Contacted Ion Pairs in Aqueous CuCl2 by the Combination of Ratio Spectra, Difference Spectra, Second Order Difference Spectra in the UV-Visible Spectra

The microstructure of aqueous CuCl2 has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin fihn of CuCl2/H2O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at -230 and -380 nm are obviously observed. The bands are assigned as the contacted ion pairs [CuCl3（H2O）n]- or [CuCl4（H2O）n]2-, which demonstrates that ion pairs exist in the CuCl2/H2O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of [CuCl3（H2O）n]- or [CuCl4（H2O）n]2- in aqueous CuCl2, but also suggests that the spec- troscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.

Ion Pairing Kinetics Does not Necessarily Follow the Eigen-Tamm Mechanism

The most recognized and employed model of the solvation equilibration in the ionic solutions was proposed by Eigen and Tamm, in which there are four major states for an ion pair in the solution： the completely solvated state, 2SIP （double solvent separate ion pair）, SIP （single solvent separate ion pair）, and CIP （contact ion pair）. Eigen and Tamm suggested that the transition from SIP to CIP is always the slowest step during the whole pairing process, due to a high free energy barrier between these two states. We carried out a series of potential of mean force calculations to study the pairing free energy profiles of two sets of model mono- atomic 1：1 ion pairs 2.0：x and x：2.0. For 2.0：x pairs the free energy barrier between the SIP and CIP states is largely reduced due to the salvation shell water structure. For these pairs the SIP to CIP transition is thus not the slowest step in the ion pair formation course. This is a deviation from the Eigen-Tamm model.

Sympathetic Cooling of ^(40)Ca^(+_27)Al^+ Ion Pair Crystal in a Linear Paul Trap

The 27Al＋ ion optical clock is one of the most attractive optical clocks due to its own advantages such as low black-body radiation shift at room temperature and insensitivity to the magnetic drift. However, it cannot be laser-cooled directly in the absence of 167nm laser to date. This problem can be solved by sympathetic cooling. In this work, a linear Paul trap is used to trap both 40Ca＋ and 27A1＋ ions simultaneously, and a single Dopplercooled 40Ca＋ ion is employed to sympathetically cool a single 27A1＋ ion. Thus a ＇bright-dark＇ two-ion crystal has been successfully synthesized. The temperature of the crystal has been estimated to be about 7mK by measuring the ratio of carrier and sideband spectral intensities. Finally, the dark ion is proved to be an 27Al＋ ion by precise measuring of the ion crystal＇s secular motion frequency, which means that it is a great step for our 2Z Al＋ quantum logic clock.

Thermodynamics of Ion Pair of Magnesium Sulfate in Mixed Solvent

Introduction Magnesium sulfate is an archetypal 2-2 salt that plays a central role in defining the characteristics of higher valent electrolyte solutions and its solution has been widely used to test various theories of strong electrolyte behavior and to develop models of ion association in solution. Up to now, the ion pairs of magnesium sulfate in an aqueous solution have been widely investigated by using different experimental techniques, such as conductometry , cryoscopy potentiometry solubility and Raman spectrometry. However, to our knowledge, no measurement of the standard association constant of the ion pairs, [ MgSO4 ]^0 in a glucosewater mixed solvent is available.

The Standard Association Constant of Ion Pair [GaCl]^(2+)in the System of HCl+GaCl_3+H_2O

The standard association constants of ionic pair [GaCl]2+, Kas, were determined by emf(electromotive force) method at 278.15 to 318.15 K. The thermodynamic quantities for the ionic association process were calculated and it was pointed that the association entropy is driving force to form the ionic pair.

Ab Initio and DFT Study of Magnesium Sulfate Contact Ion Pairs

The stuctures of contact ion pairs of magnesium sulfate were studied. The geometries of contact ion pairs of MgSO 4(H 2O) n (n =1-6) were optimized by using Hartree Fock (HF/6 31+G *, HF/6 311+G ** ) and density functional theory (DFT) (B3LYP/6 31+G *, B3LYP/6 311+G ** ) methods. The stable structures of monodentate, bidentate and tridentate contact ion pairs were obtained. The bidentate structure of contact ion pairs are the most stable compaired with the monodentate and tridentate ones for the same composition. The hydration enthalpies of contact ion pairs of MgSO 4 (H 2O) n (n =1-4) increase with their hydration numbers.

EPR STUDY OF THE FORMATION OF[Li^+O^-]ION PAIR ON Li-DOPED ZnO

In this letter the study of Li-doped zinc oxide by electron paramagnetic resonance method is described.A signal observed at g_=2.013,g_=1.955 on the degassed sample at 923K was designated to F_s^+ centers(surface oxygen ion vacancies with a single trapped electron).When the sample was quenched from 1003K into liquid oxygen at 77K under 24 KPa O_2,[Li^+O^-] ion pairs valued at g_=2.026 and g=2.003 with superhyperfine constant a=2.0G,which resulted from ~7Li nucleus,formed at Li^+-substitutional site in ZnO lattice.A probable mechanism of [Li^+O^-]ion pair formation was proposed.

Stable Radical Ion Pairs Induced by Single Electron Transfer:Frustrated Versus Nonfrustrated

Single electron transition reactions between amines(Lewis base)and B(C_(6)F_(5))_(3)(Lewis acid)in cooperation with benzoquinones gave rise to a frustrated radical pair 3 and a nonfrustrated radical pair 4.Both of them were isolated as stable crystals and studied by single-crystal X-ray diffraction,superconducting quantum interference device measurements,electron paramagnetic resonance,nuclear magnetic resonance,and UV–vis spectroscopy.Antiferromagnetic exchange coupling was observed among both 3 and 4.Radical anion and cation are basically separated in 3,while 4 featured a relatively strong anion-cationπ–πstacking interaction.This work demonstrated that the Lewis acid coupled electron transfer is an efficient way to prepare stable radical ion pairs.

Novel Properties of Supramolecular Complexes Formed by Pairing Cationic Porphyrin and Anionic Metal-Oxo Cluster

MTBPyP (meso-tetrakis(4-N-benzylpyridyl)porphyrin, M=H-2, Zn) bearing positive charge has been shown to associate with SiW12O404- in water solution. The spectral evolution and Job's plots analyses reveal that the relatively stable aggregates contain equal numbers of MTBPyP4(+) and SiW12O404-.

Enhancing the process of CO_(2) reduction reaction by using CTAB to construct contact ion pair in Li-CO_(2) battery

Aprotic Li-CO_(2)batteries have attracted growing interest due to their high theoretical energy density and its ability to use green house gas CO_(2)for energy storage.However,the poor ability of activating CO_(2)in organic electrolyte often leads to the premature termination of CO_(2)reduction reaction(CO_(2)RR)directly.Here in this work,cetyl trimethyl ammonium bromide(CTAB)was introduced into a dimethyl sulfoxide(DMSO)based Li-CO_(2)battery for the first time to enhance the CO_(2)RR.Significantly improved electrochemical performances,including reduced discharge over-potential and increased discharge capacity,can be achieved with the addition of CTAB.Ab initio molecular dynamics(AIMD)simulations show that quaternary ammonium group CTA^(+) can accelerate CO_(2)reduction process by forming more stable contact ion pair(CIP)with CO_(2)^(–),reducing the energy barrier for CO_(2)RR,thus improving the CO_(2)reduction process.In addition,adding CTA^(+) is also favorable for the solution-phase growth of discharge products because of the improved migration ability of stable CTA^(+)-CO_(2)^(–) CIP in the electrolyte,which is beneficial for improving the utilization ratio of cathode.This work could facilitate the development of CO_(2)RR by providing a novel understanding of CO_(2)RR mechanism in organic system.

Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution

Ion pair speciation of ionic liquids(ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR(FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic(MD) simulation and nuclear magnetic resonance hydrogen spectroscopy(~1H NMR) to investigate ion pairs of aprotic ILs [Bmim][NO_3], [BuPy][NO_3], [Pyr_(14)][NO_3], [PP_(14)][NO_3] and [Bu-choline][NO_3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory(DFT) calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction(say 0.80 for [BuPy][NO3]). When water content was increased to a critical mole fraction of water(say 0.83 for [BuPy][NO3]), the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions(fully hydrated cations or anions). The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions(fully hydrated ion) were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and ~1H NMR results support the conclusion drawn from FIR spectra investigations.

Ion-pairing HPLC methods to determine EDTA and DTPA in small molecule and biological pharmaceutical formulations

Ion-pairing high-performance liquid chromatography-ultraviolet （HPLC-UV） methods were developed to determine two commonly used chelating agents, ethylenediaminetetraacetic acid （EDTA） in Abilify （a small molecule drug with aripiprazole as the active pharmaceutical ingredient） oral solution and die- thylenetriaminepentaacetic acid （DTPA） in Yervoy （a monoclonal antibody drug with ipilimumab as the active pharmaceutical ingredient） intravenous formulation. Since the analytes, EDTA and DTPA, do not contain chromophores, transition metal ions （Cu2＋, Fe3＋） which generate highly stable metallocom- plexes with the chelating agents were added into the sample preparation to enhance UV detection. The use of metallocomplexes with ion-pairing chromatography provides the ability to achieve the desired sensitivity and selectivity in the development of the method. Specifically, the sample preparation in- volving metallocomplex formation allowed sensitive UV detection. Copper was utilized for the de- termination of EDTA and iron was utilized for the determination of DTPA. In the case of EDTA, a gradient mobile phase separated the components of the formulation from the analyte. In the method for DTPA, the active drug substance, ipilimumab, was eluted in the void. In addition, the optimization of the concentration of the ion-pairing reagent was discussed as a means of enhancing the retention of the aminopolycarboxylic acids （APCAs） including EDTA and DTPA and the specificity of the method. The analytical method development was designed based on the chromatographic properties of the analytes, the nature of the sample matrix and the intended purpose of the method. Validation data were presented for the two methods. Finally, both methods were successfully utilized in determining the fate of the chelates.

Rapid and simultaneous determination of piperidinium and pyrrolidinium ionic liquid cations by ion pair chromatography coupled with direct conductivity detection

A method of ion-pair chromatography with direct conductivity detection was developed on a silicabased monolithic column for the fast and simultaneous determination of piperidinium and pyrrolidinium ionic liquid cations. The effects of the mobile phase, column temperature and flow rate on the retention of the cations were investigated. The retention rules were discussed. As an ion-pair reagent, sodium heptanesulfonate is more suitable than sodium pentanesulfonate for the separation and determination of piperidinium and pyrrolidinium cations. The increase of ion-pair reagent concentration led to the increased retention time of the cations. When acetonitrile content and mobile phase flow were increased, the retention time of the cations became shorter. The retention of piperidinium and pyrrolidinium cations is an exothermic process, and the retention of the cations conforms to the carbon number rule. The chromatographic analysis was performed using the Chromolith Speed ROD RP-18 e column, 0.5 mmol/L sodium heptanesulfonate-5% acetonitrile as the mobile phase at a flow rate of3.0 m L/min and column temperature of 30℃. Separation of N-methyl-N-ethyl piperidinium, N-methylN-propyl piperidinium, N-methyl-N-butyl piperidinium and N-methyl-N-ethyl pyrrolidinium, Nmethyl-N-propyl pyrrolidinium, N-methyl-N-butyl pyrrolidinium cations were achieved within10 min. The detection limits（S/N = 3） were between 0.19 and 3.08 mg/L. Relative standard deviations（n = 5） for peak areas were less than 1.2%. The method has been applied to the determination of piperidinium and pyrrolidinium cations in ionic liquid samples. The spiked recoveries of ionic liquid cations were between 96% and 111%. The method is accurate, reliable, rapid, and has a better practicability.

Novel additives for the separation of organic acids by ion-pair chromatography

This paper proposes the use of novel surfactant additives for the separation of organic acids by ion-pair chromatography and studies the influences of surfactants on the chromatographic separation behaviors.Researches have been carried out on both silica gel matrix and polymer supporters in order to compare the two ordinary kinds of stationary phases,and the phenomenon is similar. Separation is based on differences in the stabilities of analyte-additive complexes in solution.Retention times of analytes can ...

Enantiomeric Separation of Amino Alcohols by Ion-pair Chromatography

Enantiomers of four amino alcohols were resolved by ion-pair chromatography with (+)-10-camphorsulphonic acid as chiral counter ion. Studies of the influence of the mobile phase composition, the solute structure and the mobile phase flow-rate on separation are presented. Under the optimized conditions enantiomeric propanolol, norephedrine, metropolol and salbutamol were separated using dichloromethane-1-pentanol (97:3 v/v) as mobile phase on Lichrospher-100-DIOL column.

Synthesis and Crystal Structure of a Novel Ion-pair Compound Consisting of 1-(4-Bromobenzyl)pyridinium Cation and 7,7,8,8-Tetracyanoquinodimethanide Anion

The title compound [BrBzPy][TCNQ] （BrBzPy^＋=1-（4-bromobenzyl）pyridinium cation, TCNQ = 7,7,8,8-tetracyanoquinodimethanide anion） was synthesized by the reaction of [BrBzPy]Br and LiTCNQ in ethanol solution and its structure was determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c with a = 14.067（3）, b = 7.3089（14）, c = 23.796（4）A, β = 122.011（9）°, V= 2074.6（7）A^3, Z = 4, C24H15BrN5, Mr = 453.32, Dc = 1.451 g/cm^3,μ = 2.002 mm^-1, S = 1.047, F（000） = 916, R = 0.0398 and wR = 0.0921. The most prominent structural features are the completely segregated stacking columns of the TCNQ- anions and [BrBzPy]^＋ cations. In a TCNQ column, the centroid-to-centroid distances of the neighboring anions of TCNQ are 3.2693 and 4.9464 A, respectively.

The Quantum Scattering Study for Ion-pair Formation Reaction Na+I_2→Na^+I_2^- with the LCAC-SW method

The selected-state probabilities of collinear ion-pair formation process Na+I2→Na++I2-on Aten-Laming-Los two-State potential energy surface have been calculated by using LCAC-SW method. The results show that reaction probabilities are oscillatory with collision energy; the threshold energy of this ioniZation reaction is 2.8 ev, which is in modest agreement with experimental result.

Synthesis and Crystal Structure of an Ion-pair Compound: [H_2(teta)]^(2+)·[Ni(CN)_4]^(2-)·2H_2O (teta = Meso-5,7,7,12,14,14-hexamethyl- 1,4,8,11-tetraazacyclotetradecane)

The ion-pair compound [H2（teta）]^2＋·[Ni（CN）4]^2-·2H2O （C20H42N8NiO2, teta = meso- 5,7,7,12,14,14-hexamethyl- 1,4,8,11-tetraazacyclotetradecane） was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P211n with a = 10.0784（10）, b = 9.5411（7）, c = 14.1010（14）А, β= 106.752（2）°, V= 1298.4（2）A^3, Mr = 485.33, Z= 2, De= 1.241 g/cm^3,μ（MoKα） = 0.778 mm^-1 and F（000） = 524. The structure was refined to R = 0.0391 and wR = 0.0870 for 2614 observed reflections with I 〉 2σ（I）. The title compound contains one [Ni（CN）4]^2- anion, one protonated macrocyclic tetraamine cation [H2（teta）]^2＋ and two water molecules. There are multiform hydrogen bonds in the compound to link the different components and stabilize the crystal structure.

Synthesis and Crystal Structure of a Novel Ion-pair Compound Consisting of 1,3-Bis(4-cynobenzyl) Imidazole Cation and 7,7,8,8-Tetracyanoquinodimethanide Anion

A novel compound [（CNBz）2Im]2（TCNQ）3（CH3CN）（（CNBz）2Im = 1,3-bis（4-cyano-benzyl） imidazole cation,TCNQ-1 = 7,7,8,8-tetracyanoquinodimethanide anion） was synthesized by the reaction of [（CNBz）2Im]Br and LiTCNQ in water and its structure was determined by single-crystal X-ray diffraction.The crystal belongs to monoclinic,space group P21/c with a = 10.1823（17）,b = 20.292（3）,c = 16.952（3） ,β = 104.73（0）°,V = 3387.6（10）3,Z = 4,C39H24N11,Mr = 646.69,Dc = 1.268 g/cm3,μ = 0.080 mm-1 and F（000） = 1340.The structure was solved by direct methods and refined to R = 0.0596 and wR = 0.0911 for 2690 observed reflections（Ⅰ 〉 2σ（Ⅰ））.The most prominent structural feature is that there are two types of TCNQ entries（TCNQ-1 and TCNQ0） in agreement with the IR spectra analysis of the compound.

Preparation,Crystal Structure and Density Functional Theory Calculations of the Ion-pair Compound [Cl2Bz(3-MeQl)](TCNQ)

A novel compound [Cl2Bz（3-MeQl） ]（TCNQ） （[Cl2Bz（3-MeQl） ]^＋ = 1-（3,4-dichlo-robenzyl） 3-methlquinoline cation,TCNQ-= 7,7,8,8-tetracyanoquinodimethanide anion） has been synthesized by the reaction of [Cl2Bz（3-MeQl） ]Br and LiTCNQ,and its structure was determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic,space group P21/c. The structure analysis shows that the anions are stacked into a column with isolated π-dimers,and there is one type of TCNQ entries（TCNQ^-） ,in agreement with the IR spectra analysis and density functional theory calculations of the compound. The most prominent structural features are the completely segregated stacking columns of the TCNQ- anions and [Cl2Bz（3-MeQl）]＋ cations.