Complexation of 4′-nitrobenzo-15-crown-5 with Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript> and Ba<Superscript>2+</Superscript> metal cations in acetonitrile-methanol binary solutions

The complex formation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile (AN)-methanol (MeOH) binary mixtures at different temperatures using conductometric method. The results show that 4′-nitrobenzo-15C5 forms 1:1 [ML] complexes with Mg²⁺, Ca²⁺ and Sr²⁺ metal cations in solutions. But in the case of Ba²⁺ cation a 1:2 [ML₂] complex is formed in these solvent systems. The stability of the complexes is sensitive to the solvent composition and a non-linear behavior was observed for variation of logK _f of the complexes versus the composition of the binary mixed solvents. The stability constants of complexes decrease suddenly with increasing the concentration of methanol in this binary system. The values of thermodynamic parameters (ΔH _c^° and ΔS _c^°) for formation of (4′-nitrobenzo-15C5.Mg)²⁺, (4′-nitrobenzo-15C5.Ca)²⁺ and (4′-nitrobenzo-15C5.Sr)²⁺ complexes were obtained from temperature dependence of the stability constants and the results show that these parameters are affected by the nature and composition of the mixed solvents. A non-linear behavior is observed between the ΔS _c^° and the composition of the mixed solvents.     

Intercalation of water and guest molecules within Ca<Superscript>2+</Superscript>–Montmorillonite

The high potential for intercalations by water and various guest molecules is induced by the exchangeable cation inside Ca²⁺–Montmorillonite gallery. XRD peak for Mon at 2θ = 6.04° (d ₀₀₁ = 1.462 nm) shows the structural effect on the clay gallery influenced by the intercalated water layers. Further increases in the gallery height are observed with the intercalation of octadecyl ammonium cations in OMON (d ₀₀₁ = 1.840 nm) and ENR-50 matrix chains in CENR-50 (d ₀₀₁ = 1.954 nm). DSC studies on the other hand reveal the thermal behaviors of intercalated molecules that are linked to the exchangeable cations. The endothermic of Ca²⁺–Montmorillonite (H _Mon = 356.3 J/g) in low temperature range (30–100 °C) indicates the removal of free water and hydrogen bonded water molecules, while the endothermic around 150 °C is related to the induced skeletal layer of water within Ca²⁺–Montmorillonite. The OMON endothermic (H _OMON = 47.0 J/g, T _m = 36.94 °C) tells that cation exchange had modified the water structures and content inside the renewed clay. The intercalation of ENR-50 chains into OMON gallery reveals two endothermic with the T _m1 and T _m2 are at 86.24 and 113.80 °C, respectively. These T _ms confirm that the alkyl chain segment on octadecyl ammonium cation occupy the OMON interlayer space.     

Extractive separation of Cu<Superscript>2+</Superscript>–Co<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript>–Co<Superscript>2+</Superscript> mixtures using <Emphasis Type="Italic">N</Emphasis>-salicylideneaniline

A study on the extraction of copper(II), cobalt(II), and nickel(II) from solutions containing ions of both metals with N-salicylideneaniline(SAN) in chloroform has been realized. Distribution of the metal ions in wide range of pH has been studied. Extraction of copper(II) was always favored over that of cobalt(II). Extraction of copper(II) from binary metal solution is selective and it can be quantitatively separated from cobalt(II). The equilibrium constant of the extraction of cobalt and nickel from an aqueous solution containing both metals using SAN were evaluated. The separation factors for cobalt and nickel were expressed as a function of the distribution of nickel and cobalt. From these results, salicylideneaniline is an adequate extractant for extractive separation of such mixtures.     

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     

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.     

Effects of substituents in the cationic and anionic η<Superscript>3</Superscript>-allylpalladium complexes according to data from <Superscript>13</Superscript>C NMR spectroscopy and quantum chemical calculations

A linear correlation of chemical shifts (δ) of signals in the ¹³C NMR spectra of the unsubstituted terminal carbon atom of the allyl ligand in [(1-R-η³-C₃H₄)Pd]NO₃ (R = Me, CH₂OMe, CO₂Me, COMe, CHO) with the substituent constants σ⁺ and σ^s- in acetone solutions was found. A considerable deviation from linearity was observed for R = Ph. The ¹³C nuclear magnetic screening constants were calculated by the DFT method in the GIAO approximation for equilibrium geometries of the cations [(1-R-η³-C₃H₄)Pd(Me₂C=0)₂]⁺ and anions [(1-R-η³-C₃H₄)PdCl₂]^s-. In the latter case, the theoretical and experimental δ values are consistent. The influence of the substituent R on the geometric parameters and charges on atoms in the neutral, anionic, and cationic η³-allylpalladium complexes is discussed.     

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.     

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.     

Luminescence and long-lasting afterglow in Mn<Superscript>2+</Superscript> and Eu<Superscript>3+</Superscript> co-doped ZnO–GeO<Subscript>2</Subscript> glasses and glass ceramics prepared by sol–gel method

To develop new fluorescent and afterglow materials, Mn²⁺ and Eu³⁺ co-doped ZnO–GeO₂ glasses and glass ceramics were prepared by a sol–gel method and their optical properties were investigated by measuring luminescence, excitation and afterglow spectra, and luminescence quantum yield (QY). Under UV irradiation at 254 nm, some glasses and all of the glass ceramics showed green luminescence peaking at 534 nm due to the ⁴T₁ → ⁶A₁ transition of tetrahedrally coordinated Mn²⁺ ions. The strongest luminescence was observed in a glass ceramic of 0.1MnO–0.3Eu₂O₃–25ZnO–75GeO₂ heat treated at 900 °C, with QY of 49.8%. All of the green-luminescent glasses and glass ceramics showed green afterglow, and the afterglow lasting for more than 60 min was obtained in a glass ceramic heat treated at 900 °C. It is considered that the Eu³⁺ ions may behave as electron trapping centers to be associated with the occurrence of the green afterglow due to the Mn²⁺ ions in the co-doped system.     

Measuring <Superscript>226</Superscript>Ra and <Superscript>232</Superscript>Th activity in soil and vegetation samples using a method of double γ-coincidences

A coincidence method for measuring radium and thorium activity has been developed using the PRIPYAT-2M gamma-ray coincidence spectrometer, with six NaI(Tl) detectors and registration geometry close to 4π. It was tested by measuring soil samples from the Northern region of Montenegro, as well as vegetation samples from the same region. The results showed a good agreement with ones obtained by the HPGe spectrometer.     

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.     

Complexation of 4′-Nitrobenzo-15-crown-5 with Zn<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript>, Cr<Superscript>3+</Superscript> and Sn<Superscript>4+</Superscript> Cations in Acetonitrile–Ethanol Binary Mixtures

The complexation reactions of 4′-nitrobenzo-15-crown-5 (4′NB15C5) with Zn²⁺, Mn²⁺, Cr³⁺ and Sn⁴⁺ cations were studied in acetonitrile–ethanol (AN–EtOH) binary solvent mixtures at different temperatures by the electrical conductometry method. The stability constants of the resulting 1:1 complexes were determined from computer fitting of the conductance versus mole ratio data. The results show that the selectivity order of 4′NB15C5 for the metal cations in the AN–EtOH (mol-%AN=76) binary solvent at 298.15 K is: Cr³⁺>Mn²⁺≈Zn²⁺>Sn⁴⁺, but the selectivity order changes with the composition of the mixed solvents. A nonlinear relationship was observed between the stability constants (log ₁₀ K _f) of these complexes and the composition of the AN–EtOH binary solvents. The corresponding thermodynamic parameters (DH_c^o, DS_c^o)(\Delta H_{\mathrm{c}}^{\mathrm{o}}, \Delta S_{\mathrm{c}}^{\mathrm{o}}) were obtained from the temperature dependence of the stability constants using van’t Hoff plots. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.     

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.     

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.     

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.     

Magnetic study of a cyano-bridged bimetallic complex with Cu<Superscript>2+</Superscript> macrocycle and [Fe(CN)<Subscript>6</Subscript>]<Superscript>3−</Superscript> ions as building blocks

A new bimetallic cyano-bridged complex, based on copper(II) macrocycle and hexacyanoiron(III) as building blocks, [CuL(H₂O)₂]{[CuL][Fe(CN)₆] · 2H₂O} (1) (L = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.18,11]-octadecane) has been synthesized and magnetically characterized. Make a study of magnetic using a chain model which takes into account of monomeric impurity confirm showing an antiferromagnetic coupling in paramagnetic ions with J = −0.170 cm⁻¹ and 3.56 % impurity.     

Synthesis and crystal structure of a cyanide-bridged one-dimensional nickel(II) complex with alternating [Ni(En)<Superscript>2</Superscript>]<Superscript>2+</Superscript> and [Ni(CN)<Subscript>4</Subscript>]<Superscript>2−</Superscript> ions

The complex [Ni(En)₂][Ni(CN)₄] · 3.5H₂O (I) (En = ethylenediamine) was synthesized by the reaction of [Ni(En)₂](ClO₄)₂ and K₂[Ni(CN)₄] in an H-shaped tube. The crystal structure of I has been determined by single-crystal X-ray analysis. The crystal of complex I is orthorhombic, space group Pnna with a = 28.151(3), b = 8.3946(8), c = 14.5441(13)Å, M =404.76, Z = 8, V = 3437.0(5)ų. The structure of complex I reveals infinite zigzag chains shaped structure are formed by cis-Ni(En)₂-μ-(NC)₂, cis-μ-(NC)₂Ni(CN)₂, and trans-μ-(CN)₂Ni(En)₂.     

Comparison of sorption of Pb<Superscript>2+</Superscript> and Cd<Superscript>2+</Superscript> on Kaolinite clay and polyvinyl alcohol-modified Kaolinite clay

Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with polyvinyl alcohol (PVA) reagent to obtain PVA-modified Kaolinite clay adsorbent. Scanning Electron Microscopy (SEM) of the PVA-modified adsorbent suggests that Kaolinite clay particles were made more compact in nature with no definite structure. Modification of Kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb²⁺ and Cd²⁺ by a factor of at least 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb²⁺ and Cd²⁺ decreased the adsorption capacity of Unmodified Kaolinite clay for Pb²⁺ by 26.3% and for Cd²⁺ by 0.07%, respectively. In contrast, for PVA-modified Kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb²⁺ and Cd²⁺, respectively. The adsorption data of Pb²⁺ and Cd²⁺ onto both Unmodified and PVA-modified Kaolinite clay adsorbents were found to fit the Pseudo-Second Order Kinetic model (PSOM), indicating that adsorption on both surfaces was mainly by chemisorption and is concentration dependent. However, kinetic adsorption data from both adsorbent generally failed the Pseudo-First order Kinetic model (PFOM) test. Extents of desorption of 91% Pb²⁺ and 94% Cd²⁺ were obtained, using 0.1 M HCl, for the Unmodified Kaolinite clay adsorbent. It was found that 99% Pb²⁺ and 97% Cd²⁺, were desorbed, for PVA-modified Kaolinite clay adsorbents within 3 min for 60 mg/L of the metal ions adsorbed by the adsorbents.     

A simple and quick method for the preparation of radionuclide <Superscript>87</Superscript>Y/<Superscript>87m</Superscript>Sr generator using the <Superscript>nat</Superscript>Rb(α,xn)<Superscript>87</Superscript>Y reaction

A rapid method for the preparation of ⁸⁷Y/^87mSr radionuclide generator from a rubidium chloride target irradiated with 35 MeV α-particles is described. A simple two-step procedure is used to obtain a carrier-free ^87mSr isotope with a high enough radiochemical yield and high purity in the final aqueous fraction.     

Spectrophotometric study of Eu<Superscript>+</Superscript> + H<Subscript>2</Subscript>O ↔ EuOH<Superscript>+</Superscript> + H equilibrium in flames with europium additions

Using the third law of thermodynamics, we found the enthalpy Δ_r H ^o(0) = 71 ± 7 of the reaction Eu⁺ + H₂O ↔ EuOH⁺ + H and the binding energies D ₀(Eu⁺-OH) = 423 ± 7 and D ₀(Eu-OH) = 389 ± 11 (kJ/mol). To determine the latter, we additionally used the ionization potential I ₀(EuOH) = 5.32 ± 0.08 eV found using the Stark intramolecular effect.