Molar Conductance-mole Ratio Data Research Articles

Solution Complexation Reaction Studies of a Pyrazoloisoindol Derivative Ligand by Some Metal Ions in Acetonitrile Solution

The complexation reaction between some heavy metal ions such as: Ag + , Co 2+ , Hg 2+ , Zn 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Mn 2+ , Cr 3+ , Fe 3+ and Pb 2+ with 2,3-dimethyl-1,2-dihydro-8H-pyrazolo[5,1-a]isoindol-8-one, ligand in acetonitrile as nonaqueous solvents at 25 oC were investigated by spectrophotometric and conductometric methods. The formation constants (k f ) of the 1:1 (metal ion to ligand) complexes were calculated by computer fitting of the absorbance-mole ratio data, and molar conductance-mole ratio data at 25 oC using the KINFIT program, and found that complexes to vary in acetonitrile solvent in the order of Zn 2+ > Ag + > Cr 3+ > Ni 2+ > Hg 2+ > Fe 3+ > Cu 2+ > Cd 2+ > Co 2+ > Mn 2+ > Pb 2+ . DOI: http://dx.doi.org/10.17807/orbital.v10i6.1141

Conductometric studies and application of new Schiff base ligand as carbon paste electrode modifier for mercury and cadmium determination

ABSTRACTA new chemically modified carbon paste electrode by 2,2ʹ-((pyridine-2,6-diylbis(azanylylidene))bis(methanylylidene))diphenol (L) ligand has been made and used as a sensor for determination of trace mercury and cadmium ions with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Complexation studies of the ligand with Cu2+, Zn2+, Hg2+, Ni2+ and Cd2+ ions by conductometric method in acetonitrile–ethanol mixture at 25°C show that the ML complexes have formed. The formation constants of complexes were calculated from the computer fitting of the molar conductance–mole ratio data, and the stability of the resulting complexes varied in order of Cd2+ > Hg2+ > Cu2+ > Zn2+ > Ni2+. Then a simple and effective chemically modified carbon paste electrode with L was prepared, and the electrochemical properties and applications of the modified electrode were investigated. Under the optimal conditions, the detection limit was 0.0494 μg L−1 and 0.0782 μg L−1 for cadmium and mercury ions, respectively, and the linear range for both metal ions were from 1 to 100 μg L−1. The electrode shows high sensitivity, reproducibility and low cost, and was successfully applied to determination of Cd2+ and Hg2+ ions in water samples with recovery in the range of 97–101%.

A combined experimental and density functional theory study on the complexation ability of 15-crown-5 with Li+, Na+, K+, and NH4 + cations

The complexation processes among Li+, Na+, K+, and NH4 + cations with the macrocyclic ligand, 15-crown-5 (15C5) have been studied in acetonitrile–methanol binary mixtures at different temperatures using conductometric method. The stability constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at various temperatures. The values of thermodynamic parameters ( $$ \Updelta H_{\text{c}}^{^\circ } $$ and $$ \Updelta S_{\text{c}}^{^\circ } $$ ) for the formation of the complexes were obtained from temperature dependence of the stability constants of complexes using van’t Hoff plots. In addition, a theoretical study has been carried out using density functional theory to obtain the stability of the complexes and the geometrical structure of the 15C5 and its complexes with Li+, Na+, K+ and NH4 + cations in the gas phase. We compared the experimental data with those obtained by quantum chemistry calculations to investigate the effect of the solvent on complexation process.

Conductometric Studies of Thermodynamics of Complexation of Co2+, Ni2+, Cu2+, and Zn2+ Cations with Aza-18-crown-6 in Binary Acetonitrile-Methanol Mixtures

The complexation reactions between aza-18-crown-6 (A18C6) and Co2+, Ni2+, Cu2+, and Zn2+ ions were studied conductometrically in different acetonitrile-methanol 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. Selectivity of A18C6 for Co2+, Ni2+, Cu2+, and Zn2+ cations is sensitive to the solvent composition. At 20°C and in acetonitrile solvent, the stability of the resulting complexes varied in the order but the order was reversed byadding 20% methanol. 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 decreased with increasing methanol 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. In addition, binding energies of Ni2+, Cu2+, and Zn2+ complexes with A18C6 were calculated at B3LYP/6-31G level of theory.

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.

Simultaneous separation and extraction of Ag(I), Pb(II) and Pd(II) ions by solid phase method and determination of these ions by flame atomic absorption spectrometry

A simultaneous preconcentration and separation method for determination of trace amount of dissolved Ag+, Pb2+ and Pd2+ ions by modified octadecyl silica membrane disks with DBzDA18C6 was developed. The adsorbed metal complexes were eluted from disk with 10 mL of 4 M KCl and determined by flame atomic absorption spectroscopy. Several parameters such as anion effect, pH of sample solution, type of eluent, amount of ligand, sample and elution flow rate were evaluated. The effect of diverse ions on preconcentration was also investigated. A precocentration factor of 110 can easily be achieved depending on the volume of the sample. For 100 mL of the solution the linear dynamic rang were found to be 30–1000, 140–6000, 60–900 μg l−1 for Ag+, Pb2+ and Pd2+, respectively. Based on three standard deviation of the blank the detection limit was obtained as 1.8, 8.0 and 4.2 μg L−1 for Ag+, Pb2+, Pd2+, respectively. The formation constants of Ag+ and Pb2+ ions with DBzDA18C6 at 25 °C were determined from the molar conductance–mole ratio data. This method was applied for the determination of Ag+, Pb2+ and Pd2+ in environmental water, tea and soil samples.

Spectrophotometric and conductometric studies of the thermodynamics complexation of Zn 2+ , Cu 2 + , Co 2 + , Ni +2 and Cd 2+ ions with a new schiff base ligand in acetonitrile solution

The complex-formation reactions between Cu2+, Zn2+, Co2+, Ni2+ and Cd2+ ions with 2-[(E)-(2-(2-(pyridine-2-yl)-ethylthio)ethylimino)methyl]-4-bromophenol(PYTABr) has been studied by spectrophotometric and conductometric methods in acetonitrile at various temperatures. Formation constants of the 1:1 and 1:2 (metal ion to ligand) complexes were evaluated from computer fitting of the absorbance-mole ratio data, and molar conductance-mole ratio data at different temperatures, and found that complexes to vary in the order of Ni2+>Co2+>Cu2+>Zn2+>Cd2+. The enthalpy and entropy changes of the complexation reaction were determined from the temperature dependence of the formation constants. Key words: Conductometric, spectrophotometric, formation constants, schiff bases, complexation.

Thermodynamic study for dicyclohexano-24-crown-8 complexes with K+, Rb+, Cs+ and Tl+ ions in binary acetonitrile–nitromethane mixtures by conductometric method

The complexation reactions between dicyclohexano-24-crown-8 (DC24C8) and K+, Rb+, Cs+ and Tl+ ions were studied conductometrically in the 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 25 °C and in all solvent mixtures used, the stability of the resulting complexes varied in order of Tl+ > K+ > Rb+ ~ Cs+. The enthalpy and entropy changes of the complexation reactions were evaluated by the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture.

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+.

Conductance study of the thermodynamics of complexation of amantadine, rimantadine and aminocyclohexane with some macrocyclic compounds in acetonitrile solution

A conductance study concerning the interaction between cationic organic ammonium ions amantadine, rimantadine, and aminocyclohexane with 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6) and cryptand C222 in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 1:1 cornplexes at various temperatures were determined from the computer fitting of molar conductance-mole ratio data. The enthalpy and entropy of complexation reactions were evaluated from the temperature dependence of the formation constants. The influences of different parameters such as steric hindrance of organic amines and macrocycles, conformations of the free and complexed ligands, and solvent-ligand interaction on the thermodynamic data are discussed.

Conductance Study of the Thermodynamics of Complexation of K+, Rb+, Cs+ and Tl+ Ions with Dibenzo-24-crown-8 in Binary Acetonitrile–Nitromethane Mixtures

The complexation reactions between dibenzo-24-crown-8 (DB24C8) and K+, Rb+, Cs+ and Tl+ 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 25 °C and in all solvent mixtures used, the stability of the resulting complexes varied in the order Tl+ > K+ > Rb+ > Cs+. 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° vs. ΔH° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reactions.

Conductance Study of the Thermodynamics of Binding of Some Macrocyclic Polyethers with Tl + Ion in Dimethylformamide-Acetonitrile Mixtures

The complexation reactions between Tl+ ion and dibenzo-30-crown-10 (DB30C10), dibenzo-24-crown-8 (DB24C8), dibenzo-21-crown-7 (DB21C7), and aza-18-crown-6 (A18C6) were studied in different dimethylformamide-acetonitrile mixtures at various temperatures. The formation constants of the resulting 1 : 1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order A18C6 > DB30C10 > DB21C7 > DB24C8. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants.

Conductance Study of the Thermodynamics of Tl+ ion Complexes with Different 18-Membered Crown Ethers in Binary Dimethylformamide-Acetonitrile Mixtures

A conductance study of the interactionbetween Tl+ ion and 18-crown-6 (18C6),dicyclohexano-18-crown-6 (DC18C6), benzo-18-crown-6(B18C6), diaza-18-crown-6 (DA18C6),dibenzyldiaza-18-crown-6 (DBzDA18C6) andhexaaza-18-crown-6 (HA18C6) indimethylformamide-acetonitrile mixtures was carriedout at various temperatures. The formation constantsof the resulting 1 : 1 complexes were determined fromthe molar conductance-mole ratio data and found tovary in the order HA18C6 > DA18C6 > DBzDA18C6 >18C6 > DC18C6 > B18C6. The enthalpy and entropy ofthe complexation reactions were determined from thetemperature dependence of the formation constants.

Conductance Study of Binding of Some Rb+ and Cs+ Ions by Macrocyclic Polyethers in Acetonitrile Solution

A conductance study of the interaction between Rb+ and Cs+ ions and18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6),dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) inacetonitrile solution has been carried out at various temperatures. The formationconstants of the resulting 1:1 complexes were determined from the molarconductance-mole ratio data and found to vary in the orderDC18C6 > 18C6 > DB30C10 > DB18C6 ∼ DB24C8for Rb+ ion andDC18C6 > 18C6 > DB30C10 ∼ DB24C8 > DB18C6for Cs+ ion. The enthalpy and entropy of complexation were determined fromthe temperature dependence of the formation constants. The complexes with the18-crowns are both enthalpy and entropy stabilized while, in the case of largecrown ethers, the corresponding complexes are enthalpy stabilized but entropydestabilized.

Conductance Study of Complexation of Lead Ions by Several 18-Membered Crown Ethers in Acetonitrile-Dimethyl Sulfoxide Mixtures Between 25 and 55°C

A conductance study of the interaction between Pb2+ ion and 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexyl-18-crown-6 (DC18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DAI8C6), dibenzopyridino-18-crown-6 (DBPy18C6), and dibenzyldiaza-18-crown-6 (DBzDA18C6) in acetonitrile–dimethyl sulfoxide mixtures was carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance–mole ratio data and found to vary in the order DA18C6 > A18C6 > DBzDA18C6 > DC18C6 > 18C6 > B18C6 > DBPy18C6. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes are enthalpy stabilized, but entropy destabilized. A linear relationship is observed between log Kf of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TΔS0vs. ΔH0 plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy–entropy compensation in the complexation reactions.

Synthesis of 4′-Carboxy-benzo-30-crown-10 and a Thermodynamic Study of Its Complexes with Thallium and Alkali Cations in Acetonitrile Solution

A synthetic procedure has been developed for the preparation of 4‘-carboxy-benzo-30-crown-10. The formation of Na+, K+, Rb+, Cs+ and Tl+ complexes with the large crown ether was investigated conductometrically in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data. It was found that the stability of the complexes vary in the order Tl+ > K+ > Rb+ > Cs+ > Na+. The data obtained in this study support the existence of a ‘wrap around’ structure for the above complexes in solution. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the complexes were enthalpy stabilized but entropy destabilized. The resulting TΔS° vs. ΔH°plot showed a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the large crown complexation reactions.

CONDUCTANCE STUDY AND THERMODYNAMICS OF SOME SUBSTITUTED AMMONIUM SALTS WITH CROWN ETHERS IN AQUEOUS SOLUTION

A conductance study of the interaction between substituted ammonium ions with three crown ethers in aqueous solution has been carried out at different temperatures. The formation constants of the 1 : 1 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order 18C6 > 15C5 > 12C4 for the same salt and with the same crown, the formation constants vary in the order (C2H5)3NHCl > (C2H5)4NBr > (CH3)3NPhI.

Thermodynamic study of the binding of hexathia-18-crown-6-tetraone with some transition and heavy metal ions in dimethyl sulfoxide solution

A conductance study of the interaction between CO2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+ ions with hexathia-18-crown-6-tetraone in dimethyl sulfoxide solution has been carried out at various temperatures. Formation constants of the resulting 1:1 complexes were determined from the molar conductance–mole ratio data and found to vary in the order Hg2+>Pb2+>Cd2+>Cu2+>Ni2+>Co2+>Zn2+. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. All complexes formed were enthalpy stabilized but entropy destabilized.

Complex Formation of Some Anilinium Ion Derivatives with 18-Crown-6, 1,10-diaza-18-crown-6 and Cryptand C222 in Acetonitrile, Dimethylformamide and their 1 : 1 Mixture

The complexation reactions between the protonated salts of aniline, o-hydroxy aniline, o-amino aniline and 2,3-benzo aniline (α-naphthylamine) and macrocyclic ligands 18-crown-6,1,10-diaza-18-crown-6 and cryptand C222 have been studied conductometrically in acetonitrile, dimethylformamide and their 1 : 1 (mol–mol) mixture at 25 °C. Formation constants of the resulting 1 : 1 complexes were determined from the computer fitting of the molar conductance-mole ratio data. In all cases studied, the stability of the complexes decreases in the order C222 > 1,10-diaza-18-crown-6 > 18-crown-6. There is also an inverse relationship between the stabilities of the complexes and the Gutmann donor number of the solvents. It was found that, in the aromatic anilinium series used, increasing the bulkiness of the organic substituent in the ortho position results in a loss of complex stability.

Conductance study of some transition and heavy metal complexes with 1,10-diaza-18-crown-6 in binary acetonitrile-dimethylsulfoxide mixtures

A conductance study of the interaction between cobalt, nickel, copper, zinc, cadmium, and lead ions with 1,10-diaza-18-crown-6 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting 1∶1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order Zn2+<Co2+<Ni2+<Cu2+<Cd2+<Pb2+. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. A linear relationship is observed between the log Kf of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TΔS vs. ΔH plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy-entropy compensation in the complexation reactions.