The Velocity Constants of Free Ions and Ion Pairs. II

The distribution of the intercharge distance of ion pairs was derived from a solvated ion pair model. The calculation was applied to a fluorenylsodium-tetrahydrofuran system, and the equilibrium constants for the equilibria, contact ion pairs ? solvent separated ion pairs ? free ions, were calculated. Furthermore, the enthalpy and entropy changes for the equilibria were derived. Agreement with experimental data was satisfactory.     

Tetraalkylammonium Picrates in the Dichloromethane–Water System: Ion-Pair Formation and Liquid–Liquid Distribution of Free Ions and Ion Pairs

Equilibria concerning picrates of tetraalkylammonium ions (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, Bu₃MeN⁺) in a dichloromethane−water system have been investigated at 25 ^∘C. The 1:1 ion-pair formation constants (K _IP,o ^o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K _D ^o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K _IP,o ^o value varies in the cation sequence, Bu₄N⁺ ≈ Pr₄N⁺ ≈ Et₄N⁺ < Bu₃MeN⁺ < < Me₄N⁺; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs determined by density functional theory calculations. For the ion pairs of the symmetric R₄N⁺ cations, there is a linear positive relationship between log₁₀ K _D ^o and the number of methylene groups in the cation (N _{CH 2}). The ion pair of asymmetric Bu₃MeN⁺ has a higher distribution constant than that expected from the above log₁₀ K _D ^o versus N _{CH 2} relationship. These cation dependencies of log₁₀ K _D ^o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log₁₀ K _D ^o value of the free cation increases linearly with N _{CH 2}; the variation of log₁₀ K _D ^o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one, and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies of the ion-pair extractability and ion pairing in water are also discussed. An erratum to this article can be found at     

ChemInform Abstract: Steric Activity of the Central Atom Free Valence Electron Pairs in Free BrF- 6 and IF- 6 Ions.

Raman polarization and ¹⁹F NMR spectra are recorded for MeCN solutions of CsBrF₆ and CsIF₆.     

金属硫蛋白加质子常数及与Cd(II)络合常数测定

用pH计和Cd离子选择电极测定了金属硫蛋白的加质子常数及其与Cd(Ⅱ)的络合常数, 用改进的简化络合模型处理实验结果, 得到了去金属硫蛋白(apo MT)中6类不同的加质子基团的数目及其加质子常数。对Cd(Ⅱ)滴定数据的计算表明, MT中两个结构域——α和β对Cd(Ⅱ)的络合常数相差约1000倍。从热力学定量描述了MT中两个结构域结合金属离子选择优先顺序。     

Reversed-Phase HPLC. Determination of Ionic Surfactants As UV-Absorbing Ion Pairs

Abstract

Ionic and amphoteric surfactants were separated on reversed-phase columns. Ultraviolet photometry and differential refractometry were employed so that ion pairing and nonpairing compounds could be distinguished. Analysis of ionic surfactants as ultraviolet (UV) absorbing ion pairs improved detection limits 100 fold compared to detection by differential refractometer (RI).     

金属离子酸的离解常数与金属离子存在下滴定游离酸的理论处理

金属离子酸的离解常数可推导为Ka=Kw·K_(MOH)及Ka_n=Kw·K_(M(OH)n)。在金属离子存在下滴定游离酸,可以作为混合酸进行理论处理,使用相同的滴定条件与等当点pH计算公式。在加入掩蔽剂滴定时,可以使用金属离子酸的条件稳定常数作出相似的理论处理。     

Anomalous 13C Isotropic NMR Shifts in Tetraalkylammonium Tetrahalometallate(II) Ion Pairs. I. Organic Substituent Effects

¹³C isotropic NMR shifts have been recorded for a number of tetrahalocobaltate(II) salts containing various quaternary ammonium cations in dichloromethane and nitrobenzene solution. The isotropic shifts are a consequence of ion- aggregate formation, and show great sensitivity to changes in the organic substituents about the -onium centre. The ¹³C shifts appear to be due in large measure to a predominantly Fermi contact (through-bond) mechanism, unlike the more usual shifts encountered in lanthanide-containing systems. The observed shift patterns correlate well with steric effects induced by the presence or absence of bulky substituents near the central cation nitrogen atom.     

Halocyclopropenium-Halide Halogen-Bonded Ion Pairs and Their Hydrogen-Bonded Halide Solvates

A series of salts with a diaminohalocyclopropenium cation and halide anion [C₃(NⁱPr₂)₂X]X (X=Cl ([ 1 ]Cl) or Br ([ 2 ]Br) were isolated with a variety of solvates and, in one case, as a co-crystal with hydronium chloride. In particular, the initial synthesis of [ 1 ]Cl formed a co-crystal with hydronium and with CH₂Cl₂ solvate ([ 1 ]₂[OH₃Cl₃] ⋅ CH₂Cl₂) upon isolation from acetone/CH₂Cl₂. Recrystallization of this from chloroform gave a dichloroform adduct [ 1 ]Cl ⋅ 2CHCl₃, whereas treatment with ICl formed an octahalide cluster [ 1 ]₂I₄Cl₄. The bromine salt [ 2 ]Br ⋅ C₂H₄Br₂ was prepared by treatment of [ 1 ]Cl with dibromoethane and was isolated as a solvate. The hydronium cation was found as part of a hydronium trichloride cluster [OH₃Cl₃]²⁻ and this, along with a partially-deuterated analogue of [OHD₂Cl₃]²⁻ and [OD₃Cl₃]²⁻, was studied computationally and by mid- and far-infrared spectroscopy. Significant halogen bonds were found between 1 ⁺ or 2 ⁺ and chloride or bromide, respectively. On the other hand, the distance to the octahalide [I₄Cl₄]²⁻ is too long for a halogen bond. Hydrogen bonding from the halides to the halomethane solvates is also significantly stronger than to the cation isopropyl groups. The geometries formed at the halide ions with respect to the halogen bond and strong hydrogen bonds are pyramidal with approximately orthogonal angles.     

Ce3+、Tb3+离子及Ce3+-Tb3+离子对在Sr4Si3O8Cl4基质中发光的研究

研究了Ce³⁺、Tb³⁺、离子及Ce³⁺-Tb³⁺离子对在Sr₄Si₃O₈Cl₄基质中的发射光谱和激发光谱。初步讨论了Ce³⁺、Tb³⁺离子之间发光敏化的机理。     

Solvatochromism of Heteroaromatic Compounds: XXI. Ion Pairs of 4-Nitropyrazolide Anion

The solvatochromism of the long-wave UV absorption band of the contact ion pairs of the 4-nitropyrazolide anion with alkali metal cations in aprotic protophilic solvents with 24 was studied and quantitatively described using the Kamlet-Taft empirical solvent parameters. Of two possible types of tight ion pairs differing in the murtual arrangement of the counterions, the solvent stabilizes the pair in which the cation is located in the plane of the anion in the vicinity of its nitrogen atoms. Among the factors affecting the quantitative characterisitcs of the solvatochromism of such ion pairs, the major factors are the polarity/polarizability of the solvent and the capability of its molecules for coordination with cations. The peripheral specific solvation of the cation in an ion pair stabilizes its Franck-Condon excited state relative to the ground electronic state. In the quantitative respect, this effect is similar to that characteristic of solvation H complexes.     

Initial Velocity Distribution of MALDI/LDI Ions Measured by Internal MALDI Source Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry

A new method for measuring the ion velocity distribution using an internal matrix-assisted laser desorption/ionization (MALDI) source Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer is described. The method provides the possibility of studying ion velocities without any influence of electric fields in the direction of the instrument axis until the ions reach the ICR cell. It also allows to simultaneously account for and to estimate not only the velocity distribution but the angular distribution as well. The method was demonstrated using several types of compounds in laser desorption/ionization (LDI) mode. Graphical Abstract

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Epoxidation of Olefins Catalyzed by Sulfate-based Supramolecular Ion Pairs

The development of inexpensive and effective catalysts for the epoxidation of olefins to epoxides, which are key commodities for the chemical industry, is a continuing challenge. In this context, we present a supramolecular solution with the development of new host-guest assemblies of sulfate ions and amidoammonium receptor cations that, for the first time, are shown to act as catalysts for olefin epoxidation by hydrogen peroxide under biphasic conditions. Analysis of the reaction mechanism shows that the reactive and oxidizing peroxymonosulfate is formed in the organic phase. Furthermore, a variety of readily available precursors may be used to form the supramolecular ion pairs (SIPs), which is enabling a large-scale synthesis of the catalysts while maintaining catalytic control and effectiveness.     

The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

1‐n‐Butyl‐2,3‐dimethylimidazolium (BMMI) ionic liquids (ILs) associated with different anions undergo H/D exchange preferentially at 2‐Me group of the imidazolium in deuterated solvents. This process is mainly related to the existence of ion pairs rather than the anion basicity. The H/D exchange occurs in solvents (CDCl₃ and MeCN for instance) in which intimate contact ion pairs are present and the anion possesses a labile H in its structure, such as hydrogen carbonate and prolinate. In D₂O, separated ion pairs are formed and the H/D exchange does not occur. A plausible catalytic cycle is that the IL behaves as a neutral base in the course of all H/D exchange processes. NMR experiments, density functional calculations, and molecular dynamics simulations corroborate these hypotheses.     

Distribution of Ion Species and Formation of Ion Pairs in Concentrated Polysulfide Solutions in Photoelectrochemical Transducers

Results of spectrophotometric measurements in concentrated polysulfide solutions used as electrolytes in regenerative photoelectrochemical transducers are presented. The equilibrium constants are determined and the distribution of ions species in the solutions is calculated. The effect of electrolyte solution on the output characteristics of a photoelectrochemical cell based on cadmium selenide and cobalt sulfide was studied.