Complexation of 4′-nitrobenzo-15-crown-5 with Li+, Na+, K+, and NH 4 + cations in acetonitrile–methanol binary solutions

The complexation processes between Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile–methanol (AN–MeOH) binary mixtures at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complexes formed between the ligand and Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations is 1:1(M:L). Addition of 4′-nitrobenzo-15C5 to these cations solution, causes a continuous increase in the molar conductivities which indicates that the mobility of the complexed cations is more than the uncomplexed ones. The values of stability constants of the complexes were determined from conductometric data using GENPLOT computer program. The obtained results show that the selectivity order of the ligand for Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations changes with the nature and composition of the binary mixed solvent. The values of thermodynamic parameters (ΔH°_c, ΔS°_c) for formation of the complexes were obtained from temperature dependence of the stability constants using the van’t Hoff plot. The results show that the complexes are both enthalpy and entropy stabilized. A non-linear behavior was observed between the stability constants (log K _f ) of the complexes and the composition of the AN–MeOH binary solution.     

Thermodynamic behavior of complexation process between benzo-15-crown-5 with Li+, Na+, K+, and NH4 + cations in acetonitrile–methanol binary media

The stability constants of 1:1 (M:L) complexes of benzo-15-crown-5 (B15C5) with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations, the Gibbs standard free energies ( $ \Updelta {\text{G}}_{\text{c}}^{ \circ } $ ), the standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) and standard entropy changes ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) for formation of these complexes in acetonitrile–methanol (AN–MeOH) binary mixtures have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and the studied cations is 1:1 (M:L). In most cases, addition of B15C5 to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The results show that the selectivity order of B15C5 for the metal cations changes with the nature and composition of the binary mixed solvent. The values of standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) were calculated from the relationship $ \Updelta {\text{G}}_{{{\text{c}},298.15}}^{ \circ } = \Updelta {\text{H}}_{\text{c}}^{ \circ } - 298.15\Updelta {\text{S}}_{\text{c}}^{ \circ } $ . A non-linear behavior was observed between the stability constants (log K_f) of the complexes and the composition of the acetonitrile–methanol (AN–MeOH) binary solution. The results obtained in this study, show that in most cases, the complexes formed between B15C5 and Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations are both enthalpy and entropy stabilized and the values of these thermodynamic quantities change with the composition of the binary solution.     

Interaction of salts in ionic melts of the ternary reciprocal systems Na,K‖BO2,MoO4 and Na,K‖BO2,WO4

The phase diagrams of the ternary reciprocal systems Na,K‖BO₂,MoO₄ and Na,K‖BO₂,WO₄ were studied for the first time by a calculation-experimental method and differential thermal analysis. The coordinates were determined for binary eutectics of the diagonal stable sections NaBO₂-K₂MoO₄(K₂WO₄) and the ternary invariant points e(55 mol % NaBO₂, 45 mol % K₂MoO₄, 740°C), e(55 mol % NaBO₂, 45 mol % K₂WO₄, 730°C), E(4.5 mol % NaBO₂, 78 mol % Na₂MoO₄, 17.5 mol % K₂MoO₄, 652°C), E(4.5 mol % NaBO₂, 78 mol % Na₂WO₄, 17.5 mol % K₂WO₄, 643°C), P₂(5 mol % NaBO₂, 56 mol % Na₂MoO₄, 39 mol % K₂MoO₄, 673°C), P₂(5 mol % NaBO₂, 56 mol % Na₂WO₄, 39 mol % K₂WO₄, 671°C). Binary solid solutions based on sodium and potassium metaborates were shown to be stable. Analytical models of phase equilibrium states of the ternary reciprocal systems Na,K‖BO₂,MoO₄(WO₄) were obtained, which enable one to calculate melting (crystallization) points and construct isotherms at any given composition. The specific heats of melting of samples of invariant compositions were found by quantitative differential thermal analysis.     

Conductometric studies of the thermodynamics complexation of Li+, Na+, K+, Mg2+, and Ba2+ ions with 4′,4″(5″)-Di-tert-butyldibenzo-18-crown-6 ligand in acetonitrile, ethanol and methanol solutions

The complexation reaction between 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6, ligand and Li⁺, Na⁺, K⁺, Mg²⁺, and Ba²⁺ ions were studied conductometrically in acetonitrile, ethanol, and methanol solutions. The formation constants of the 1:1 and 2:1 complexes (metal to ligand) were calculated from the computer fitting of the molar conductance in various mole ratios at 10, 20, 30, and 40 °C. The enthalpy and entropy changes of the complexation reactions in acetonitrile, ethanol, and methanol were estimated at four different temperatures.     

Synthesis and chemical behavior of the inorganic cryptates (MSb9W21O86)(19−n)− Mn+  Na+, K+, NH4+, Ca2+, Sr2+

The synthesis and the chemical behavior of the polyanionic ligand Sb₉W₂₁O₈₆¹⁹⁻ were studied: two types of coordination sites were evidenced and their reactivity discussed with regard to the polytungstic structure.     

Naphthalene and pyrrole substituted guanidine in selective sensing of Cu2+, Hg2+, Pb2+ and CN− ions under different conditions

Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu²⁺, Hg²⁺ and Pb²⁺ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg²⁺ and Pb²⁺ ions in CH₃CN and CH₃CN–H₂O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu²⁺ ion in CH₃CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN^? ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction.     

Bingel–Hirsch Addition of Diethyl Bromomalonate to Ion-Encapsulated Fullerenes M@C60 (M=Ø, Li+, Na+, K+, Mg2+, Ca2+, and Cl−)

In the last 30 years, fullerene-based materials have become popular building blocks for devices with a broad range of applications. Among fullerene derivatives, endohedral metallofullerenes (EMFs, M@C_x) have been widely studied owing to their unique properties and reactivity. For real applications, fullerenes and EMFs must be exohedrally functionalized. It has been shown that encapsulated metal cations facilitate the Diels–Alder reaction in fullerenes. Herein, the Bingel–Hirsch (BH) addition of ethyl bromomalonate over a series of ion-encapsulated M@C₆₀ (M=Ø, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cl⁻; Ø@C₆₀ stands for C₆₀ without any endohedral metal) is quantum mechanically explored to analyze the effect of these ions on the BH addition. The results show that the incarcerated ion has a very important effect on the kinetics and thermodynamics of this reaction. Among the systems studied, K⁺@C₆₀ is the one that leads to the fastest BH reaction, whereas the slowest reaction is given by Cl⁻@C₆₀.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Ba2Ca2Cu3Ox Precursor Effects on Synthesis of (Hg,Pb)Ba2Ca2Cu3O8+δ Superconductor

The influence of Ba₂Ca₂Cu₃O_x precursor on the synthesis and properties of (Hg,Pb)Ba₂Ca₂Cu₃O_8+δ has been examined. Fine homogeneous Hg-free precursor powder of Ba₂Ca₂Cu₃O_x of desirable phase composition was prepared by sol-gel method using EDTA acid as a complexing agent. A reproducible superconducting sample of Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+δ with fine-grained, dense microstructure, composed predominantly of (Hg,Pb)-1223 phase and with advantageous magnetic properties, was synthesized by high pressure crystallization in mercury environment of well-calcined Ba₂Ca₂Cu₃O_x precursor. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differentiation of the Na,K,Ca,Ba‖F,WO4 multicomponent system and phase equilibria in its stable secant complex NaF-K2WO4-CaF2-BaF2

The Na,K,Ca,Ba‖F,WO₄ quinary mutual system was differentiated based on graph theory with consideration of identified internal secant elements using a program complex. For the first time, by a combination of physicochemical analysis methods (differential thermal, visual polythermal, X-ray diffraction and projection-thermal-analytical), the NaF-K₂WO₄-CaF₂-BaF₂ quaternary system was studied, which is a stable secant complex of the quinary mutual system. The coordinates of invariant points were determined.     

Structures, energetics, and aromaticities of the tetrasilacyclobutadiene dianion and related compounds: (Si4H4)(2-), (Si4H4)(2-)·2Li+, [Si4(SiH3)4](2-)·2Li+, [Si4(SiH3)4](2-)·2Na+, and [Si4(SiH3)4](2-)·2K+

In light of the important recent synthesis of a stable tetrasilacyclobutadiene dianion compound by Sekiguchi and co-workers and the absence of theoretical studies, ab initio methods have been used to investigate this dianion and a number of related species. These theoretical methods predict multiple minima for each compound, and most minima contain folded and bicyclic silicon rings. For (Si(4)H(4))(2-), (Si(4)H(4))(2-)·2Li(+), [Si(4)(SiH(3))(4)](2-)·2Li(+), [Si(4)(SiH(3))(4)](2-)·2Na(+), and [Si(4)(SiH(3))(4)](2-)·2K(+), respectively, the energetically lowest-lying structures are designated A-3 (C(2v) symmetry), B-8 (C(1) symmetry), C-1 (C(2) symmetry), D-1 (C(2) symmetry), and E-1 (C(2h) symmetry). None of these structures satisfies both the ring planarity and the cyclic bond equalization criteria of aromaticity. However, all of the representative NICS values of these lowest-lying structures are negative, indicating some aromatic character. Especially, structures C-1 and D-1 of C(2) symmetry effectively satisfy the criteria of aromaticity due to the slightly trapezoidal silicon rings, which are nearly planar with nearly equal bond lengths. SiH(3) substitution for hydrogen in (Si(4)H(4))(2-)·2Li(+) significantly reduces the degree of aromaticity, as reflected in the substantially smaller NICS absolute values for [Si(4)(SiH(3))(4)](2-)·2Li(+) than those of (Si(4)H(4))(2-) and (Si(4)H(4))(2-)·2Li(+). The aromaticity is further weakened in [Si(4)(SiH(3))(4)](2-)·2Na(+) and [Si(4)(SiH(3))(4)](2-)·2K(+) by replacing lithium with the sodium and potassium cations.     

Mechanism of simultaneous removal of Ca2+, Ni2+, Pb2+ and Al3+ ions from aqueous solutions using Purolite® S930 ion exchange resin

The sorption mechanism of Ca²⁺, Ni²⁺, Pb²⁺, and Al³⁺on ion exchange resin S930 has been studied as a function of pH in both mono-component and quaternary systems at ion ratio 1:1:1:1. The equilibrium of ion exchange process in mono-component systems has been followed as an adsorption process and it was tested for Langmuir and Freundlich isotherm equations. The selectivity coefficient of the resin for these cations varied in different manners depending on the pH range. The structural characteristics of pores in the initial resin and the resin after contact with synthetic solutions at pH 3.03 and 3.95 have been investigated by using SEM and EDAX techniques.     

Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Substitution of Ca by La in initial cubic double perovskite Ba₄(Ca₂Nb₂)O₁₁[VO]₁ allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} [VO]_{1 ? 0.5x} (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the predominantly hole nature of conductivity in the high-temperature region (T > 600°C) and to predominance of proton conductivity in the low-temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simultaneous mass-spectrometric determination of evolved H₂O and CO₂. The properties of the studied Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba_{4 ? x} La _x (Ca₂Nb₂)O_{11 + 0.5x} phases with similar lanthanum content.     

Van der Waals Gaps in Sm1+x Ba2−x Cu3O y and Their Effect on Superconductivity

We have used electron–positron annihilation to study superconducting cuprates Sm_1+x Ba_2–x Cu₃O _y . We have determined the average radii for oxygen ions in Sm_1+x Ba_2–x Cu₃O _y . Taking into account the ion coordinates and their radii, we have constructed a geometric model for the arrangement of copper and oxygen ions in CuO₂ layers in the [b, c] plane, responsible for the superconductivity. From these data, we have determined the length of the ionic/covalent bonds and the width of the interionic gaps. We have established the effect of the features of the atomic structure of Sm_1+x Ba_2–x Cu₃O _y on the superconducting transition temperature T _c and we have shown that T _c increases as X inceases.     

Electroconductance of single-crystal Li2 + x Fe 2 − 2x 2+ Fe x 3+ (MoO4)3 (x = 0.22)

Electrophysical properties of single-crystal Li_{2 + x} Fe _{2 ? 2x} ²⁺ Fe _x ³⁺ (MoO₄)₃ (x = 0.22) are studied at 25–400°C. It is found that the conduction is of electronic nature and the conductivity equals 5 × 10^-2 S/cm at 300°C. The activation energy for the electron transport is 0.23 eV. The conductance in molybdate Li_2.22Fe _1.56 ²⁺ Fe _0.22 ³⁺ (MoO₄)₃ is markedly anisotropic.     

Conductometric studies of thermodynamics of complexation of Li+, Na+ and K+ ions with 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6 in binary acetonitrile–nitromethane mixtures

The complexation reactions between 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6 (DTBDB18C6) and Li⁺, Na⁺ and K⁺ ions were studied conductometrically in different acetonitrile–nitromethane mixtures at various temperatures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance-mole ratio data at different temperatures. At 20 °C and in nitromethane solvent, the stability of the resulting complexes varied in the order K⁺ > Na⁺ > Li⁺. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture. The TΔS° versus ΔH° plot of thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reactions. The ab initio studies calculated at B3LYP/6-31G level of theory, indicate the binding energy of complexes decreases with increasing cation size in the gas phase. In the solution phase, DTBDB18C6 preferentially forms complexes with the larger ions rather than the smaller ions because the solvation energies of the smaller ions are large enough to overcome and reverse the trends in gas phase complexation. The findings of this study suggest that the current understanding of the factors influencing the selectivity of metal ion complexation by crown ethers may be in need of revision.