Sodium Ion Pairs Research Articles

A Raman spectroscopic and ab initio investigation of aqueous boron speciation under alkaline hydrothermal conditions: evidence for the structure and thermodynamic stability of the diborate ion.

Raman spectra of aqueous sodium borate solutions, with and without excess NaOH, NaCl, and LiCl, have been obtained from perpendicular and parallel polarization measurements acquired using a custom-built sapphire flow cell over the temperature range 25 to 300 °C at 20 MPa. The solvent-corrected reduced isotropic spectra include a large well-defined band at 865 cm-1 which overlaps with the boric acid B(OH)3 band at 879 cm-1, and becomes increasingly intense at elevated temperatures. This band does not correspond to the spectrum of any other previously reported aqueous polyborate ions, all of which have symmetric stretching bands at frequencies below that of borate, [B(OH)4]-, at 745 cm-1. Based on the classic high-temperature potentiometric titration study by R. E. Mesmer, C. F. Baes and F. H. Sweeton, Acidity measurements at elevated temperatures. VI. Boric acid equilibriums, Inorg. Chem., 1972, 11, 537-543, the new band was postulated to arise from a diborate ion, [B2(OH)7]- or [B2O(OH)5]-. Ab initio density functional theory (DFT), together with chemical modelling studies, suggest that it is most likely [B2(OH)7]-. Thermodynamic formation quotients derived from the peak areas showed variations with ionic strength as well as charge-balance discrepancies, which suggest one or more unidentified minor equilibrium species may also be present. The most likely candidate is the divalent diborate species [B2O2(OH)4]2- which is also predicted to have a band near 865 cm-1 and is postulated to be present as a sodium ion pair. These are the first quantitative Raman spectra ever reported for borate-rich solutions under such conditions and provide the first spectroscopic evidence of a diborate species at PWR reactor coolant temperatures.

Understanding supercooling mechanism in sodium sulfate decahydrate phase-change material

Salt hydrate-based phase-change materials are considered promising for future heat storage applications in residential heating/cooling systems. Smooth phase transition from the liquid to solid phase and vice versa is essential for effective heat exchanger; however, supercooling in salt hydrates delays the onset of liquid–solid phase transition. We investigate the molecular level mechanism of supercooling in sodium sulfate decahydrate (SSD). SSD is a complex salt hydrate whose properties are governed by electrostatic forces that include pure Coulombic interactions as well as hydrogen bonds. Experimentally, we examine the importance of a nucleator in reducing supercooling temperatures. We investigated the effect of various mass concentrations of a borax nucleator on a decrease of supercooling temperatures. Molecular dynamics simulation techniques are used to obtain a basic understanding of supercooling in SSD. We observe that by introducing borax as a nucleator, there is a decrease in the supercooling temperature before nucleation. Our molecular dynamics simulations show that long-range electrostatics between sodium and sulfate ion pairs and that with polar water molecules is responsible for delayed nucleation in SSD that results in supercooling, and also, dynamics of charged molecules slows down. The lack of crystallization leads to amorphous structures in supercooled SSD.

Identification of Ion-Pair Structures in Solution by Vibrational Stark Effects

Ion pairing is a fundamental consideration in many areas of chemistry and has implications in a wide range of sciences and technologies that include batteries and organic photovoltaics. Ions in solution are known to inhabit multiple possible states, including free ions (FI), contact ion pairs (CIP), and solvent-separated ion pairs (SSIP). However, in solutions of organic radicals and nonmetal electrolytes, it is often difficult to distinguish between these states. In the first part of this work, we report evidence for the formation of SSIPs in low-polarity solvents and distinct measurements of CIP, SSIP, and FI, by using the ν(C≡N) infrared (IR) band of a nitrile-substituted fluorene radical anion. Use of time-resolved IR detection following pulse radiolysis allowed us to unambiguously assign the peak of the FI. In the presence of nonmetal electrolytes, two distinct red-shifted peaks were observed and assigned to the CIP and SSIP. The assignments are interpreted in the framework of the vibrational Stark effect (VSE) and are supported by (1) the solvent dependence of ion-pair populations, (2) the observation of a cryptand-separated sodium ion pair that mimics the formation of SSIPs, and (3) electronic structure calculations. In the second part of this work, we show that a blue-shift of the ν(C≡N) IR band due to the VSE can be induced in a nitrile-substituted fluorene radical anion by covalently tethering it to a metal-chelating ligand that forms an intramolecular ion pair upon reduction and complexation with sodium ion. This adds support to the conclusion that the shift in IR absorptions by ion pairing originates from the VSE. These results combined show that we can identify ion-pair structures by using the VSE, including the existence of SSIPs in a low-polarity solvent.

Evaluation of the Hydrophilic Property of Sodium Ion-pair Complexes with 3m-Crown-m Ethers (m = 5, 6) and Their Benzo-derivatives by Solvent Extraction

The ion-pair formation constants {K(j)(0): j = MA (metal salt), MLA} of NaO(2)CCF(3) (Na(+)tfa(-)) and its ion-pair complexes (MLA) in water (w) were determined potentiometrically at 25 degrees C and an ionic strength (I) of zero. 15-Crown-5 (15C5), 18-crown-6 ethers (18C6), and their mono-benzo derivatives were used as crown ethers (L). The extraction of Natfa by these four L from w into 1,2-dichloroethane was done at 25 degrees C, and then the extraction constants (K(ex)) for NaLtfa were calculated by using the K(j) values, which were estimated from the corresponding K(j)(0) ones at I of the w-phases, and other equilibrium constants. Also, the distribution constants (K(D,MLA)) of NaLtfa between the two phases were obtained from a thermodynamic cycle expressing K(ex). An interaction of w-molecules with NaLA was considered using a relation of log K(D,MLA) with log K(D,L), derived from the Scatchard-Hildebrand equation, where K(D,L) denotes the distribution constant of L between the two phases. The interaction increased in the order of NaL (picrate) < free L </= NaLMO(4) (M = Mn, Re) < NaLtfa for L = 15C5 and 18C6.

The coordination properties of aminobenzoate ligands in complexes with alkali metals

The crystal structures of sodium 4-amino-2-hydroxybenzoate dihydrate [NaL·2H2O, L = C6H3(NH2)(OH)COO] and potassium 2-aminobenzoate monohydrate [KL*·H2O, L* = C6H4(NH2)COO] were determined by X-ray diffraction methods. The compound NaL·2H2O crystallizes in the monoclinic system, space group P21/c with a = 8.820(2), b = 14.632(3), c = 6.948(2) Å, β = 97.88(3)°. The structure consists of sodium ion pairs joined together by tridentate 4-amino-2-hydroxybenzoate moieties creating a polymeric chain. In the metal centres, two water molecules bridge the sodium atoms. Five oxygen atoms and one nitrogen atom form a distorted octahedral environment. The compound KL*·H2O crystallizes in the monoclinic system, space group P21/c with a = 14.684(3), b = 7.618(2), c = 7.512(2) Å, β = 96.95(3)°. The structure consists of octacoordinated potassium atoms bonded with three water molecules and five carboxylate oxygen atoms. Water molecules appear as bridging ligands. The 2-aminobenzoate ligand acts as a pentadentate ligand with the molecular network stabilized by hydrogen bonds. Among the polymeric chains in both structures appear noncovalent interactions of type N−H···X.

Potassium and sodium chloride ion pairs are presumed to constitute a complex during elution from a Sephadex G-15 column with sodium phosphate buffer

When a mixed solution of 0.72 M potassium and sodium chloride was eluted from a Sephadex G-15 column with 0.025 M sodium phosphate buffer (pH 7.0), the elution profiles of ions showed that the potassium and chloride ion pair from the sample and the sodium and chloride ion pair produced by ion-exchange reaction, were eluted in the same fractions as if they constituted a complex. When a mixed solution of different concentrations of potassium and sodium chloride was eluted with the same buffer, the excess amount of one ion pair over the other was eluted freely from the presumed complex.

Synergistic pseudo-hydroxide extraction: synergism and anion selectivity in sodium extraction using a crown ether and a series of weak lipophilic acids.

The nature of the weak lipophilic acid used in synergistic combination with a model crown ether cation host was shown to have a strong effect on the strength and selectivity of sodium hydroxide separation from alkaline aqueous salt solutions. Sodium ion-pair extraction employing only cis-syn-cis-dicyclohexano-18-crown-6 (1) in nitrobenzene (NB) was correlated with the standard Gibbs energy (deltaG(p)o) of anion partitioning into NB and was notably weak and nonselective for the hydroxide ion, in accord with Hofmeister bias. The Hofmeister order can be selectively overcome for NaOH by utilization of acid-base chemistry coupled with complexation of sodium ion in the NB phase. Upon addition of a lipophilic organic acid into the solution of 1 in NB, sodium extraction was selectively enhanced due to the initiation of an exchange reaction between the aqueous sodium ion and the ionizable proton of the organic acid. A series of weak lipophilic hydroxy acids (HA) including fluorinated alcohols and phenols was tested. The resulting synergistic pseudo-hydroxide extraction correlates with the pKa of the employed HA; the most acidic cation exchangers provide the greatest synergism. The synergistic factor obtained using a fluorinated benzyl alcohol 7 was as high as 256. Ion-pair extraction of neutral sodium salts was not changed or only mildly enhanced by addition of HA into the NB solution of 1. This enhancement was explained by hydrogen bonding of HA with the anion as related to the hardness of the anion and the acidity of HA. In comparison with the synergism observed for NaOH, this enhancement was weak and unable to overcome the Hofmeister effect. Examination of extraction selectivity revealed that the combination of 1 and 7 preferentially extracted NaOH over all other sodium salts, including the normally preferred nitrate and perchlorate salts. Quantitative recovery of NaOH from the NB phase was demonstrated via hydrolysis of the organic acid upon a single contact of the loaded solvent with water.

Correlation between dielectric constant and chemical structure of sodium silicate glasses

The chemical structure of sodium aluminosilicate glasses is determined by high resolution x-ray photoelectron spectroscopy (XPS) as silicon is gradually replaced by aluminum. A well-defined chemical state is found for silicon, aluminum, and sodium atoms, while three different environments are identified for oxygen atoms corresponding to Si–O–Si, Si–O–Al, and Si–O–Na bonds. The binding energy of Na 1s photoelectrons increases significantly with increasing aluminum substitution while that of Al 2p and components of O 1s photoelectrons remains approximately constant. Thus, the ionicity of sodium increases with aluminum amount, but the over all electron density around silicon, aluminum, and different types of oxygen atoms remains unchanged. The dielectric constant of the glasses increases with increasing aluminum substitution. It is analyzed in terms of the polarizabilities of constituent structural units, viz., silicon tetrahedra, nonbridging oxygen–sodium ion pairs, and aluminum tetrahedron–sodium ion pairs. The electronic polarizability of oxygen ions depends linearly on their negative charge and can be correlated to the O 1s XPS binding energy. The ionic polarizability of sodium ions increases with an increasing aluminum amount, and correlates directly with the Na 1s XPS binding energy.

Stereochemistry of metalated aldimines. 1. An ab initio study of the potential energy surfaces of isolated acetaldimine anions, their monomeric lithium and sodium ion pairs, and mechanistic consequences

Stereochemistry of metalated aldimines. 1. An ab initio study of the potential energy surfaces of isolated acetaldimine anions, their monomeric lithium and sodium ion pairs, and mechanistic consequences

Isotropic and solid-state esr spectra of the radical ion pairs of 2,4,6-Tri- tert-butyl thiobenzaldehyde

The sodium and potassium radical ion pairs of 2,4,6-tri- tert-butyl thiobenzaldehyde and of its ring-deuterated analog have been generated in ethereal solutions and studied by means of electron spin resonance spectroscopy. From the magnitude of the 13C hyperfine splitting it has been inferred that in this radical anion the deviation of the aromatic ring from coplanarity with the CHS plane is smaller than that in the diamagnetic precursor. The solid-state spectrum of the deuterated species has also been interpreted and the g and proton hyperfine tensors have been determined.

Zone formation in ion-pair RPLC I. Effects of adsorption of organic ions on established column equilibria

Adsorption of organic ions to μBondapak Phenyl from a water-based mobile phase was studied by the breakthrough technique. The adsorption of decanesulfonate as sodium ion pair as well as of an organic cation, dimethylprotriptyline, as phosphate ion pair was best fitted to a two-site ion-pair adsorption model of the Langmuir type indicating a heterogenous solid phase surface. Introducing an organic ion into a column in equilibrium with an organic ion of opposite charge created negative zones due to increased adsorption of the second ion. The positions of the beginning and the end of the zone were dependent of the concentrations of the two organic ions in the system.

A quantitative approach to the determination of drug release from reverse-phase evaporation lipid vesicles. The influence of sodium ion-pair formation on warfarin partitioning and permeability

The influence of sodium ion-pair formation on warfarin partitioning and permeability has been investigated using reverse-phase evaporation lipid vesicles. An experimental method for the isolation of the vesicles having known amounts of encapsulated drug has been described. The partitioning of warfarin between phospholipid membrane and aqueous phase at different Na + concentrations was determined in separate experiments. Thus, using a two-compartment cylinder assembly the influence of Na + concentration on the release rate of the encapsulated warfarin from the vesicles could be measured quantitatively. It appears that under the present experimental conditions warfarin partitioning does depend on Na + concentration whereas vesicle permeability towards warfarin does not seem to be affected.

Evidence of an enhanced diffusion process in electron-irradiated glasses: a critical analysis of available experimental and theoretical results

Previously reported experimental results on the Na Auger signal decay that occurs during electron irradiation of soda-silica glasses, at liquid nitrogen temperature, have been interpreted on the basis of a numerical integration of the continuity equation for the ordinary and field-assisted diffusion processes. In this context, it is shown that the diffusion process of Na is stimulated by the electron irradiation. It is suggested that the diffusion process is enhanced by oxygen- and sodium-ion pairs being created by bond breaking when electrons strike soda-silica glasses. This phenomenon occurs not only at the surface, as some previous work has suggested, but also in the bulk. Moreover, some critical remarks about previous theoretical models concerned with the incubation time, during which the Auger signal remains constant, are also reported.

Vibrational study of ionic association in aprotic solvents. 6. Dimerization of lithium, sodium, and potassium isothiocyanate ion pairs in tetrahydrofuran and in 1,3-dioxolane

Vibrational study of ionic association in aprotic solvents. 6. Dimerization of lithium, sodium, and potassium isothiocyanate ion pairs in tetrahydrofuran and in 1,3-dioxolane

Influence of sodium ion-pair formation on transport kinetics of warfarin through octanol-impregnated membranes.

Influence of sodium ion-pair formation on transport kinetics of warfarin through octanol-impregnated membranes.

ChemInform Abstract: SODIUM ION PAIR AGGREGATES IN AMINE SOLUTIONS

Chemischer InformationsdienstVolume 14, Issue 1 Physical Inorganic Chemistry ChemInform Abstract: SODIUM ION PAIR AGGREGATES IN AMINE SOLUTIONS C. DETELLIER, C. DETELLIERSearch for more papers by this authorA. GERSTMANS, A. GERSTMANSSearch for more papers by this author C. DETELLIER, C. DETELLIERSearch for more papers by this authorA. GERSTMANS, A. GERSTMANSSearch for more papers by this author First published: January 4, 1983 https://doi.org/10.1002/chin.198301003Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue1January 4, 1983 RelatedInformation

An investigation of the vanadium(V)octacyanomolybdate(VI) reaction

The rapid oxidation of Mo(CN) 4- 8 by VO + 2 was studied in acidic perchlorate media by the use of stopped-flow spectrophotometric techniques. Using a large excess of VO + 2, the formation of Mo(CN) 3- 8 was described by the expression (A∞ − A t = B oe −k ft + P oe −k st and the two reaction pathways at constant [H +] showed a simple first order dependence upon both reactants. Variation of the [H +] demonstrated the direct involvement of one proton in each pathway. The experimental data suggest the reaction of sodium ion pairs of Mo(CN) 4- 8 with VO + 2. Relative rate studied indicate that the faster reaction is of an outer-sphere type.

Influence of ionization and ion-pair formation on lipophilicity of some 4-hydroxycoumarin derivatives in the octanol-water system

The pH-dependent distribution of weak acids in the octanol-water system was investigated. For a series of six 4-hydroxycoumarins, substituted at position 3, the apparent partition coefficient or the distribution coefficient, P app, was measured in the pH range 1–11. The log P app-pH profiles obtained are in complete agreement with the theory. At high pH the value of P app is independent of pH, but dependent on the concentration of counterions (Na + in this study) in the aqueous phase; in other words ion-pair extraction occurs. The pNa (—log [Na +])-dependent distribution is analogous to the pH-dependent distribution, except in the case of 4-hydroxy-coumarin. Evidence was found that the sodium ion-pair of 4-hydroxycoumarin dissociates considerably in the octanol phase. A large discrepancy was noted between the experimentally obtained log P values and the theoretical values calculated using the hydrophobic fragmental constant system. Log P app values obtained under conditions where the compounds are ionized in the aqueous phase depend on both the partition coefficient and the dissociation constant of the acid or salt. Partition coefficients of the sodium ion-pairs obtained by extrapolation are just slightly lower than the partition coefficients of the undissociated acids.

Kinetics of the reaction of poly(α‐methylstyryl sodium, potassium, and cesium) with t‐butyl chloride in tetrahydrofuran

AbstractThe kinetics of the reaction of “living” poly(α‐methylstyrl sodium, potassium, and cesium) with t‐butyl chloride have been studied spectrophotometrically in tetrahydrofuran (THF) in the temperature range 283–303 K. The reactions, when the free ions present in solution are suppressed by tetraphenylboron salt, are first order with respect to both living ends and halide concentrations. Additions of tetraphenylboron salts produce a slight retardation effect on the rate of reaction in the case of sodium, indicating only a small contribution of free ions to the overall rate; in the case of potassium, there is no apparent effect. Analysis of the data indicates that the free ion is approximately 30 times more reactive than the sodium ion pair. The Arrhenius plots for contact ion‐pair termination are linear and the activation energies and preexponential factors determined are E = 38.6 kJ mole−1, log A = 4.44 liter mole−1 sec−1 and E = 46.0 kJ mole−1, log A = 5.10 liter mole−1 sec−1. The reaction mechanism is interpreted in terms of elimination plus some side reaction to produce two unexpected reaction products—isobutane and a 315–320‐nm absorbing grouping in the polymer.

Solvent Induced Structural Change of 18-Crown-6 Complexed Ion Pair with 9-Fluorenone Anion Radical as Studied by ESR Spectroscopy

Abstract ESR spectra of the ion pairs of the 9-fluorenone anion radical with 18-crown-6 complexed sodium and potassium ions were examined. From the dependence of the carbonyl 13C hyperfine splitting of the fluorenone anion on temperature and solvent, it was conclude that an ethereal solvent molecule can solvate the crown complexed cation on the opposite side of the anion with respect to the plane of the crown ether ring, equilibrium taking place between the solvated and unsolvated ion pairs in ethereal solution. The unsolvated species of both the potassium and the sodium ion pairs and the solvated species of the sodium ion pair are classified as contact ion pairs, the solvated species of the potassium ion pair a crown separated one. The equilibrium constant between the solvated and unsolvated ion pairs changes with temperature and solvent. From this change the enthalpy changes of solvation process were estimated for several solvents.