Triple Ions Research Articles

Microwave Dielectric Relaxation, Electrical Conductance, and Ultrasonic Relaxation of LiPF6 in Poly(ethylene oxide) Dimethyl Ether-500

Microwave dielectric complex permittivity ε* = ε‘ − Jε‘ ‘ in the frequency range ∼1−130 GHz and at temperatures of 25, 40, and 55 °C for the system LiPF6 dissolved in poly(ethylene oxide) dimethyl ether of average molar mass 500 (PEO-500) are reported. The dielectric spectra are interpreted by a Cole−Davidson distribution function for both the solvent and the solutions. The activation parameters ΔH⧧ and ΔS⧧ for the dielectric process have been determined for both solvent and solutions. Audio frequency electrical conductance of solutions of LiPF6 in PEO-500, in the concentration range ∼5 × 10-4 to 1.0 M (M = mol/dm3) and temperatures 25, 40, and 55 °C, have been determined. The conductance data in the diluted range have been analyzed by two forms of the Fuoss-Onsager conductance theory. Despite the presence of a minimum in the conductance vs concentration functions, the presence of conducting triple ions has not been postulated, because the minimum is predicted by the functional form of the conductance theory at low solvent permittivities, for moderate ion-pair associations. Ultrasonic relaxation spectra in the frequency range ∼1 to ∼400 MHz and LiPF6 concentration range 0.1−0.5 M at 25 °C are reported and analyzed in terms of the sum of two debye relaxation processes. The upper one centered around 150−200 MHz and common to the solvent PEO-500 is attributed to polymer-chain rearrangements, also influenced by the presence of the electrolyte. The lower relaxation process in the low megahertz frequency range is interpreted in terms of formation of dimers-ion pairs according to the process 2LiPF6 ⇌ (LiPF6)2, thus rationalizing the presence of a maximum in the static dielectric permitivity vs concentration.

Influence of the Fe 2+ ion triple clusters on the magnetic susceptibility of Fe-based diluted magnetic semiconductors

Low lying energy levels of Fe 2+ ion triples in the cubic-structure iron-based diluted magnetic semiconductors are calculated on the basis of a model which includes crystal field, spin–orbit interaction, Zeeman interaction and Heisenberg-type exchange interaction. Using this energy level diagram the magnetic susceptibility of a crystal is calculated in the nearest-neighbour (NN) and in the extended NN pair approximation. We find that the Fe 2+ ion triples contribute to the temperature dependent susceptibility up to the lowest temperatures investigated, T⩾1 K. It appears that the triple Fe 2+ ion clusters may explain at least a part of the low-temperature increase of the magnetic susceptibility which is observed in these magnetic materials.

Electrical Conductivity and Solubility of KF in N,N-Dimethylformamide up to 125 °C

The solubility of potassium fluoride (KF) in dimethylformamide (DMF) and the dielectric constant of the solvent have been determined in the temperature range (25−125) °C by means of electrical conductivity and capacity measurements. The solubility of KF in this aprotic solvent seems to be almost temperature independent (mean value (0.33 ± 0.03) × 10-3 mol·dm-3). The speciation of KF in DMF is also discussed in relation to the concentration dependence of the molar conductance. It is concluded that ion pairs could account for around 50 to 70% of the species and that triple ions could be present in the concentration range studied.

A Study on the Solvation Phenomena of Some Sodium Salts in 1,2-Dimethoxyethane from Conductance, Viscosity, Ultrasonic Velocity, and FT-Raman Spectral Measurements

Electrical conductances, viscosity, apparent molar adiabatic compressibilities and Fourier transform (FT)-Raman spectra of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), and sodium tetraphenylborate (NaBPh4) in 1,2-dimethoxyethane have been reported. All these electrolytes are found to be strongly associated in this solvent medium. Both ion pairs and triple ions are found to be formed though an overwhelming fraction of each of these electrolytes exists as ion pairs. For NaClO4, the solvent-separated ion pairs predominate over the contact species. For NaBF4 and NaBPh4, on the other hand, the contact species are also formed in significant amounts. FT-Raman studies indicate the presence of “spectroscopically free” ClO4-, BF4-, and BPh4- ions in 1,2-dimethoxyethane solution. The ClO4- ion is found to be significantly solvated, whereas BF4- and BPh4- ions are poorly solvated in DME solution.

A Study of Alkali Halide Triple Ions by Fast Atom Bombardment and Collisionally Activated Dissociation Mass Spectrometry.

This work represents a more precise study of the characteristics of A1XA2+ ions in the gas phase, which can be formed in concentrated electrolyte solutions. In order to obtain the parent ions A1XA2+, a simple system was used, a mixture of two-alkali halide salts in an aqueous solution. In this system, A1+, A2+ are Li+, Na+, K+, Rb+, Cs+ and X- is F-, Cl-, Br-, I-, respectively. Utilizing Fast Atom Bombardment (FABMS) measurement methods, an A1XA2+ ion type in the mass spectra was obtained, and from this resulting spectrum, an ion was selected to be used as a precursor ion for the next stage. In this way, the Collisionally Activated Dissociation (CAD) spectra were obtained and the product ions identified.

Aren-BuLi/TMEDA-Mediated Arene Ortholithiations Directed? Substituent-Dependent Rates, Substituent-Independent Mechanisms

Rate studies of the lithiation of benzene and related alkoxy-substituted aromatics by n-BuLi/TMEDA mixtures implicate similar mechanisms in which the proton transfers are rate limiting with transition structures of stoichiometry [(n-BuLi)2(TMEDA)2(Ar−H)]⧧ (Ar−H = benzene, C6H5OCH3, m-C6H4(OCH3)2, C6H5OCH2OCH3, and C6H5OCH2CH2N(CH3)2). Cooperative substituent effects and an apparent importance of inductive effects suggest a mechanism in which alkoxy−lithium interactions are minor or nonexistent in the rate-limiting transition structures. Supported by ab initio calculations, transition structures based upon triple ions of general structure [(n-Bu)2Li]-//+Li(TMEDA)2 are discussed.

Lithium Diisopropylamide-Mediated Enolizations: Solvent-Independent Rates, Solvent-Dependent Mechanisms

Rate studies of a lithium diisopropylamide-mediated ester enolization reveal solvation effects that are not in accord with expectation. Metalations in THF, t-BuOMe, HMPA/THF, and DMPU/THF (HMPA = hexamethylphosphoramide, DMPU = 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone) occur at nearly the same rates, yet proceed via four fundamentally distinct scenarios: (1) disolvated monomer in THF, (2) monosolvated dimer in t-BuOMe, (3) both monosolvated monomer and tetrasolvated dimer in HMPA/THF, and (4) mono- and disolvated monomers in DMPU/THF. The implication of reactive open dimers in t-BuOMe and triple ions in HMPA/THF underscores the importance of aggregate-based reactions.

Solvation of Li+ by Acetone, THF, and Diethyl Ether in the Gas Phase and the Ion−Molecule Association Mechanism

Fourier transform ion cyclotron resonance spectrometry has been employed to study the solvation of the Li+ ion with acetone, tetrahydrofuran (THF), and diethyl ether (DEE) in the gas phase. LiILi+ triple ions are produced in the ICR cell by the laser desorption ionization of a lithium iodide/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. All O donors abstract Li+ from the triple ion and form solvated complexes with a maximum solvation number of three at room temperature, around 10-6 Torr. All third solvent binding energies are determined from van't Hoff plots. Structures and energetics of the Li+·(S)n complexes, where n = 1−4 for acetone and THF and n = 1−3 for DEE, have been calculated at the Hartree−Fock level with a 6-311+G(d,p) basis set. Solvation enthalpies and free energies are calculated, and solvent binding enthalpies are compared with experiments. The kinetics of solvent exchange and the association reactions of Li+·(acetone-h6)(acetone-d6) with a 1:1 acetone-h6/acetone-d6 mixture have been measured as a function of pressure. The lifetime of the collision complexes are derived and compared with phase space theory calculations. The isotope effect on the radiative cooling rate is discussed.

溶液中のアルカリ金属イオンの化学結合力と溶液内平衡及び反応速度に及ぼす影響

In poor solvating media, unexpected large chemical bonding forces of alkali metal ions, especially Li+, have been revealed. The chemical bonding forces of alkali metal ions and its effects on chemical equilibria and reaction rates in solution are reviewed. The complex formation constants of alkali metal ions with carboxylate ions as well as macrocyclic polyetheramines (L) in acetonitrile were obtained by the analysis of the shift in E1/2 of the mercury-dissolution wave of L. The higher ion aggregation, i.e., the formation of triple ions and quadrupoles, from 1:1 salts in higher permittivity solvents (er>10) was demonstrated by conductometry and spectrophotometry. The salt effects on the indicator acidity in acetonitrile have been attributed to the chemical interaction with the alkali metal ions (M+), alkaline earth metal ions (M2+), or anions. Stable carbocations were produced from (4-methoxy-substituted) trityl halides in acetonitrile, making use of the direct interaction between M+ of M2+ and the halide ions. A mixed-anion salt, BaCl(ClO4), was isolated from acetonitrile solution. The concentrated salt effects on the solvolysis reaction rates of organic halides (RX) in water-mixed solvents have been explained in terms of the direct interaction between M+ or M2+ and X-, and not just of medium effects. Alteration of the bulk water to isolated water molecules in the presence of concentrated salts is proposed.

Aggregation of Ions in Higher Permittivity Solvents

Electrolytic conductances of lithium 4-acyl-5-pyrazolonates (a kind of β-diketonates) and related salts in higher permittivity solvents, acetonitrile (εr = 35.95), acetone (20.7), N,N-dimethylformamide (DMF) (36.71), and propylene carbonate (64.4) were measured at 25 °C. The molar conductivity−concentration (Λ−c1/2) plots of lithium 1-phenyl-3-methyl-4-benzoyl-5-pyrazolonate (LiPMBP) in acetonitrile and acetone display a minimum at 1.51 × 10-3 and 2.0 × 10-3 mol dm-3, respectively, but not in DMF and propylene carbonate. The observed Λ values of LiPMBP in all the solvents are explained by the presence of ion pairs (LiA: A = PMBP) and higher ion aggregates, “symmetrical” triple ions ((Li+)2A-, Li+(A-)2), and quadrupoles (Li2A2). The addition of small amounts of MeOH, H2O, or DMF to acetonitrile caused the cmin value to be higher; with ≥1.0 vol % of these solvents added, the minimum disappeared completely. However, the addition of MeNO2 or PhNO2 caused a more distinct or deeper minimum in the Λ − c1/2 curve. Upon the appearance of the minima, the effects of permittivity and viscosity of the mixed solvents were examined. The conductivity plots of the lithium salts of the 4-trifluoromethoxy derivative (LiPMTFP) and 3-phenyl-4-benzoyl-5-isoxazolonate (LiPBI) did not give minima in the solvents. The observed Λ values could not be fitted without taking into account higher ion aggregations. In DMF, LiPMTFP was much more dissociative. The association constants of the β-diketonates are discussed from the viewpoint of the electron density on the oxygen atoms. Computer calculations indicate that unilateral triple ion formation is impossible for the present system exhibited minima. The formation of bilateral triple ion species (Li+)2A- and Li+(A-)2 (where A- = PMBP- or PBI-) in acetonitrile solution was demonstrated by means of UV−visible and 7Li NMR spectra. The formation of even 5- or 6-coordinated as well as 4-coordinated species was suggested when a large excess of n-Bu4NPBI was present in 0.01 mol dm-3 LiClO4−CD3CN.

Conductometric study of lithium halides and thiocyanate in the mixed solvents of tetrahydrofuran and 2-ethyl-1-hexanol

Ion association constants of lithium chloride, bromide and thiocyanate were evaluated by means of conductometry in the mixed solvents of THF (εr=7.58) and 2-ethyl-1-hexanol (εr=7.58) at 25°C. The mixed solvents were assumed to have a nearly constant permittivity but different solvation abilities. Lithium bromide gave a minimum on the molar conductivity Λ (S cm2 mol−1)−c1/2 curve at a rather low salt concentration (cmin=4.9×10−3 mol dm−3) in THF; however, the cmin increased suddenly to 1.2×10−2 mol dm−3 by the addition of 1.0 vol.% alkanol, and increased gradually by the further addition of the alkanol. The cmin for LiSCN increased gradually with increasing content, up to 30 vol.% of the alkanol. The conductivities of LiBr and LiSCN were analyzed by our method to obtain the formation constants of the ion pair (K1), the triple ions (2Li++X−⇌Li2X+, Li++2X−⇌LiX2−; K2=K3) and the quadrupole (K41) in THF, whereas quadrupole formation constants were not needed for explaining the conductivities in the mixed solvents. In the higher concentration range of LiBr and LiSCN in THF, the ion pair and the quadrupole were found to be the predominant species over the single ions or the triple ions. The increase in cmin with increasing content of 2-ethyl-1-hexanol was in good accordance with the decrease in the formation constants of the higher aggregations. A linear relation (the slope of −1.0) was given between log(K2/K1) and log cmin for LiBr and LiSCN in the binary solvent systems. Lithium chloride gave no minimum, not only in THF but also in the mixed solvents, at least ≤10 vol.% of 2-ethyl-1-hexanol, because of a strong trend to form the quadrupole.

Solvation of the Li+–Cl−–Li+ triple ion in the gas phase

Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry was employed to study solvations of the Li+–Cl−–Li+ triple ion with oxygen-donor Lewis bases in the gas phase. The LiClLi+ triple ions were produced in an ICR cell by laser desorption ionization of a lithium chloride/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. O-donor Lewis bases include 1,4-dioxane, 1,3-dioxane, tetrahydrofuran (THF), acetone and diethyl ether. All O-donors associate directly with LiClLi+ with the maximum solvation numbers of 3 for 1,4-dioxane, 1,3-dioxane and diethyl ether, and 4 for THF and acetone at room temperature. The rate constants for the stepwise solvations were measured, and the solvent binding energies were determined from van’t Hoff plots. The structures and energetics of LiClLi+ and the 1:1 complexes of Li+ and LiClLi+ with the dioxanes, THF, and acetone were calculated at the Hartree-Fock (HF) level with a 6-311G(d,p) basis set, and those of more highly coordinated LiClLi+ complexes were calculated with a 6-31G(d) basis set. Solvation enthalpies and free energies were calculated, and solvent binding energies were compared with experiments. The mechanisms of stepwise solvations of the LiClLi+ triple ion with dioxanes, THF, and acetone are discussed in light of experimental kinetics and binding energies and theoretical structures and solvation energies.

“Non-ergodic” effect of LiCl, n-BuOLi and tert-BuOLi on the anionic polymerization rate of styrene in tetrahydropyran at 20°C

At 20°C in tetrahydropyran, the addition of a molar proportion r of LiCl, n-BuOLi or tert-BuOLi markedly influences the rate constant k 1 of the anionic polymerization of PStLi. However the effect depends on the molar concentration P of the “living ends”. In the range of P = 10 −5 M a decrease of the rate constant is observed which, at r = 5, falls for tert-BuOLi below 30 % of the initial value. But in the range of P = 10 −3 M the addition of LiCl or n-BuOLi produces on the contrary a marked increase of the rate constant compared to the values in absence of additive. These effects are related to the association of the low-molecular additives in THP; for instance LiCl + LiCl ⇔ LiClLiCl. A small part of this process necessarily occurs through the ionic intermediates: Li + + ClLiCl − or Cl − + LiClLi + . In these intermediates LiCl passes continuously from the anion to the cation and vice-versa and, as a consequence, the concentrations of the triple ions are not ruled by the classical mass action law. The participation of Li + in this reversible process competes with its specific interaction with the electron donor sites of the solvent to give LiS 4 + . This effect cannot be treated quantitatively by classical equations but appears to obey “non-ergodic” equations of the thermodynamics of the mobile order and disorder (MOD) based on time fractions. During the period where LiCl is involved in the whole reversible association process, it cannot form LiS 4 + ions and, during the fraction of time it is involved in a reversible formation of LiS 4 + ions, it cannot associate with another LiCl. In the presence of PStLi these molecules replace a part of the LiCl molecules in the associates. These “liberated” LiCl molecules are then not prevented from dissociating in the usual way to give LiS 4 + ions. This phenomenon increases the concentration of Cl − ions in the solution. The quantitative development of the MOD equations leads to the expression: k l k l () = 1+( 3 4 ) q r 2 g P l + r + q r 2 g P l + q r The parameter g can be acquired from conductance data. By adjusting the value of q at 0.03, the calculated values of k l k l agree reasonably with the experimental ones.

Triple Ion Formation in Localized Organolithium Reagents

A variety of aggregation motifs dominate the structural chemistry of organolithium compounds. At least four distinct modes of dimerization exist: the common 4-center dimers,1 6-center dimers as in 2-lithio-2-methyldithiane,2 solvent-bridged dimers as in (LiBr)2‚(HMPA)3, and triple ions (lithium ate complexes) of type R-Li-R-//Li+.5,6a,7 The reactivity of these various dimers compared to monomers or higher aggregates is usually unknown. Triple ions possess an intriguing combination of features of both a dimer and a solvent-separated ion pair. Several lithium amides,8,9a â-keto10 and â-imino9b enolates, and a few other lithium reagents7b have been rigorously shown through crystal structures or NMR data to form triple ions. Delocalized, lithiocene-type sandwich structures are also known;6a,7a however, there is only a single report of a localized carbanion triple ion: a crystal structure was obtained of the triple ion of tris(trimethylsilyl)methyllithium.5 Here, we present NMR evidence that triple ions form in THF/HMPA solution4b for a variety of localized lithiated carbanions, such as aryllithiums and sulfurand silicon-substituted alkyllithiums.

Evidence for ion pairs and/or triple ions from transport measurements in mixed-alkali polyether electrolytes

This work concerns amorphous poly(ethylene oxide) (PEO) rubbery electrolytes with new lithium salts, LiN(CF 3CO) 2 and Li[CF 3SO 2N(CH 2) 3OCH 3] (LiMPSA), which contain carbonyl or ether groups in their anions. Although these salts are markedly less conductive than LiN(CF 3SO 2) 2 or LiClO 4, one of them (LiMPSA) yields a large fraction of a species that promotes lithium transport through back diffusion under polarization in Li/PEO–LiX/Li symmetrical cells. Polarization experiments carried out on similar cells filled with PEO–LiX–KX, mixed-alkali electrolytes show that this species is a LiX − 2 complex of lower mobility than Li + in PEO. In turn, these experiments reveal that LiN(CF 3CO) 2 yields a large fraction of LiX ion pairs more mobile than Li + in PEO. These features, which are founded on theoretical models for polarization of PEO–LiX–KX electrolytes between lithium electrodes, agree with other properties (T g elevation and conductivity) of the present systems.

Formation of separated versus contact ion triples in heavy alkaline-earth thiolates

The synthesis and structural characterization of the alkaline-earth thiolates [Sr(18-crown-6)(hmpa)2][SMes*]2 and [Ba(18-crown-6)(hmpa)(SMes*)][SMes*], displaying rare ion association modes with only one or no cation–thiolate linkages are presented.

Relationship between Triple Ion Formation Constants and the Salt Concentration of the Minimum in the Conductometric Curves in Low-Permittivity Solvents

Conductivities of a number of uni-univalent salts, including tetrabutylammonium and lithium nitrophenolates, were measured at 25.0 °C in low-permittivity solvents such as tetrahydrofuran (THF, εr = 7.58), 1,2-dimethoxyethane (DME, 7.2), chloroform (4.8), and ethyl acetate (6.0). Minima in the conductometric curves (Λ−C1/2) were observed for concentrations which were dependent upon both the salt and the solvent, Cmin = 1.73 × 10-4 mol dm-3 for 2,4-(NO2)2C10H5OLi (lithium 2,4-dinitro-1-naphtholate) in THF and 2.56 × 10-2 mol dm-3 for LiPic (lithium picrate) in DME. The observed molar conductivities including Cmin could be completely explained by the formation of ion pairs (M+ + X- ⇌ MX, K1), “symmetrical” triple ions (2M+ + X- ⇌ M2X-, K2; M+ + 2X- ⇌ MX2-, K3; K2 = K3), and (in some cases) additional formation of quadrupoles (2MX ⇌ M2X2, K41). A linear relationship (the slope of −1) between the triple ion formation constants (log(K2/K1)) and the salt concentrations at the minimum (log Cmin) was given for all the salts in the various solvents, except for some systems in which a distinct formation of quadrupole takes place, e.g., LiNO3 in DME (K1 = 3.16 × 1010, K2 = 4.5 × 1013, and K41 = 35). The formation of triple ions might be attributed to the ion sizes in solutions in which Coulombic interactions were the only main forces between ions (R4N+···X-). However, coordination (or covalent) bonding forces as well as Coulombic forces had to be considered for the lithium salts except for LiClO4 and LiBF4). Gutmann's donor and acceptor numbers of solvents (and not the permittivity) accounted for the larger difference of Cmin of lithium salts in THF and DME. In mixed solvents of THF and 2-ethyl-1-hexanol (εr = 7.58), the Cmin values of LiNO3 and 2,4-(NO2)2C10H5OLi increased with increasing contents of the hexanol, whereas the Cmin values of LiClO4 and Bu4NX (X- = NO3-, 2,4-(NO2)2C10H5O-, and ClO4-) remained constant for 0−30 vol % hexanol added to THF. The positive shifts in Cmin were explained quantitatively by the decrease in triple ion formation constants and/or by an increase in the quadrupole formation constants.

Solvation of the Li+−Br-−Li+ Triple Ion in the Gas Phase

The solvation of the Li+−Br-−Li+ triple ion with oxygen-donor Lewis bases was studied in the gas phase with use of Fourier-transform ion cyclotron resonance spectrometry. The Li+−Br-−Li+ triple ions were prepared in an ICR cell by matrix-assisted laser desorption ionization of a lithium bromide/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. The stepwise solvations of LiBrLi+ were examined with oxygen-containing Lewis bases: 15-crown-5-ether (15C5), 12-crown-4-ether (12C4), 1,4-dioxane, 1,3-dioxane, and tetrahydrofuran (THF). Crown ethers solvate Li+ with loss of LiBr. 15-Crown-5-ether yields a 1:1 (15C5)·Li+ complex as the end product, whereas 12-crown-4-ether forms a 2:1 (12C4)2·Li+ complex. On the other hand, low dielectric constant solvents, such as dioxanes and THF, solvate the Li+−Br-−Li+ triple ion rather than abstracting Li+ with loss of the neutral ion pair. The maximum coordination numbers are 3 for dioxanes and 4 for THF at 293 K. The rate constants for the stepwise solvations we...

Ionization conditions for iontophoretic drug delivery. Electrical conductance and aggregation of lidocaine hydrochloride in 1-octanol at 25°C

The behaviour of lidocaine hydrochloride (LidH+Cl−) in 1-octanol at 25.00°C has been studied with respect to transport properties and aggregation by precision conductometry over the concentration interval 0.2–6 mM. The analysis of the conductance data, based on the conductance equation of Fuoss, Hsia, and Fernandez-Prini (FHFP equation), indicates that for concentrations up to 0.6 mM free LidH+ and Cl− ions are present in equilibrium with LidH+Cl− ion pairs. At higher concentrations there is strong evidence of formation of (LidH)2Cl+ and LidHCl2− triple ions. Any dissociation of LidH+ into Lid and H+ is shown to be negligible within the concentration interval studied. The values Ka=(127.6±2.7)·103 and KT=65 of the ion pair and triple ion association constants, respectively, were obtained. The limiting molar conductivity, Λ0(LidHCl)=1.969±0.031 cm2 Ω−1 mol−1, is less by a factor of about 50 as compared with the corresponding value for water as solvent medium. This effect can be only partly ascribed to the difference in viscosity between 1-octanol and water. The mobility of the triple ions is found to be 1/3 of that of the free ions.

Dual influence of lithium chloride on the reactivity of polystyryllithium in ethereal solvents

AbstractAddition of LiCl to ethereal solutions of polystyryllithium retards propagation of the polymerization at low polymer concentration, but accelerates it at higher polymer concentrations. This phenomenon is accounted for by the dual action of LiCl. Its dissociation yielding free common Li+ ions which diminish the concentration of the reactive free polystyryl anions dominates at low electrolyte concentrations. However, at their higher concentrations the Li+ scavenging action of LiCl, resulting in the formation of LiClLi+ triple ions, becomes important, it reduces the concentration of the free Li+ ions and increases, therefore, the proportion of the reactive free polystyryl anions.