Complexation of alkali metal cations by calix[4]Arene-bis-crown-6 in methanol,acetonitrile and propylene carbonate

Résumé The interactions of Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ with the double-crown calix, calix[4]arene-bis-crown-6, have been studied in methanol, acetonitrile, and propylene carbonate at 25°C using precise conductivity measurements. For Li⁺ and Na⁺ in solutions containing this calix[4]arene, only 1:1 cation:ligand complexes are formed which permit the determination of the thermodynamic complexation formation constants,K _f. The conductivity data strongly suggest that 2:1 cationcalixarene complexes form with K⁺, Rb⁺, and Cs⁺. The existence of 2:1 complexes was experimentally confirmed for the potassium systems by a mass spectroscopic method.     

Thermodynamics of Complexation Reactions of Lithium Ion with Dibenzo-14-Crown-4 and Its Analogs in Nonaqueous Solvents

Formation constants of Li⁺ complexes with 4-substituted dibenzo-14-crown-4 (DB14C4; 4-substituted group: methyl-, tert-butyl-, H-, bromo-, chloro-, formyl-, nitro-) ligands were determined by ⁷Li NMR spectrometry for solutions in nitromethane (NM), acetonitrile (ACN), propylene carbonate (PC), acetone (AC), Pyridine (Py), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and N,N′-dimethyl formamide (DMF). Only a 1:1 complex was formed in solvents with a small or medium donor number. The formation constants of these complexes are strongly influenced by the size of the metal ion – the effect of the size of the cavity, by the solvent and by substituent. The stability of lithium ion with different substituents on DB14C4 decreases in the order methyl- > tert-butyl- > H- > bromo- > chloro- > formyl- > nitro- in various solvents. A good Hammett correlation was found by plotting log K_f vs. ∑σ in PC and AC. The extent of the substituent effect increases as the donor number of solvent decreases. The complexes were both enthalpy and entropy stabilized. The same magnitude of ΔS° value for different substituents indicates formation with a similar configuration upon complexation between crown ether and lithium ion. A slight variation in entropy contribution was observable depending on the nature of the alkyl substituent, whereas a large variation in enthalpic contribution shows a remarkable substituent effect upon complexation; the effect can reach 70% in magnitude.     

Interactions Between Tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane and Perchlorate Anion in Propylene Carbonate, Nitromethane, Acetonitrile, and Tetrahydrofuran

Electrical conductance measurements are reported for lithium perchlorate andthe anion receptor tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane(TTCD) in different aprotic solvents (propylene carbonate, nitromethane,acetonitrile, and tetrahydrofuran). The data have been analyzed by a suitablemethod based on the Lee-Wheaton theory on mixed electrolytes in order to obtainthe true thermodynamic formation constants of macrocyclic-anion complexes andthe ion pairs of both the uncomplexed (ClO₄ ^–)and complexed (TTCD-ClO₄ ^–)anions. The results show that the anion-ligand formation constants increase withdecreasing dielectric constant and that the presence of the ligand increases theionization of lithium perchlorate and enhances the transference number of lithiumion. These findings are of particular interest in view of the technologicalapplication of anion receptors in electrolyte solutions for lithium batteries.     

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.     

Transient natural convection induced by electrodeposition of Li+ ions onto a lithium metal vertical cathode in propylene carbonate

Transient natural convection caused by Li⁺ electrodeposition at constant current along a vertical Li metal cathode immersed in a 0.5 M LiClO₄–PC (propylene carbonate) electrolyte was compared with that by Cu²⁺ ion electrodeposition in aqueous CuSO₄ solution. The concentration profile of the Li⁺ ions was measured in situ by holographic interferometry. The interference fringes start to shift with time at a higher current density. The concentration boundary layer thickness for Li⁺ ions was successfully determined. With the progress of electrodeposition, the density difference between the electrolyte at the cathode surface and the bulk electrolyte increased to induce upward natural convection of the electrolyte. The electrolyte velocity was measured by monitoring the movement of tracer particles. The measured transient behavior of the ionic mass and momentum transfer rates normalized with respect to the steady-state value was numerically analyzed. Transient natural convection along a vertical cathode due to Li metal electrodeposition can be reasonably explained by boundary layer theory, similar to the case of Cu electrodeposition in aqueous CuSO₄ solution.     

Theoretical study on thermochemistry of solvated lithium-cation with propylene carbonate

We report the theoretical analysis results of thermochemical properties of solvated Li⁺ ion in propylene carbonate (PC), which is one of the most popular solvents used in the lithium-ion battery composite. In the theoretical calculation, we employed the density functional theory method with the 6-31G basis set using the Gaussian03 package. It has been made clear that the solvation with four PC molecules around a Li⁺ ion is most favorable. Detailed results of the conventional quantum chemical analyses for these materials will also be presented. Thermochemical properties such as the standard (that is at 298.15 K and 101325 Pa) enthalpy, entropy, and Gibbs energy changes upon the formation of Li⁺ complexes solvated with PC molecules have been numerated and discussed. Furthermore, we will afford the features of desolvation of the solvated Li⁺ ion complexes when they interact with the carbon electrode modeled by ovalene molecules.     

Robust Inclusion Complexes of Crown Ether Fused Tetrathiafulvalenes with Li+@C60 to Afford Efficient Photodriven Charge Separation

Inclusion complexes of benzo‐ and dithiabenzo‐crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li⁺@C₆₀ ( 1? Li⁺@C₆₀ and 2? Li⁺@C₆₀). The strong complexation has been quantified by high binding constants that exceed 10⁶ M ^?1 obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6‐311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li⁺ have a crucial role in robust complex formation. Interestingly, complexation of Li⁺@C₆₀ with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding ³(Li⁺@C₆₀)*, when no charge separation by means of ¹Li⁺@C₆₀* occurs. Photoinduced charge separation by means of ³Li⁺@C₆₀* with lifetimes of 135 and 120 μs for 1? Li⁺@C₆₀ and 2? Li⁺@C₆₀, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time‐resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron‐transfer events in the corresponding complex.     

Paramagnetic probe for molecular interactions: I. EPR and electronic absorption studies of lithium cation solvation by a nitroxide radical

The 2,2,6,6-tetramethylpiperidine nitroxide radical (TMPN) was studied by EPR and electronic absorption spectroscopy in LiClO₄ solutions in various organic solvents. The¹⁴N hyperfine structure, together with the exchange broadening of its components in EPR and the electronic n^* transition in the visible region, provide useful information about Li⁺-TMPN complexes. Both spectroscopic methods prove that the oxygen atom of TMPN was involved in the Li⁺-TMPN interaction. The complex formation constants 15.61, 2.50, 0.75, 0.61, 0.75, and 0.33 dm³-mol^–1 were found in nitromethane, benzonitrile, acetonitrile, propylene carbonate, acetone and tetrahydrofurane, respectively. These formation constants were correlated with donor and acceptor numbers of the solvents and interpreted in terms of competitive Li⁺-TMPN, solvent-Li⁺, and solvent-TMPN interactions.     

Effect of adding ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate on the coordination environment of Li<Superscript>+</Superscript> ions in propylene carbonate,according to data from IR spectroscopy and quantum chemical modeling

The effect ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate has on the coordination environment of Li⁺ cations in carbonate solvents is studied by means of IR spectroscopy and quantum chemical modeling using the example of propylene carbonate (PC). LiBF₄ is used as the lithium salt. This system is promising for use as an electrolyte in lithium power sources (LPSs), but the mechanism of ionic conductivity by Li⁺ ions in such systems has yet to be studied in full.     

Solvation environment of lithium ion in a LiBF<Subscript>4</Subscript>–propylene carbonate system in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid studied by NMR and quantum chemical modeling

Solutions of lithium and 1-ethyl-3-methylimidazolium tetrafluoroborates ([emim][BF₄]) in propylene carbonate (PC) were studied by the high-resolution NMR method on ¹H, ⁷Li, ¹¹B, ¹³C, and ¹⁹F nuclei. The degree of solvation of lithium ions was determined by measuring selfdiffusion coefficients by pulse-field-gradient spin echo NMR method on ¹H, ⁷Li, and ¹⁹F nuclei. The hydrodynamic radii of solvated Li⁺ cations were estimated by the Stokes–Einstein equation. The model structures of the solvation complexes of Li⁺ ion with propylene carbonate molecules and BF ₄ ^– anion and their associates with ionic liquid components were calculated in terms of the density function theory. The calculated values of the chemical shifts were compared with the experimental data. PC molecules were predominantly bound to the Li⁺ cation, while LiBF₄–[emim][BF₄]–PC (1: 4: 4) electrolyte had a maximum conductivity of 9.5 mS cm^–1 at 24 °С compared to the compositions of a lower content of the solvent.     

A Vibrational Spectroscopic Study of Ion Solvation in Lithium Perchlorate/Propylene Carbonate Electrolyte

Abstract

The infrared (IR) and Raman spectra of propylene carbonate (PC) containing various concentrations of LiClO₄ have been measured and analyzed. The difference in spectra of PC with and without LiClO₄ was attributed to the interaction of the PC molecules and lithium ions. This interaction occurs mainly on the carbonyl oxygen atom of the PC molecule. The ring deformation, symmetric ring deformation, carbonyl stretching and stretching of ring oxygens for PC are sensitive to this interaction. The solvation number of Li⁺ is also calculated. On the other hand, the structure of the ClO^? ₄ is also affected by PC molecule, forming the solvent separated ion pairs.     

Unveiling the Critical Role of Ion Coordination Configuration of Ether Electrolytes for High Voltage Lithium Metal Batteries

Albeit ethers are favorable electrolyte solvents for lithium (Li) metal anode, their inferior oxidation stability (<4.0 V vs. Li/Li⁺) is problematic for high-voltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we unveil the crucial effect of ion coordination configuration on oxidation stability by varying the ether backbone structure. The designed 1,3-dimethoxypropane (DMP, C3) forms a unique six-membered chelating complex with Li⁺, whose stronger solvating ability suppresses oxidation side reactions. In addition, the favored hydrogen transfer reaction between C3 and anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7 %) on the cathode surface. As a result, the C3-based electrolyte enables greatly improved cycling of nickel-rich cathodes under 4.7 V. This study offers fundamental insights into rational electrolyte design for developing high-energy-density batteries.     

SPECTROPHOTOMETRIC STUDY OF THE THERMODYNAMICS OF COMPLEXATION OF LITHIUM AND SODIUM IONS WITH DIBENZO-24-CROWN-8 IN BINARY DIMETHYLFORMAMIDE-ACETONITRILE MIXTURES USING MUREXIDE AS A METALLOCHROMIC INDICATOR

Abstract

Complexation of Li⁺ and Na⁺ with dibenzo-24-crown-8 has been studied in dimethylformamide-acetonitrile mixtures by means of a competitive spectrophotometric technique using murexide as metal ion indicator. Stabilities of the resulting 1:1 complexes were investigated at various temperatures and enthalpies and entropies of complexation were determined from the temperature dependence of the formation constants. Sodium forms a more stable complex with the crown ether than lithium. There is an inverse linear relationship between log K_f and the mole fraction of DMF in the solvent mixtures. The ΔH°-TΔS° plot of all thermodynamic data, obtained for both crown complexes in different solvent mixtures, shows a fairly good linear correlation, indicating the existence of an enthalpy-entropy compensation effect in complexation.     

Stabilities in water and transfer activity coefficients from water to nonaqueous solvents of 15-crown-5 and 16-crown-5-metal ion complexes

Stability constants of 1 : 1 16-crown-5 (16C5)-metal ion complexes were determined in water at 25°C by conductometry and potentiometry with ion-selective electrodes. The selectivity sequences of 16C5 in water for univalent and bivalent metal ions are Ag⁺ > Na⁺ Tl⁺ > K⁺ and Sr²⁺ > Ba²⁺ Pb²⁺, respectively. The stability of a given 16C5-metal ion complex in water is much lower than might be expected on the basis of the solvation power (i.e. relative solubility of the metal ion) of water for the metal ion. The same tendency is observed for the cases of 15-crown-5 (15C5) -metal ion complexes. Transfer activity coefficients () of 15C5 and 16C5 for tetradecane (TD)/water, TD/methanol, TD/acetonitrile, and propylene carbonate/water systems were determined at 25°C. From these data, contributions of a methylene group and an ether oxygen atom to the log value of a crown ether were then obtained. The values from water to acetonitrile, propylene carbonate, and methanol of 15C5- and 16C5-univalent metal ion complexes were calculated, s, M⁺, and L being a solvent, a univalent metal ion, and a crown ether, respectively. The log value is greater than the corresponding log value. The log values are negative. This indicates that, although the M^- ions are more soluble in water than in the nonaqueous solvents, when the crown ether forms a complex with the M⁺ ion, the complex becomes more soluble in the nonaqueous solvents than in water, compared with the free crown ether. It was concluded from this finding that the unexpectedly low stability of the crown ether-M⁺ complex in water is attributed to strong hydrogen bonding between ether oxygen atoms of the free crown ether and water.     

Complex formation of O-carboxymethylcalix[4]resorcinolarene with alkaline metal and ammonium ions

Complex formation of 3,5,10,12,17,19,24,26-octa(carboxymethoxy)-1,8,15,22-tetraundecylcalix[4]arene (H₈X) with Li⁺, Na⁺, K⁺, and NH₄ ⁺ ions was studied by ¹H NMR spectroscopy and pH-metry in water—DMSO solutions. Binding of one cation occurs during the stepped deprotonation of four carboxymethyl groups in H₈X. The K⁺ ion was found to be bound more efficiently than Li⁺ and Na⁺. The further deprotonation to the penta- and hexaanion leads to the coordination with two cations. The most stable binuclear complex is formed with the Li⁺ ion.     

Allosteric bindings of thiacalix[4]arene-based receptors with 1,3-alternate conformation having two different side arms

A novel ditopic receptor possessing two complexation sites such as crown ether and 2-pyridylmethyl groups bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with Li⁺ and Ag⁺ have been examined by ¹H NMR titration experiment. The exclusive formation of mononuclear complexes of 1,3-alternate-5 with Li⁺ and Ag⁺ was observed even though the formation of the heterogeneous dinuclear complexes was expected. The decomplexation of Li⁺ from the crown moiety of 1:1 complex 1,3-alternate-5?Li⁺ to form the Ag⁺?1,3-alternate-5 complex by addition of AgSO₃CF₃ clearly shows that pyridyl moiety works as an efficient switch-off of the recognition ability of the crown moiety. We have also developed the construction of hydrogen-bonding self-assembly heterodimeric systems based on bis(4-pyridyl) and dicarboxylic acid thiacalix[4]arene derivatives in 1,3-alternate conformation. Their supramolecular behaviors are studied by ¹H NMR titration experiments with K⁺ and Ag⁺ ions. Although the values of the dimerization constants are relatively small, the stability of the dimers is strong enough to overcome only small conformational changes upon complex formation.     

Spectral deconvolution in electrophoretic NMR to investigate the migration of neutral molecules in electrolytes

Electrophoretic nuclear magnetic resonance (eNMR) is a powerful tool in studies of nonaqueous electrolytes, such as ionic liquids. It delivers electrophoretic mobilities of the ionic constituents and thus sheds light on ion correlations. In applications of liquid electrolytes, uncharged additives are often employed, detectable via ¹H NMR. Characterizing their mobility and coordination to charged entities is desirable; however, it is often hampered by small intensities and ¹H signals overlapping with major constituents of the electrolyte. In this work, we evaluate methods of phase analysis of overlapping resonances to yield electrophoretic mobilities even for minor constituents. We use phase-sensitive spectral deconvolution via a set of Lorentz distributions for the investigation of the migration behavior of additives in two different ionic liquid-based lithium salt electrolytes. For vinylene carbonate as an additive, no field-induced drift is observed; thus, its coordination to the Li⁺ ion does not induce a correlated drift with Li⁺. On the other hand, in a solvate ionic liquid with tetraglyme (G4) as an additive, a correlated migration of tetraglyme with lithium as a complex solvate cation is directly proven by eNMR. The phase evaluation procedure of superimposed resonances thus broadens the applicability of eNMR to application-relevant complex electrolyte mixtures containing neutral additives with superimposed resonances.     

Quantification of the ion transport mechanism in protective polymer coatings on lithium metal anodes

Protective Polymer Coatings (PPCs) have been proposed to protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology. However, the ion transport mechanism in PPCs remains unclear. Specifically, the degree of polymer swelling in the electrolyte and the influence of polymer/solvent/ion interactions are never quantified. Here we use poly(acrylonitrile-co-butadiene) (PAN–PBD) with controlled cross-link densities to quantify how the swelling ratio of the PPC affects conductivity, Li⁺ ion selectivity, activation energy, and rheological properties. The large difference in polarities between PAN (polar) and PBD (non-polar) segments allows the comparison of PPC properties when swollen in carbonate (high polarity) and ether (low polarity) electrolytes, which are the two most common classes of electrolytes. We find that a low swelling ratio of the PPC increases the transference number of Li⁺ ions while decreasing the conductivity. The activation energy only increases when the PPC is swollen in the carbonate electrolyte because of the strong ion–dipole interaction in the PAN phase, which is absent in the non-polar PBD phase. Theoretical models using Hansen solubility parameters and a percolation model have been shown to be effective in predicting the swelling behavior of PPCs in organic solvents and to estimate the conductivity. The trade-off between conductivity and the transference number is the primary challenge for PPCs. Our study provides general guidelines for PPC design, which favors the use of non-polar polymers with low polarity organic electrolytes.

Protective Polymer Coatings (PPCs) protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology.     

Conduction of Li+ cations in ethylene carbonate (EC) and propylene carbonate (PC): comparative studies using density functional theory

Density functional theory is used to study the interaction of Li⁺ cation with ethylene carbonate (EC) and propylene carbonate (PC) comparatively, which are the most popular solvents used in lithium-ion battery composite. In our theoretical calculations, we use DFT hybrid parameter B3LYP5 with a basis set 6–31G** by means of PCGAMESS/Firefly software package. We analyze the optimized structures of EC, PC, and their clusters including lithium-ion. We then calculate solvation energy, desolvation energy, electron affinity, Gibbs free energy, heats of formation of Li⁺ solvated by EC and PC, and the charge on Li⁺. From the above analysis, we observe EC as a better solvent than PC in applications of lithium-ion batteries.     

Stabilities in Polar Nonaqueous Solvents and Transfer Activity Coefficients from Water to Nonaqueous Solvents of 19-Crown-6-Alkali Metal Ion Complexes

Formation constants of 1 : 1 19-crown-6(19C6) complexes with alkali metal ions weredetermined conductometrically at 25 °Cin acetonitrile(AN), propylene carbonate (PC), methanol, DMF, andDMSO. 19C6 always forms the most stable complex withK⁺. The selectivity order of 19C6 forheavy alkali metal ions isK⁺ > Rb⁺ > Cs⁺.The selectivity for Na⁺ varies withthe solvent; that for Li⁺ is the second lowest(AN, DMSO) or the lowest (PC). Transfer activity coefficients(^SH _{2 O}) of19C6 from water to the nonaqueous solvents (S) weremeasured at 25 °C. The contributions of a methylenegroup and an ether oxygen atom to thelog ^SH _{2 O}value of a crown ether wereobtained. The ^SH _{2 O}values of the 19C6–alkali metal ion complexes(^SH _{2 O} (ML⁺)) werecalculated, M⁺ and L denoting an alkali metal ionand a crown ether, respectively. For AN, PC, andCH₃OH, although the M⁺ ion is more stronglysolvated by water than by AN, PC, or CH₃OH, thelog ^SH _{2 O} (ML⁺) islarger than the correspondinglog ^SH _{2 O} (L)expect for the case of M⁺ = Li⁺.The higher lipophilicity of the19C6 complex ion is attributed to an enforcement ofthe hydrogen-bonded structure of water for the complexion caused by the greatly decreased hydrogen bondingbetween ether oxygen atoms and water uponcomplexation. For DMF and DMSO, thelog ^SH _{2 O} (ML⁺) is also greater thanthe correspondinglog ^SH _{2 O} (L).It was concluded from thisfinding that the unexpectedly lowest stability of the19C6 complex ion in water is due to the hydrogenbonding between 19C6 and water. The stabilities and thelog ^SH _{2 O}of 19C6–alkali metal ion complexes were compared with those of 18C6complexes.