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.     

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     

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.     

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).     

Yb<Superscript>3+</Superscript> → Er<Superscript>3+</Superscript> energy transfer in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and temperature characteristic of near-infrared photoluminescence

For the Er³⁺–Yb³⁺ codoped Al₂O₃ powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb³⁺ to Er³⁺ was detected by a 978 nm laser diode excitation. Compared with that of Er³⁺ doped Al₂O₃ powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er³⁺–Yb³⁺ codoped Al₂O₃ powders at room temperature. The ET coefficient of 2.18 × 10⁻¹⁸ cm³ s⁻¹ from Yb³⁺ to Er³⁺ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation ⁴I_13/2 → ⁴I_15/2 dominated over thermally enhanced phonon-assisted ET in the Er³⁺–Yb³⁺ codoped Al₂O₃.     

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.     

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.     

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%.     

Analysis of the aromaticity in extended systems formed from isoelectronic Al<Subscript>4</Subscript><Superscript>2−</Superscript> and C<Subscript>4</Subscript><Superscript>2+</Superscript> aromatic clusters

Inspired by carbo-benzene and its inorganic analogues, in the current work, the viability of extended systems (called carbomers) formed from aromatic small rings was studied. The aluminum aromatic cluster, Al₄^2?, and its isoelectronic carbon analogue, C₄²⁺, were employed as starting point. The insertion of alkynyl units into the Al–Al and C–C bonds results in the extended molecules named carbomers. These molecules were compared with the global minima structures, which were searched employing the genetic algorithm program, GEGA. The electronic delocalization (aromaticity) of the isomers was studied with the induced magnetic field (B^ind). The results showed that global minimum of C₁₂²⁺ (formed from C₄²⁺) was an unexpected diatropic structure which presented a similar magnetic response to the C₄²⁺ cluster. Also, optical properties of C₁₂²⁺ were computed.     

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.     

Studies on structure and electrochemical properties of pillared M–MnO<Subscript>2</Subscript> (M=Ba<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, ZrO<Superscript>2+</Superscript>)

Supramolecular pillared oxides were prepared through the intercalation of M²⁺ cations into a MnO₂ host matrix by the method of ion exchange between the precursor δ-K _x MnO₂ and the corresponding guest. The materials M-MnO₂ crystallize in the hexagonal system, the same structure as the precursor, with a larger interlamellar spacing. In the case of ZrO-MnO₂, extended X-ray absorption fine structure (EXAFS) determination indicates that the Zr atom locates between the MnO₂ layers forming a stable structure. Compared with the precursor, the cycling property of M-MnO₂ was improved distinctly, while the capacity decreased to some degree due to the strong interaction between pillars and the host matrix. Among these pillared materials, ZrO-MnO₂ has an advanced reversible capacity of 161.5 mAh·g⁻¹ and improved cycling behavior compared with the precursor.     

Flame synthesized Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> phosphors as spectral convertors for solar cells

Near-infrared (NIR) quantum cutting phosphors serve as a potential material for fabricating photovoltaic spectral convertors. In many cases, quantum cutting phosphors are obtained via a wet chemical method coupled with a post-annealing treatment—a very costly process. In this report, we used continuous flame spray pyrolysis (FSP) for fabricating Y₂O₃:Tb³⁺–Yb³⁺ quantum-cutting phosphors without any post-treatment. Based on characterizations by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we found that as-synthesized Y₂O₃:Tb³⁺–Yb³⁺ phosphors exhibit hollow and shell-like micro-structures composed of highly crystalline and pure cubic-phase nanoparticles (< 50 nm). Photoluminescence studies of the phosphors revealed that NIR emissions appeared with the introduction of Yb to Y₂O₃:Tb³⁺. Phosphor size was successfully controlled by managing the concentration of the metal precursor solution for FSP. The Y₂O₃:Tb³⁺–Yb³⁺ phosphors were then embedded into transparent poly-ethylene-co-vinyl acetate (EVA) film to form a spectral convertor. The composite films of Y₂O₃:Tb³⁺–Yb³⁺ phosphors and poly-EVA were found to be highly transparent in the visible range (> 500 nm), making them suitable as spectral photovoltaic convertors.     

Invar<Superscript>®</Superscript> oxidation in CO<Subscript>2</Subscript>

In this article, corrosion of Invar^® in a static carbon dioxide atmosphere \( 2\times 1 0^{4} \le P_{{{\text{CO}}_{ 2} }} \le 10^{5} \,{\text{Pa}} \) has been studied between 1163 and 1263 K. At the beginning, after a short initial deceleration for weight gains Δm/S <0.5 mg cm^?2, oxidation kinetics were linear up to weight gains of about 4.0 mg cm^?2, and only wüstite Fe_1?x O was formed with a constant rate r (mg cm^?2 s^?1) \( r = \frac{{{\text{d}}\left( {\frac{\Updelta m}{S}} \right)}}{{{\text{d}}t}} = 0.41 \times P_{{{\text{CO}}_{ 2} }} \exp \left( {\frac{ - 198000}{RT}} \right) \) where R is the gas constant and t the time (s). Reaction mechanism is similar to that of the pure iron in analogous conditions, with the same rate limiting step i.e. external reaction of CO₂ with wüstite and outward diffusion of ions Fe²⁺ (not limiting). For weight gains Δm/S higher than 4 mg cm^?2, the limiting step changes, with an increase of the reaction rate and an internal oxidation. The origin of this mechanism change lies in the microcracks appearing in the oxide during its growth. Then, wüstite is no longer bound to the substrate; outward diffusion of ions Fe²⁺ stops and a topotactic transformation converts wüstite into magnetite.     

Sr<Superscript>+</Superscript> + H<Subscript>2</Subscript>O ↔ SrOH<Superscript>+</Superscript> + H equilibrium in flames with strontium admixtures

Sr⁺ + H₂O ↔ SrOH⁺ + H equilibrium was studied spectrophotometrically. This reaction occurs in natural gas combustion products. Its enthalpy Δ_r H ^○(0) = 61.4 ± 2.8 kJ/mol and bond energy D ₀(Sr⁺-OH) = 432.6 ± 2.8 kJ/mol were determined using the third law of thermodynamics. The experimental data on this reaction obtained earlier in hydrogen flames, Δ_r H ^○(0) = 55.3 ± 10.6 and D ₀(Sr⁺-OH) = 438.7 ± 10.6 kJ/mol, were interpreted anew. The D ₀(Sr⁺-OH) = 432.8 ± 2.7 kJ/mol value was eventually obtained.     

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.     

Framework coordination polymer based on the [Re<Subscript>3</Subscript>Mo<Subscript>3</Subscript>S<Subscript>8</Subscript>(CN)<Subscript>6</Subscript>]<Superscript>6–</Superscript>heterometallic cluster anions and Cd<Superscript>2+</Superscript> cations

A new coordination polymer, [Cd(NH₃)₄]₂{Cd[Re₃Mo₃S₈(CN)₆]}·1.5H₂O (I), was prepared by the reaction between solutions of Cd(CH₃COO)₂ · 2H₂O in aqueous ammonia and CaK₄[Re₃Mo₃S₈(CN)₆] · 8H₂O in water. The crystals are cubic, space group Fm3m (Prussian blue structural type); a = 15.0268(4) Å (CIF file CSD no. 431555). According to ESR data, compound I is paramagnetic, g-factor is 2.298. Thermal stability investigation by TGA and powder X-ray diffraction showed that elimination of coordinated NH₃ molecules is accompanied by sample amorphization.     

Blue and green upconversion luminescence modification of Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> co-doped Ca<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F inverse opal

Tb³⁺–Yb³⁺ co-doped Ca₅(PO₄)₃F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant effect on upconversion luminescence of Tb³⁺–Yb³⁺ co-doped Ca₅(PO₄)₃F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap overlapped with the emission band of Tb³⁺ ions.     

Preparation and Characteristics of Nb<Superscript>5+</Superscript>, Ta<Superscript>5+</Superscript>/TiO<Subscript>2</Subscript> Nanoscale Powders by Sol–Gel Process Using TiCl<Subscript>3</Subscript>

Nanoscale TiO₂ powders doping with niobium and tantalum were prepared using TiCl₃ as a source matter. Characterization of the materials was performed by Thermoanalys, particle size, XRD, BET, FTIR, Magnetic Susceptibility. The influence of niobium and tantalum ions on the phase transition was studied, the changes in the crystal size and microstain distributions obtained at 400C were analyzed. The results show that the substitutes of Nb^{5 +}, Ta^{5 +} for Ti⁴⁺ in the anatase structure cause distortions and improve to form rutile. When the dopant content is over certain molar percent, biphase reappears. The IR spectra and magnetic susceptibility indicate the Nb–Nb (or Ta–Ta) bonds along c-axis in rutile by two Nb^{5 +} (Ta^{5 +}) ions located in sites adjacent along the c-axis appear with the dopant content. The magnetic characteristics at rutile showed a weak paramagnetism.     

A computational study on [(PH<Subscript>2</Subscript>X)<Subscript>2</Subscript>]<Superscript>·+</Superscript> homodimers involving intermolecular two-center three-electron bonds

A computational study at CCSD(T) theoretical level has been carried out on radical cation [(PH₂X)₂]^·+ homodimers. Four stable minima configurations have been found for seven substituted phosphine derivatives, X = H, CH₃, CCH, NC, OH, F and Cl. The most stable minimum presents an intermolecular two-center three-electron P···P bond except for X = CCH. The other three minima correspond to an alternative P···P pnicogen bonded complex, to a P···X contact and the last one to the complex resulting from a proton transfer, PH₃X⁺:PHX^·. The complexes obtained have been compared with those of the corresponding neutral ones, (PH₂X)₂, and the analogous protonated ones, PH₃X⁺:PH₂X, recently described in the literature. The spin and charge densities of the complexes have been examined. The electronic characteristics of the complexes have been analyzed with the NBO and AIM methods. The results obtained for the spin density, charge and NBO are coherent for all the complexes.     

Colour tuneability and white light generation in Yb<Superscript>3+</Superscript>–Ho<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript> co-doped SiO<Subscript>2</Subscript>–LaF<Subscript>3</Subscript> nano-glass-ceramics prepared by sol–gel method

Nanostructured transparent glass-ceramics with composition of 95SiO₂–5LaF₃ co-doped with 0.3Yb³⁺, 0.1Ho³⁺ and 0.1Tm³⁺ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron microscopy analysis point out the precipitation of hexagonal LaF₃ nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power.