hydrogen

The reduction of barite concentrate with hydrogen was studied by using a Shimadzu 31 H Thermoanalyser coupled with a gas-feeding system and a Uras 7 N infrared SO₂ gasanalyser made by Hartman Brown Co. The kinetic parameters were determined by means of a computer program on the basis of the thermogravimetric curves in the temperature range 1098–1223 K. The experimental data obey the contracting volume kinetic equationkt=1–(1–)^1/3.

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Zusammenfassung Mittels eines Shimadzu 31 H Thermoanalysators, ausgerüstet mit einem Gasspeisungssystem und einem von Hartman Brown Co hergestellten Uras 7 N Infrarot-SO₂-Gasanalysator, wurde die Reduktion von Bariumkonzentrat mit Wasserstoff untersucht. Auf der Basis der TG-Daten im Bereich 1098–1223 K wurden unter Zuhilfenahme eines Computerprogrammes die kinetischen Parameter ermittelt. Die experimentellen Daten folgen einer kinetischen Gleichung der Formkt=1–(1–)^1/3.

     

Reaction of Ru(PPh3)3Cl2 with arylazoimidazoles: spectral characterisation and redox studies of [bis-{N(1)-alkyl-2-(arylazo)imidazole}-bis-(triphenylphosphine)]-ruthenium(II) perchlorate

Ru(PPh₃)₃Cl₂ reacts with N(1)-alkyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂N₂X, [RaaiX, R = H(a), Me(b), Cl(c); X = Me(1), Et(2), Bz(3)] under refluxing conditions in EtOH to give [Ru(RaaiX)₂(PPh₃)₂](ClO₄)₂ · H₂O complexes (4–6). RaaiX is a bidentate chelator (N, N) with N(imidazole), N and N(azo), N donor centres. Three isomers are present in the mixture in which the pairs of PPh₃, N and N occupy cis–cis–trans, cis–trans–cis and cis–cis–cis, positions respectively. The isomers were identified by ¹H-n.m.r. spectra. Four signals are observed in the aliphatic zone for N(1)-X; two are of equal intensity at higher and the other two signals at lower in the ratio 1:0.3:0.2 suggesting the presence of cis–cis–cis, cis–trans–cis and cis–cis–trans-geometry. The complexes display the allowed t ₂(Ru) ^*(RaaiX) transition. Cyclic voltammetry indicates two consecutive Ru^III/II couples along with azo reductions.     

Unusually facile syntheses of [RuII(bpy)3]2+ (bpy = 2,2′-bipyridine) and [RuII(phen)3]2+ (phen = 1,10-phenanthroline)

The salts [Ru^II(L–L)₃](CF₃SO₃)₂ (L–L = bpy or phen) have been prepared in high yields via reactions of [Ru^II(DMF)₆](CF₃SO₃)₂ (DMF = N,N-dimethylformamide), generated in situ by reduction of [Ru^III(DMF)₆]-(CF₃SO₃)₃, with an excess of bpy or phen at room temperature in DMF solutions.     

Heterotri- and -tetrametallic alkoxides of chromium(III) containing aluminium(III), gallium(III) and niobium(V)

CrCl₃ · 3THF reacts with two equivalents of potassium alkoxometallates K{M(OPr ⁱ ) _x } [M = Al(A), Ga(B), x = 4; M = Nb(C), x = 6] to give heterobimetallic chloride isopropoxides [Cr{M(OPr ⁱ ) _x }₂Cl(THF)] [M = Al(A – 1), Ga(B – 1), and Nb(C – 1)], in which the replacement of the chloride with an appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) results in the formation of novel heterotrimetallic derivatives. The 'single pot synthesis of an heterotetrametallic isopropoxide [Cr{Nb(OPr ⁱ )₆}{Al(OPr ⁱ )₄}{Ga(OPr ⁱ )₄}] (7) has been carried out by the sequential addition of (A), (B), and (C) to a benzene suspension of CrCl₃ · 3THF. Alcoholysis of [Cr{Al(OPr ⁱ )₄}₂{Nb(OPr ⁱ )₆}] (1) and [Cr{Al(OPr ⁱ )₄}₂{Ga(OPr ⁱ )₄}] (5) with t-BuOH has also been studied and the derivatives characterized by elemental analyses, molecular weight determinations, spectroscopic [Electronic, i.r., ²⁷Al-n.m.r.] and magnetic susceptibility studies.     

Synthesis,characterization and charge-transfer photochemistry of trans-aquo azido-N,N′-trimethylenebis(naphthylideneiminato)chromium(III)

A new Cr^III complex, viz. trans-[Cr(naphprn)(H₂O)₂]ClO₄·2H₂O, (1) {naphprn=N,N-trimethylenebis(naphthylideneimine)} has been synthesized and characterized. Aquo ligand substitution of ( 1 ) by the azide ligand gave rise to trans-[Cr(naphprn)(N₃)(H₂O)], ( 2 ). Irradiation of ( 2) in DMF gave nitrido(naphprn)chromium(V) ( 3 ). Solutions of ( 3 ) showed e.p.r. spectra at room temperature (g _iso=1.9865). The i.r. spectra showed disappearance of a band at 2067cm^–1 showing the breakdown of NN and appearance of a new band at 1074cm^–1which is assigned to the Cr¹⁴N, stretching frequency indicating the formation of a nitrido chromium(V) complex, ( 3). The u.v.–vis. spectrum of complex ( 3 ) exhibited a d–d band maximum at 553nm (=120M^–1cm^–1). The rate of formation of ( 2 ) was found to be 5.0×10^–3M^–1s^–1 in an aqueous acidic medium at [Cr^III]=0.5×10^–3M; [N₃ ^–]=0.01–0.15M; [H⁺]=0.001M and I=0.2M (LiClO₄). The rate of photo-decomposition of ( 2 ) to give rise to ( 3 ) was found to be 0.15×10^–3s^–1 in DMF.     

Analysis of experimental data on the EDL capacitance for different metals in asymmetrical electrolytes: Accounting for the solution nonideality

Potential dependences of differential capacitanceC are measured in diluted aqueous La₂(SO₄)₃ solutions on Hg, Tl-Ga, and Cd-Ga electrodes and in aqueous Na₂SO₄ solutions on the Cd-Ga electrode. The 1/C vs. 1/C_d dependences (where C_d is the differential capacitance of the diffuse layer) are linear and have a unit slope at the potential of zero charge, provided C_d is calculated using the Gonzalez-Sanz theory. Calculations based on the Gouy-Chapman-Grahame theory yield inadequate results.     

Nonlinear Impedance of Liquid In–Ga Electrode in Aqueous Solutions of a Symmetrical Surface-Inactive Electrolyte

Experimental data related to the potential dependence of nonlinear characteristics of the electrical double layer at a liquid In–Ga electrode in aqueous solutions of a symmetrical surface-inactive electrolyte are obtained for the first time. It is shown that, as opposed to polycrystalline Cd and Pb electrodes, on a liquid (atomically smooth) In–Ga electrode, as on Hg, there is a clear intersection of the potential dependences of a nonlinear signal for different concentrations of a 1–1-valence surface-inactive electrolyte at one point. The intersection point exactly corresponds to the potential of zero charge of an electrode undistorted by specific adsorption of ions. It is established that, when estimating hydrophilicity of metals by a nonlinear impedance method, most information is provided by the region of average negative charges, rather than by the region near zero charge. It is shown that, as opposed to a linear impedance method, the nonlinear impedance method makes it possible to determine, directly from experiment, quantities that directly characterize the metal–solvent chemisorption interaction in a pure form; at the same time, these quantities are criteria of lyophilic nature of metals. Quantities that characterize the metal–solvent chemisorption interaction, obtained by the linear and nonlinear impedance methods are in good agreement, which confirms the validity of the approach we proposed earlier for separating the difference between reciprocal capacitances of the inner part of the electrical double layer on Hg and metal M, ^Hg _M C ^-1 _i= 1/C ^Hg _i– 1/C ^M _iinto physical (^Hg _M C ^–1)_physand chemical constituents. This coincidence also confirms correctness of numerical values obtained earlier for quantities (^Hg _M C ^–1)_phys.     

Verfeinerung der Kristallstruktur von Te2O3(SO4)

The crystal structure of ditellurium(IV)-trioxide sulfate, Te₂O₃(SO₄)—space group Pmn2₁–C _2v ⁷ ;a=8.879 (2),b=6.936 (2),c=4.646 (4) Å,Z=2—has been determined and refined by least-squares, using three-dimensionalX-ray data (1188 independent reflexions) to a final R-value of 6.3%.The crystal structure comprises puckered tellurium(IV)—oxygen layers in which the tellurium atoms are linked together by three oxygen bridges (Te–O 1.907, 1.945, 2.011 Å). The SO₄ groups are arranged between these layers. Two oxygen atoms of each SO₄ group are bonded to two adjacent tellurium atoms of one layer [Te–O(S) 2.270 Å] and the tellurium atoms show a (3+1) coordination. A third oxygen atom of the SO₄ group is in weak interaction with two adjacent tellurium atoms of the same layer (Te–O 2.603 Å) whereas the fourth oxygen atom has distances of 2.866 Å to two adjacent tellurium atoms of the next layer and effects a very weak interaction between the

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Mit 3 Abbildungen

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Herrn Prof. Dr.R. Kieffer zu seinem 70. Geburtstag gewidmet.     

Synthesis,spectroscopic, photophysical and electrochemical behaviour of ruthenium(II) and copper(I) isocyano-bridged complexes with polypyridine ligands: 2,2′-bipyridine and 1,10-phenanthroline

New binuclear complexes with [Cu(PPh₃)₃]⁺ and [Cu(PPh₃)(N—N)]⁺ (N—N – 2,2-bipyridine, 1,10-phenanthroline) moieties connected via the isocyanide group to [Ru(bpy)₂(py)]⁺ and [Ru(phen)₂(py)]⁺ have been prepared and isolated as PF₆ ^– salts. In addition, new trinuclear complexes, [{(PPh₃)₃Cu(-NC)}₂Ru(bpy)₂](PF₆)₂ and [{(N—N)-(PPh₃)Cu(-NC)}₂Ru(bpy)₂](PF₆)₂, have been synthesized using [Ru(bpy)₂(CN)₂]. The complexes have been characterized by elemental analyses, i.r., n.m.r., u.v.–vis., FAB mass spectra and by conductivity measurements. The i.r. spectra reveal an increase in v;(CN) in the isocyano-bridged complexes compared to the mononuclear parent complexes. The complexes are luminescent with emission wavelengths in the 458–550 and 600–636 nm ranges. The half wave reduction potentials in MeCN are always more positive than those of the parent complexes. It is observed that the isocyano-bridged complexes are more powerful excited state reductants than the cyano-bridged, Cu^(I)(-CN)Ru^(II) complexes.     

Tensimetric investigation of the CrCl<Subscript>3</Subscript>—Cl<Subscript>2</Subscript> system in the temperature range of 600–1200 K

The sublimation pressure of chromium trichloride was measured by the static method with a quartz membrane-gauge manometer in the temperature range of 875–1230 K. An approximating equation for the sublimation pressure vs. temperature was found. The enthalpy (259.4±4 kJ mol^–1) and the entropy (224.2±3.5 J mol^–1 K^–1) of sublimation at 298 K were calculated. For the process 2 CrCl₃(g) + Cl₂(g) = 2 CrCl₄(g), the following values were obtained: _r H°₂₉₈ = –207.1±11.6 kJ mol^–1 and _r S°₂₉₈ = –173.6±10 5 J mol^–1 K^–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1561–1564, August, 2004.     

Iron Catalysis of SO2 Oxidation in the Atmosphere

The mechanisms of SO₂ oxidation catalyzed by iron ions in the droplet phase of the convective cloud in the lower atmosphere were examined. The relations of the catalytic SO₂ decrease to the concentration of the iron ions and to the intensity of fluxes to the droplet of the OH _(g) and HO _2(g) radicals were characterized. The determining role of the replacement of the low-reactive HO _2(g)(O^– _2(aq)) radical by the reactive SO^– _5(aq) radical in the sulfite medium during daytime was revealed. This process occurred due to the coupling of the decay of the radicals and their regeneration in the liquid-phase reactions O^– _2(aq) + FeOH²⁺ _(aq) Fe²⁺ _(aq) + OH^– _(aq) + O_2(aq), HSO^– _5(aq) + Fe²⁺ _(aq) FeOH²⁺ _(aq) + SO^– _4(aq)HSO ₃ ^- _(aq),O_{2 (aq)} SO^– _5(aq).     

Crystal structure of the La3+ sandwich complex based on 8-membered macrocyclic siloxanolate ligands

The product of the reaction between anhydrous lanthanum trichloride and potassium vinylsiloxanolate, K₅[VinSiO₂]₈La₄(₄-OH)[O₂SiVin]₈ · 5n-BuOH·2H₂O has been studied by X-ray diffraction. The compound is a «sandwich»-type complex where macrocyclic vinyloctasiloxanolate ligands with regularcis-configuration have co-axial and antiparallel orientation. These ligands coordinate a planar «cationic layer» formed by four La³⁺ ions and stabilized by an additional ₄-OH^– bridge ligand. A three-dimensional cage structure of complex lanthansiloxanolate pentaanions linked through the coordinated K⁺ counter-ions is formed in the crystal studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 184–189, January, 1993.     

Ions in Aqueous Acetic Acid Mixtures: Solvent Reorganization around Protons and Gibbs Energies of Transfer from Water

The photo-absorbing, basic sensor, 4-nitroaniline, has been used to determine theequilibrium constant for solvent reorganization around the proton in mixtures ofvarying composition of water with acetic acid. In all the mixtures used, theself-ionization of the acetic acid was suppressed. In contrast to mixtures of waterwith the related ethanol or acetone, this equilibrium is shifted more toward thewater-solvated species as the mole fraction x ₂ of the cosolvent increases. TheGibbs energy of transfer of protons from water into the mixture G ^o _t (H⁺) can bederived with the aid of this equilibrium constant for the solvent reorganization.Using G ^o _t (H⁺), G ^o _t (i) for i denoting anions and other cations can be evaluated.In comparison the G ^o _t (i) for cations have lower negative values than when eitherethanol or acetone is added to water. Correspondingly, for halide anions, thepositive G ^o _t (i) with added acetic acid are rather less than is found with eitherethanol or acetone added. The influence on the ion-solvent interaction of bothelectron withdrawing hydroxy and carbonyl groups in acetic acid may beresponsible for this. Although G ^o _t (i) for C10^– ₄ and Re0^– ₄ are also positive, both picrateions and OH^– give negative values with acetic acid added to water. With picrateions, the hydrophobic effect of the carbon ring produces stabilization in themixture relative to water. With OH^–, complete conversion to acetate anionsoccurs. As is found with other cosolvents, the contribution of the charge onacetate anion to G ^o _t (CH₃COO^–) is found to increase as x ₂ rises. The aciddissociation constant K _a for acetic acid is found to decrease slowly as x ₂ rises to0.5, followed by a rapid decrease for x ₂ greater than 0.7 where dimerization ofacetic acid occurs.     

The double salts M3RE(SO4)3 (M=K,Rb) with framework structures

The crystal structures of K₃Er(SO₄)₃ [space group Pc, a=9.222(2), b=14.688(1), c=9.008(1) Å, =110.72(2)^o, Z=4, R=0.59] and of Rb₃Tm(SO₄)₃ [space group Cc, a=10.649(2), b=15.149(3), c=9.320(2) Å, =124.49(1)^o, Z=4, R=0.043] have been studied (CAD-4 diffractometer, Mo radiation). It has been shown that the compounds K₃RE(SO₄)₃ (RE=Nd–Er) and Rb₃RE(SO₄)₃ (RE=Tm–Lu), which crystallize in accordance with these structural types, form a family of framework structures with a single basis. The relationship between their structure and the structure of the rhombohedral compounds M₃M^III(SO₄)₃ (M^III=Al, Ga, In) and Cs₃Yb(SO₄)₃ has been examined.Scientific-Research Institute of Chemical Reagents and Ultrapure Chemical Substances. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 110–115, March–April, 1991.     

Adsorption of Cl? ions on electrodeposited rhodium black layer (rhodized electrode) at low concentrations

The adsorption of Cl^– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl^– ion concentrations (c10^–5 mol dm^–3) in 1 mol dm^–3 H₂SO₄ supporting electrolyte. The specific adsorption of Cl^– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined.     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.