Treatment of triple ion formation

It is shown that the full Fuoss-Hsia equation can be extended to fit conductivity data for electrolyte solutions in which ion pairs and triple ions exist at comparable concentrations. The treatment is a three parameter fit of °, K _a , and K _t (the limiting molar conductivity, the thermodynamic ion association constant, and the thermodynamic triple ion formation constant, respectively). Using literature conductivity data for 1:1 electrolytes in solvents of low permittivity, it is demonstrated that an excellent fit can be achieved over a wide concentration range. Limitations of the treatment are discussed.     

Indirect ultraviolet detection of alkaline earth metal ions using an imidazolium ionic liquid as an ultraviolet absorption reagent in ion chromatography

A convenient and versatile method was developed for the separation and detection of alkaline earth metal ions by ion chromatography with indirect UV detection. The chromatographic separation of Mg²⁺, Ca²⁺, and Sr²⁺ was performed on a carboxylic acid base cation exchange column using imidazolium ionic liquid/acid as the mobile phase, in which the imidazolium ionic liquid acted as an UV‐absorption reagent. The effects of imidazolium ionic liquids, detection wavelength, acids in the mobile phase, and column temperature on the retention of Mg²⁺, Ca²⁺, and Sr²⁺ were investigated. The main factors influencing the separation and detection were the background UV absorption reagent and the concentration of hydrogen ion in ion chromatography with indirect UV detection. The successful separation and detection of Mg²⁺, Ca²⁺, and Sr²⁺ within 14 min were achieved using the selected chromatographic conditions, and the detection limits (S /N = 3) were 0.06, 0.12, and 0.23 mg/L, respectively. A new separation and detection method of alkaline earth metal ions by ion chromatography with indirect UV detection was developed, and the application range of ionic liquids was expanded.     

Influence of tetraalkylammonium ions on structure of nonaqueous solvents

Summary The half-wave potentials of the redox system [Co(en)₃]³⁺/[Co(en)₃]²⁺ have been influenced by the tetraalkylamonium cation of the supporting electrolyte used. This was explained with the specific interactions (solvation) of the tetraalkylamonium ion with the nonaqueous solvent.

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Einfluß von Tetraalkylammoniumionen auf die Struktur nichtwäßriger Lösungsmittel (Kurze Mitt.)

Zusammenfassung Das Halbwellenpotential des Redoxsystems [Co(en)₃]³⁺/[Co(en)₃]²⁺ wird von Tetraalkylammonium-Ionen des Stützelektrolyten beeinflußt. Dies wird durch die spezifischen Wechselwirkungen (Solvatation) der Ionen mit dem nichtwäßrigen Lösungsmittel erklärt.

     

Use of Ionic liquids as additives in ion exchange chromatography for the analysis of cations

The behavior of acids (citric acid, nitric acid, oxalic acid, tartaric acid) as a mobile phase and imidazolium ionic liquids (the bromides, tetrafluoroborates and hexafluorophosphates of 1‐ethyl, 1‐butyl, and 1‐hexyl‐3‐methylimidazolium) as additives in ion exchange chromatography for cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) separation were studied. The results showed that nitric acid and 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate offered the most interesting features in the separation of cations, such as lower retention time and better resolution. The selected optimal conditions were achieved by adding 0.10 mM 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate in 4.0 mM HNO₃ mobile phase for the separation of four cations with the flow rate of 0.9 mL/min at room temperature (25°C). The linear regression equations of Na⁺, K⁺, Mg²⁺, Ca²⁺ were S  = 4.4763c  + 0.0209, S  = 3.8903c  – 0.0087, S  = 6.3974c  – 0.0173, and S  = 7.601c  – 0.0339 and the limits of detection of Na⁺, K⁺, Mg²⁺, Ca²⁺ were 0.296, 4.98, 0.0970, and 1.22 μg/L, respectively. In this work, four cations in samples were successfully detected.     

含[AMIM]BF4的聚甲基丙烯酸甲酯基凝胶聚合物电解质的制备与改性

用两步法合成了离子液体1-烯丙基-3-甲基咪唑四氟硼酸盐（[AMIM]BF4）,将聚甲基丙烯酸甲酯(PMMA)引入离子液体[AMIM]BF4中,制备出含离子液体[AMIM]BF4的新型凝胶聚合物电解质,采用非质子溶剂、纳米SiO2等对其进行了改性。 用FT-IR、交流阻抗（AC）、TG、SEM等测试技术对其结构和性能进行了表征。 结果表明,非质子溶剂碳酸丙烯酯、碳酸二甲酯和纳米SiO2的加入使聚合物电解质的室温离子电导率增大,达5.25×10-3 S/cm;电导率与温度的关系符合Arrhenius方程;几种凝胶聚合物电解质的热分解温度均高于300 ℃,显示出良好的热稳定性。     

The effect of cation size on ion pairing of methyl orange dye with tetraalkylammonium and benzyltrialkylammonium ions in aqueous solution

Formation constants have been measured by a solvent distribution method for the ion pairing of an arene sulfonate, methyl orange dye, with two series of quaternary ammonium ions: R₄N⁺(R=Et,n-Pr,n-Bu, andn-Pent) and C₆H₅CH₂R₃N⁺ (R=Me, Et,n-Pr,n-Bu,n-Pent, andn-Hex). Ion pairing increases dramatically as the length of the R group increases beyond butyl. Using a hard-sphere model for contact ion pairs, it is estimated that coulombic attraction contributes about –kT to the binding free energy and decreases slightly with increasing size of R₄N⁺. Other factors related to solvation effects, of which cosphere overlap predominates, contribute from –2kT to –7kT of binding energy. Plots of logK for association as a function of cation size show an inflection with decreasing slope between R=propyl and R=butyl. Possible causes for the inflection are considered.     

Infrared spectra of M+NO 3 − contact ion pairs in aprotic solvents and matrix isolated in the corresponding glasses

Studies of the vibrational spectra of matrix-isolated M⁺NO ₃ ^– ion pairs have been extended to glassy aprotic solvents. The deuterated form of the solvents DMSO, THF, and ACN have windows through the 7- nitrate ionv ₃(e) mode infrared region, so it was possible to clearly observe the splitting of the degeneracy of this mode,v ₃, produced by the contacting, but solvated, alkali metal cation. Primary attention has been directed to the extent to which this splitting is reduced relative to the argon matrix values. This reduction, which reflects electron-density transfer from the solvating molecules to the ion pairs, is comparable to that observed for H₂O and NH₃ matrices as the splitting is reduced to 20–35% of the argon-matrix values. The extent of reduction ofv ₃ for the different solvents has been related to Gutmann's donicity number scale with the correlation holding well for solvent molecules of comparable size, DMSO, THF and DMF, but breaking down for the smaller linear ACN, apparently because of more molecules in the cation solvation sphere. The matrix data have also been used, through comparison with spectra for saturated liquid solutions of Li⁺NO ₃ ^– , to show that the contact ion pair is the dominant species in liquid THF and ACN, whereas the ions are largely solvent separated in DMSO.     

Vibrational Spectra and Ion-Pair Properties of Lithium Hexafluorophosphate in Ethylene Carbonate Based Mixed-Solvent Systems for Lithium Batteries

The vibrational spectra of LiPF₆ 1M solutions formed in aprotic mixed solventsobtained by mixing ethylene carbonate with dimethyl carbonate and diethylcarbonate are discussed. The Raman and infrared spectra of lithium hexafluorophosphate(LiPF₆) and the quantum chemical computations of the vibrationalwavenumbers and intensities are reported. Due to the nature of the solutions,attenuated total internal reflectance spectroscopy was used to obtain the infraredspectra. The infrared active vibrational fundamentals of PF₆ ^– provided evidencefor the anion—solvent interaction as well as ion-pair formation. Similarly, theinfrared active modes of the solvent showed significant changes due to thecation—solvent interaction. The computations of the most energetically favorablegeometry in the formation of the Li⁺ PF₆ ion pair are also presented. Conductivitymeasurements carried out for the 1M solutions scanning a wide temperatureinterval (–30 to + 60 °C) confirm the viability of these electrolytes forpractical applications.     

On the detection by EXAFS spectroscopy of multimeric species and of complex anions in diethylether and diethylcarbonate

EXAFS spectroscopy has been shown to be a reliable tool for detecting the formation in solutions of molecular associations (LiBr)_n where n is solvent dependent. The signal Br^*...Br observed at 3.8₇ Å confirms the formation of tetrameric species (n=4) in diethylether (Et₂O) but only of dimers (n=2) in diethylcarbonate. Another signal observed at 2.4₅ Å has·been attributed to the pair Br^*...Li. The study of Li₂MBr₄–Et₂O solutions (M=Co, Cu, Zn) also affords new evidence for the formation of complex anions MBr ₄ ^2– but the spectra obtained at the bromine or metalK-edges for LiZnBr₃–Et₂O solutions seems to indicate the formation of more complex aggregates (LiMBr₃)_q. While the signal of the shell Br^*...Br is found quite intense for the reference CBr₄–Et₂O system, it does not appear for the MBr ₄ ^2– complex except for CuBr ₄ ^2– where the Jahn-Teller effect might rigidify a distorted tetrahedral structure.Presented, in part, at the VIIth International Conference on Non-Aqueous Solutions, Regensburg, West Germany, Ausgust 1980.     

FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO ₄ ^– ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm^–1 is used for the calculation of cation solvation numbers for Li⁺(4), Na⁺(4), Mg²⁺(6), Ca²⁺(6), and Ba²⁺(6). No solvation is assumed for the contact ion pairs of LiClO₄, LiBr, NaClO₄, Mg(ClO₄)₂, Ca(ClO₄)₂, and Ba(ClO₄)₂. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.     

Ion-solvent molecule interaction in nonaqueous solutions: Spin-lattice relaxation time of7Li

The spin-lattice relaxation time (T ₁) of⁷Li⁺ was measured in solutions of LiCl and LiClO₄ in protic (MeOH, EtOH,n-PrOH,i-PrOH,n-BuOH, sec-BuOH, formamide, N-methylformamide) and aprotic (MeCN, acetone, methyl ethyl ketone, propylene carbonate, dimethyl sulfoxide, dimethylformamide, hexamethylphosphotriamide) solvents and in mixtures of H₂O-formamide, H₂O–N-methylformamide, H₂O–N,N-dimethylformamide, H₂O-DMSO, H₂O-hexamethylphosphotriamide, and formamide-N,N-dimethylformamide at 25°C. The values of (1/T ₁)₀ obtained by extrapolation are discussed in terms of current theories of the magnetic relaxation of ionic nuclei. Linear correlations were found between (1/T ₁)₀ and Gutmann's donor numbers and Kosower's Z-values. These correlations indicate that relaxation of⁷Li⁺ is dominated by donor-acceptor interaction of the cation with solvent molecules. Concentration dependences of 1/T ₁ for LiCl and LiClO₄ differ from one another in a given solvent, a fact which is accounted for by a specific cation-anion short-range potential. The quantity 1/T ₁ of⁷Li⁺ atC=1 mole per 55.5 moles of mixed solvent as a function of solvent composition show characteristic features, which are discussed in terms of the relaxation mechanism proposed.     

Conductances of some electrolytes in 2-methylpyridine-N-oxide at 55°C

Conductance measurements for fifteen uni-univalent salts in 2-methylpyridine-N-oxide (2-MPO) were made over the concentration range of 2–120×10^–4 mol-dm^–3 at 55°C. All conductance data were evaluated by the Lee-Wheaton equation. The results indicate that all of the salts studied are slightly associated in 2-MPO, which is, nevertheless, a reasonably good ionizing solvent compared to other solvents having a similar value for the dielectric constant. The tetraalkylammonium halides are weaker electrolytes than the tetraphenylborate salts in 2-MPO. Ionic limiting molar conductances were obtained by using as a reference electrolyte tris(iso-pentyl)butylammonium tetraphenylborate. Anions appear to be poorly solvated in this solvent but certain cations, particularly Na⁺ and K⁺, show evidence of specific ion-solvent interaction.This study was presented, in part, at the 6th Central Regional Meeting of the American Chemical Society, Detroit, Michigan, April 1974.     

A glass formation study of aqueous tetraalkylammonium nitrate solutions

The glass-forming composition regions of aqueous tetraalkylammonium nitrate solutions (alkyl = ethyl and n-propyl) were determined by a simple DTA method with a cooling rate of about 600 K-min^–1. The glass transition temperatures T_g of these solutions vary in a different manner from those for simple inorganic salt solutions such as aqueous LiCl, MgCl₂,and AlCl₃ solutions. Liquid-liquid immiscibilities are observed in these solutions at low temperatures.     

Viscosities of solutions of electrolytes and non-electrolytes in ethylene carbonate at 40°C

The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, tetrabutylammonium tetrabutylborate, water, and 3,3-diethylpentane have been measured in the high-dielectric constant solvent, ethylene carbonate (EC) at 40°C. Crude values of the apparent molar volumes of these solutes have also been obtained. Relative viscosities were fitted to the extended Jones-Dole equation, _r=17#x002B;A c ^1/2+B C+D c ².The pattern of the B coefficients is strikingly similar to that previously observed in the high dielectric constant, linear-chain hydrogen-bonded solvent, N-methylacetamide (NMA). Ionic values for _v and B have been obtained using a variety of splitting techniques. Alkali metal ions have large B coefficients indicating strong cation solvation with the normal order Li>Na>K>Cs. Small anions have positive but much smaller B values than in NMA. The observed order does suggest, however, a small degree of anion solvation. Large organic ions do not display the sharp crossing of the Einstein law,D =2.5_v, uniquely characteristic in H₂O of hydrophobic interaction. The two non-electrolytes have negative B coefficients showing that the Einstein law is not valid at the molecular level and that hydrocarbons are not good models for their isoelectronic tetraalkylammonium ion counterparts. An empirical modification of the Einstein law to account for the finite size of the solvent molecules is discussed. As in NMA the D coefficients are roughly linear in the square of B suggesting that they arise from hydrodynamic origins.     

Conductance behavior of 1∶1 electrolytes in N,N-dimethylmethanesulfonamide

The conductances of eleven 1:1 salts have been measured at 50°C in N,N-dimethylmethanesulfonamide (DMMSA) for electrolyte concentrations of 1.2–55.0×10^–4 mol-dm^–3. The conductance data were analyzed using the equation of Lee and Wheaton. Calculations for different values of the distance parameter R indicate that all salts studied are only slightly associated in DMMSA. Association was somewhat greater for the trimethylphenylammonium halides than for the tetraalkylammonium salts. Ionic limiting molar conductances were estimated using the tris (isopentyl) butylammonium tetraphenylborate approximation. The markedly smaller value for _o (Na⁺) compared to the values for _o (Br^–) and _o (I^–) indicates that the sodium ion is probably more extensively solvated than the halide ion. In general, it appears that DMMSA (dielectric constant=80.31 at 50°C) is similar in its solvent properties to dipolar aprotic heterocyclic solvents such as 2-cyanopyridine and 3-methyl-2-oxazolidone which have similar dielectric constants.     

Physico-chemical transformations in swift heavy ion modified poly(ethyleneterephthalate)

Thin films of poly(ethyleneterephthalate) (PET) were exposed to different radiation dose brought about by 80 MeV carbon and 98 MeV silicon ion beam. The UV-vis absorption studies reveal that there is decrease in optical band gap energy to the extent of ∼29.3 and 42.1%. The X-ray diffraction analyses have shown that crystallite size decreased by ∼18.6 and 52.6%, indicating amorphization of PET. The colour of PET films change from colourless to light yellowish followed by light brown as radiation dose is increased. The colour formation has been ascribed to an increase in conjugation in the carbon chain. In the case of PET irradiated with carbon ion, the electrical conductivity increased with frequency beyond a threshold value of 1 kHz. The increase in conductivity of PET films on irradiation is due to formation of defects and carbon clusters as a result of polymer chain scission. The thermal study further confirmed the increase in amorphous nature with increase in radiation dose. The results indicate that radiation dose brings about significant physicochemical transformations in PET.     

Ion-selective electrode measurements for the determination of formation constants of alkali and alkaline earth metals with low-molecular-weight ligands

Formation constants of acetate, hydrogencarbonate, malonate, citrate and 1,2,3-propanetricarboxylate complexes with Na⁺, K⁺ and Ca²⁺ were determined potentiometrically using sodium, potassium and calcium selective electrodes, at 25 °C and at different ionic strengths, in the range 0 < I ≤ 1 M. Formation constants obtained by ion-selective electrode (ISE) measurements were compared with those obtained by different techniques. It has been found that the use of ISEs gives reliable results in the study of weak complexes, also under non-constant ionic strength conditions.     

Magnetic relaxation dispersion of lithium ion in solutions of DNA

The magnetic field dependence of the nuclear spin-lattice relaxation rate constant defines the magnetic relaxation dispersion (MRD) and provides a direct characterization of the molecular dynamics that cause fluctuations in the magnetic couplings in the system and may also indicate the dimensional constraints on the motion. The counterion cloud surrounding a linear polyelectrolyte ion, such as DNA in solution, provides an interesting opportunity for ion confinement that helps in understanding the thermodynamics and the dynamics of the interactions between the polyion and other solutes. The MRD profiles of lithium ion and tetramethylammonium ion were recorded in dilute aqueous solutions of native calf thymus DNA, which provides a long, charged rod that reorients slowly. The 7Li ion relaxes through the nuclear electric quadrupole coupling and the proton-lithium dipole-dipole coupling; the protons of the tetramethylammonium ion relax by dipole-dipole coupling. MRD profiles of the 7Li+ ion are dominated by transient interactions with the DNA that yield a linear dependence of the spin-lattice relaxation rate constant on the logarithm of the Larmor frequency. This magnetic field dependence is consistent with diffusive ion motions that modulate two spatial coordinates that characterize the relaxation couplings in the vicinity of the polyion. Motions around the rod and fluctuations in the ion distance from the rod are consistent with these constraints for lithium. The magnetic field dependence of the tetramethylammonium ion proton relaxation rate constant is weak, but also approximately a linear function of the logarithm of the Larmor frequency, which implies that the field dependence is caused in part by local order in the DNA solution.     

Solubility of methane in aqueous solutions of triethylenediamine

The solubilities of methane were measured in water and aqueous solutions of triethylenediamine (TED), triethylenediamine hydrochloride (TED·HCl), and HCl at several concentrations up to 1M at 5° intervals from 5 to 25°C. Methane solubilities in solutions of TED·HCl and HCl are lower than those in water and decrease with increasing cosolute concentration. In contrast, the solubilities in TED solutions are greater than those in water and increase with increasing TED concentration. The order of methane solubilities at 25°C in water and in 0.5M aqueous solutions is TED>H₂O>HCl>TED·HCl with Ostwald coefficients of 3.57×10^–2, 3.44×10^–2, 3.26×10^–2, and 3.19×10^–2, respectively, and with an experimental precision of about ±0.2×10^–3. Thermodynamic functions for the transfer of methane from water to 0.25, 0.50, and 0.75M aqueous solutions have been calculated on the molar concentration scale. The free energies of transfer are compared with previous results for methane in aqueous solutions of tetraalkylammonium halides.