Acetonitrile-dimethylsulfoxide Mixtures Research Articles

Thermodynamics of Na+ Cl− ion – pair association in acetonitrile–dimethyl sulfoxide mixtures

Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures have been performed as a function of salt concentration and the composition of mixtures. Temperature dependence of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.

A conductivity study of preferential solvation of lithium ion in acetonitrile-dimethyl sulfoxide mixtures

The electrical mobility of LiPF6 in acetonitrile–dimethyl sulfoxide (ACN–DMSO) mixtures, a potential electrolyte in oxygen cathodes of lithium-air batteries, has been studied using a very precise conductance technique, which allowed the determination of the infinite dilution molar conductivity and association constant of the salt in the whole composition range. In the search for preferential Li+ ion solvation, we also measured the electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF6), a salt formed by a bulky cation, over the same composition range. The results show a qualitative change in the curvature of the LiPF6 molar conductivity composition dependence for ACN molar fraction (xACN)∼0.95, which was not observed for TBAPF6. The dependence of the measured Li/Li+ couple potential with solvent composition also showed a pronounced change around the same composition. We suggest that these observations can be explained by Li+ ion preferential solvation by DMSO in ACN–DMSO mixtures with very low molar fractions of DMSO.

The influence of solvation on the stability constants of Ag+-18-crown-6 complexes in acetonitrile-dimethylsulfoxide mixtures at 298.15 K

The influence of the composition of acetonitrile-dimethylsulfoxide solvents on the stability of silver(I) complexes with 18-crown-6 ether was studied potentiometrically. An increase in the concentration of dimethylsulfoxide decreased the stability of the coordination compound. It was shown on the basis of the thermodynamic characteristics of solvation of the reagents that a determining factor of complex formation equilibrium shifts was the solvation effect of the Ag+ ion. An equation was suggested for predicting the stability of silver(I) coordination compounds with crown ethers and pyridine-type ligands in binary mixtures of aprotic solvents from changes in the solvation state of the central ion.

FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile–dimethylformamide, and acetonitrile–dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na + were detected in the region of the O C N deformation and CH 3 rocking mode for amide and of the S O and C S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.

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.

Nuclear magnetic resonance studies of sodium ion complexes with several crown ethers in binary acetonitrile-dimethylsulfoxide mixtures

23Na NMR measurements were used to determine the stoichiometry and stability of Na + complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo- 15-crown-5 (B15C5), 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetonitrile-dimethylsulfoxide mixtures. With the exception of 12C4, in all other cases, the variation of the 23Na chemical shift with the crown/Na + mole ratio indicated the formation of 1:1 complexes. However, in the case of 12C4, evidence for the formation of both 1:1 and 2:1 (ligand to metal) complexes was observed. The formation constants of the resulting complexes were evaluated from the computer fitting of the mole ratio data to the equations which relate the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order 15C5 > DC18C6 > B15C5 > 18C6 > DB18C > 12C4, while in pure dimethylsulfoxide the stability order is DC18C6 > 18C6 > 15C5 > B15C5 > DB18C6 > 12C4. The observed changes in the stability order could be related to the specific interactions between some crown ethers and acetonitrile. It was found that, in all complexes studied, an increase in the percentage of dimethylsulfoxide in the acetonitrile-dimethylsulfoxide solvent mixtures would drastically decrease the stability of the resulting complexes.

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.

SPECTROPHOTOMETRIC STUDY OF THE THERMODYNAMICS OF INTERACTION OF SOME METAL IONS WITH MUREXIDE IN BINARY ACETONITRILE-DIMETHYLSULFOXIDE MIXTURES

Abstract Complexation reactions between murexide and Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ ions have been studied in different acetonitrile-dimethylsulfoxide mixtures at various temperatures by a spectrophotometric technique. Formation constants of 1:1 and 2:1 (murexide to metal ion) complexes were determined from the absorbance-mole ratio data and found to vary in the order Cu2+ > Cd2+ > Ni2+ Co2+ > Zn2+ > Pb2+. A linear relationship is observed between log β2 for different complexes and the mole fraction of acetonitrile in the solvent mixture. Enthalpy and entropy data for complexation were determined from the temperature dependence of stability constants. From the thermodynamic data obtained, the TΔS∗ - ΔH∗ plot shows a fairly good linear correlation and indicates enthalpy-entropy compensation in the reactions.

Conductance study of the thermodynamics of some transition and heavy metal cryptates in binary acetonitrile-dimethylsulfoxide mixtures

A conductance study of the interaction between Co2+, Ni2+, Cu2+, Cd2+, Zn2+ and Pb2+ ions with cryptands C211, C221 and C222 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting metal cryptates were determined from the molar conductance-mole ratio data. It was found that the stability of Co2+, Ni2+, Cu2+ and Zn2+ cryptates vary in the order C211>C221>C222, while for Cd2+ cryptates the stability order is C221>C222>C211. A linear relationship is observed between logKf of different metal cryptates and the mole fraction of acetonitrile in the solvent mixture. The enthalpy and entropy of cryptate formation reactions were determined from the temperature dependence of the formation constants. The enthalpy and entropy changes are quite sensitive to the solvent composition and the resultingTΔS0−ΔH0 plot shows a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the cryptate formation reactions.

Conductance and Viscometric Studies of Some Tetraalkylammonium and Sodium Salts in Acetonitrile-Dimethyl Sulfoxide Mixtures at 35 °C

Molar conductances and viscosities of Bu4NBPh4, NaBPh4 and R4NBr (R ethyl, propyl and butyl) at 35 °C in acetonitrile (AN), dimethylsulfoxide (DMSO) and their binary mixtures have been reported. The conductivity data has been analysed by the Shedlovsky conductance equation and viscosity data by the Jones-Dole equation. Resolution of limiting molar conductivity (Λ0) and viscosity B coefficient of electrolytes into their ionic components have been achieved by the reference salt method. Viscosity A coefficients have been compared with theoretical Aη coefficients. Derived conductance and viscosity parameters have been discussed in terms of the ion-solvent interaction.

Calorimetric study of the solvation of some ions in acetonitrile-dimethylsulfoxide mixtures

The heats of solution of LiClO 4, LiCl, NaClO 4, NaBPh 4, Co(ClO 4) 2, Ph 4AsCl and Ph 4AsClO 4 were measured in acetonitrile (AN)-dimethylsulfoxide (DMSO) mixtures over the whole range of solvent composition. The heats of transfer of single ions from DMSO to AN-DMSO mixtures were determined, based on the tetraphenylarsonium tetraphenylborate (TATB) assumption. The variation in the ionic heats of transfer with solvent composition is discussed.

Solvent Effects on the Formation of Copper(II) Chloro Complexes in Acetonitrile-Dimethyl Sulfoxide Mixtures

Abstract Complexation of copper(II) with chloride ions has been calorimetrically and spectrophotometrically studied in various acetonitrile (AN)–dimethyl sulfoxide (DMSO) mixtures at 25 °C. Complexation of copper(II) ion with DMSO as a ligand in AN has also been investigated calorimetrically. It is indicated that the solvent effect on the thermodynamic parameters of the complexation is dominated by two factors, (1) the preferential solvation of copper(II) ion with DMSO that mainly affects the enthalpies, and (2) the change in solvent–solvent interactions in the bulk that strongly affects the corresponding entropies.