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.     

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.     

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.     

Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Rb+ ion with 18-crown-6 in binary dimethylsulfoxide–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Rb⁺ ion with 18-crown-6 (18C6) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 18C6 was fast on the NMR time scale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The ?H° versus T?S° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.     

A convenient synthesis of new thiaazacrown ethers and study of their complexation reactions with some transition metal cations in binary acetonitrile–chloroform mixture using the conductometric method

Three novel thiaazacrown ethers 1, 2 and 3 were synthesized in a simple way and in high yield. The complex formation between Ag⁺, Cu²⁺, Zn²⁺, Pb²⁺, Hg²⁺ and Cd²⁺ metal cations with thiaazacrown ethers 1, 2 and 3 have been studied in acetonitrile:chloroform (1:1) binary solvent system using conductometric technique. The conductance data show that the stochiometry of the complexes with Ag⁺, Cu²⁺ and Zn²⁺ cations is 1:1 (L:M), but in the case of Pb²⁺ and Hg²⁺ cations, a 1:2 (L:M) complex is formed in solutions. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data at 25 °C. It was found that the stability constants of 1-Ag²⁺, 2-Ag⁺ and 3-Ag⁺ complexes are higher than those of their corresponding Zn²⁺ and Cu²⁺ complexes and found to vary in order 3 > 1 > 2 for Ag⁺.     

Complexation thermodynamics of imine-type bis(benzocrown ether)s. Part I. Sandwich complexation of K+, Rb+, Cs+ and Tl+ with polymethylene andm-Phenylene bridged carbonylhydrazones of 4′-formylbenzo-15-crown-5

The complexation thermodynamics of polymethylene andm-phenylene bridged carbonylhydrazones of 4-formylbenzo-15-crown-5 with K⁺, Rb⁺, Cs⁺ and Tl⁺ was investigated by spectrophotometric titrations in methanol at 283–313 K. The carbonylhydrazone sequences in the bridge of the bis(benzocrown ether)s are optical sensors for the sandwich complexation of metal ions. Within the homologous series of polymethylene bridged carbonylhydrazones a stability peak was found for the sandwich complexes of the propylene bridged compound with K⁺, Rb⁺ and Tl⁺. The potassium complex of this ligand shows the highest stability constant compared to all other known bis(benzo-15-crown-5) complexes with K⁺ in methanol.In terms of thermodynamics the formation of intramolecular sandwich complexes is driven by a gain of enthalpy. The unusual high gains of enthalpy and losses of entropy on formation of the most stable sandwich complexes allow us to propose an additional stabilization of the sandwich arrangement by intramolecular hydrogen bridge bonds. The H ^o-TS ^o diagram gave an excellent straight line allowing discussion of the enthalpy-entropy compensation effect at these complexation reactions.     

Study on ion–solvent interactions of alkali metal salts in pure methanol and its binary mixtures with ethane-1,2-diol by a conductometric technique

Electrolytic conductivities of some sodium salts (NaI, NaSCN, CH₃COONa) have been studied in 0, 25, 50 and 75 mass% ethane-1,2-diol + methyl alcohol mixtures at 293.15, 298.15 and 303.15 K. The limiting molar conductivity (Λ°), the association constant (K_A) and the distance of closest approach of ion (R) have been evaluated using the Fuoss conductance equation (1978). The association constant (K_A) decreases with temperature while it tends to decrease in the order: 0 mass% > 25 mass% > 50 mass% > 75 mass% ethane-1,2-diol + methyl alcohol mixtures. Thermodynamic parameters ΔH°, ΔG° and ΔS° along with the Walden products (Λ°η) are obtained and discussed. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Study of complex formation between La+3, Ce+3 and Y3+ cations with some 18-membered crown ethers in methanol–water and methanol–acetonitrile binary mixtures

The complexation reactions between some rare earth metal cations (Ln; Y³⁺, La³⁺ and Ce³⁺) with 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), benzo-18-crown-6 (B18C6) and decyl-18-crown-6 (Dec18C6), have been studied in methanol–acetonitrile (MeOH–AN) and methanol–water (MeOH–H₂O) binary mixtures using a competitive spectrophotometric method. 2-(2-thiazolylazo)-4-methyl phenol (TAC or L) was used as colorimetric complexant. It was found that the selectivity order of TAC for Ln cations is highly changed with changing the composition of the mixed solvents. Moreover, as the concentration of acetonitrile increases in MeOH–AN binary mixture, the stability of Ln–TAC complexes increases and passes through a maximum at a certain mole fraction of acetonitrile. In addition, the stability of Ln–crown ether complexes increases with increasing the concentration of methanol in MeOH–H₂O and acetonitrile in MeOH–AN binary solutions. A non linear behaviour was observed for variation of stability constants of all complexes versus the composition of the mixed solvents. The results show that 18C6 generally forms more stable complexes with La³⁺ and Ce³⁺ cations than DC18C6 in methanol and MeOH–H₂O binary mixtures, while this sequence is reversed in the methanol-acetonitrile binary mixtures which are rich with respect to acetonitrile.     

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.     

Thermodynamic characteristics of complex formation by Ni2+ ions and glycylglycine in aqueous solutions of KNO3 at 288–308 K

Heat effects of the interaction between glycylglycine and nickel (II) nitrate solutions are measured by direct calorimetry at different pH values and metal: ligand ratios in the temperature range of 288.15 to 308.15 K. KNO₃ is used as the background electrolyte. The heat effects of diluting the nickel nitrate solution in solutions of the background electrolyte are determined in order to make the appropriate corrections. The standard thermodynamic characteristics of complex formation by peptides and nickel (II) ions in aqueous solution are calculated. Standard enthalpies of the formation of complex particles NiPep⁺, NiPep₂, and NiPep ₃ ^? are determined for the first time.     

Surface tension of binary and two ternary mixtures containing water–acetonitrile–methanol/ethanol at 298.15 K: experimental data,correlation and prediction by various models

Surface tension of two ternary mixtures of water/acetonitrile/methanol and water/acetonitrile/ethanol, and their constituent binaries, were measured over the whole range of composition at 298.15 K and ambient pressure. The experimental data were used to calculate in the surface tension deviations (Δσ). The negative values of Δσ for the binary and ternary systems indicate the strong hydrogen bonding between unlike molecules of mixtures (particularly in the high concentration of water). Surface tension data of the binary systems were correlated with Fu et al., Wang–Chen, Redlich–Kister and Myers–Scott models. The mean standard deviation obtained from the comparison of experimental and calculated surface tension values for binary systems with four models is less than 0.42. Finally, the concentration dependence of the surface tension deviation of the ternary mixtures at 298.15 K was correlated using Pando et al. and Ku et al. models, with satisfactory results.     

Conductometric study of complexation reaction of 4′-nitrobenzo-15-crown-5 with Mn+2, Co+2, Y+3, and ZrO+2 cations in acetonitrile,methanol and their binary solvent solutions

The complexation reactions of Mn²⁺, Co²⁺, Y³⁺, and ZrO²⁺ cations with the macrocyclic ligand, 4′-nitrobenz-15-crown-5 (4′-NB15C5), in acetonitrile (AN), methanol and AN-MeOH binary mixtures have been studied at various temperatures using the conductometric method. The conductance data stand for the Me : L stoichiometric ratio 1 : 1. Values of the formation constants of the complexes were accumulated by plotting molar conductivity curves using the computer program, GENPLOT. The order of stability of the metal-ion complexes in pure AN at 15°C was found to be: (4′-NB15C5 · ZrO)²⁺ > (4′-NB15C5 · Mn)²⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · Y)³⁺. In the case of AN-MeOH binary solvent solutions with 50 and 75 mole percent of AN at the same temperature, the sequence of stability of the complexes was the following: (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · ZrO)²⁺ ≈ (4′-NB15C5 · Co)²⁺ 〉 (4′-NB15C5 · Y)³⁺, and (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · Y)³⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · ZrO)²⁺, respectively. The complexes formed are entropy stabilized in all cases.     

A Proton NMR Study of the Stoichiometry and Stability of 18-Crown-6 Complexes with K+, Rb+ and Tl+ Ions in Binary Dimethyl Sulfoxide-Nitrobenzene Mixtures

Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K⁺, Rb⁺ and Tl⁺ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average ¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb⁺ ion forms the most stable complex with 18-crown-6 in the series.     

Thermodynamic properties of binary mixtures containing n-alkylamines: I. Isothermal vapour–liquid equilibrium and excess molar enthalpy of n-alkylamine+toluene mixtures. Measurement and analysis in terms of group contributions

Molar excess enthalpies, H^E, at 303.15 K and atmospheric pressure, of n-propyl-, n-butyl-, n-pentyl-, n-octyl- or n-decylamine+toluene, as well as the isothermal vapour–liquid equilibria, VLE, of n-butylamine+toluene and of n-butylamine+benzene at 298.15 K have been determined. These experimental results, along with the data available in the literature on molar excess Gibbs energies, G^E, activity coefficients at infinite dilution, γ_i^∞, and molar excess enthalpies, H^E, for n-alkylamine+toluene mixtures are examined on the basis of the DISQUAC group contribution model. The modified UNIFAC is also used to describe the mixtures.     

A comparative study of interplay effects between the cation-π and intramolecular hydrogen bond interactions in the various complexes of methyl salicylate with Mn+, Fe2+, Co+, Ni2+, Cu+, and Zn2+ cations

Structural Chemistry - The interplay among two important noncovalent interactions involving aromatic ring is studied by means of density functional theory (DFT) calculations on complexes of methyl...     

<Superscript>133</Superscript>Cs NMR Study of Cs<Superscript>+</Superscript> Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by ¹³³Cs NMR spectroscopy. The ¹³³Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs⁺ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.     

Novel method for determination of uranium isotopes in environmental samples by liquid–liquid extraction with triisooctylamine in sulfuric and hydrochloric acid media

Novel and robust method for determination of uranium isotopes in various environmental materials is presented. The method is based on total decomposition of the solid materials by the use of closed vessels microwave acid digestion systems and pre concentration of uranium from the liquid samples. The separation of uranium from interfering radionuclides and stable matrix elements is attained by liquid–liquid extraction with triisooctylamine/xylene in sulfuric and consecutively in hydrochloric acid media. Purified uranium is electrodeposited on a stainless steel disks and then measured by alpha spectrometry. The critical steps in the method were examined. The analytical method has been successfully applied to the determination of uranium isotopes in mineral and tap waters, as well as in soils from Northwestern Bulgaria. The analytical quality was checked by analyzing reference materials with different matrices.     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

DFT-B3LYP and SMD study on the interactions between aza-, diaza-, and triaza-12-crown-4 (A n -12-crown-4, n = 1, 2, 3) with Na+ in the gas phase and acetonitrile solution

B3LYP/6-311G level of theory is used to study the interactions between aza-, diaza-, and triaza- 12-crown-4 ligands as host molecules and Na⁺ ion as a guest species. Minimum energy structures, complexes binding energies, basis set superposition errors, and various thermodynamic parameters of free ligands, ion, and complexes have been calculated based on the proposed level of theory. A simple thermodynamic cycle with and without different acetonitrile cluster sizes inside the cavity of Na⁺, has been used to calculate the stability constants of aza-12-crown-4 complex. All solvation free energy estimations have been done with using SMD model. Results show that with introducing more acetonitrile molecules in the cavity of guest species, the absolute deviation is reduced. In addition, a good linear correlation between experimental complex formation constants and binding energies of complexes has been obtained. Calculated results, which are in agreement with the experimental data, predict that the interaction energy of triaza- is more than diaza-12-crown-4, which in turn is greater than aza-12-crown-4 with Na⁺ ion.