Sergio Petrucci

Lithium ion complexation kinetics by cyclic and acyclic polyethers

Results of the ultrasonic absorption relaxation and nuclear magnetic resonance studies of the kinetics of alkali metal cation complexation by macrocycl ic 1 igands in a variety of nonaqueous solvents are reviewed. The effects of a competition between low permittivity solvent molecules, anions, and neutral macrocycles for the first coordination sphere of the lithium cation are clearly evident. utility of the Eigen-Winkler reaction mechanism for describing the ultrasonic absorption results is pointed out. techniques are used to explore the kinetics of lithium ion complexation by acyclic polyethers such as poly(ethy1ene oxide) in acetonitrile a striking insight emerges: The complexation kinetics reflect a localized cation- polyether interaction that is independent of the 1 ength of the polyether chain as one proceeds from triglyme to a poly(ethy1ene oxide) of 15,000 average molar w eight. complexation kinetic studies in neat 1 iquid poly(ethy1ene oxides) is discussed and possible applications of the results in developing an understanding of polymeric electrolytes in 1 ithium batteries is out1 ined. The When the same ultrasonic

Pressure jump relaxation kinetics of the complexation of nickel malonate in D2O

Abstract Pressure jump relaxation kinetic results of the complexation of Ni2+ by malonate ion in deuterium oxide at various temperatures are reported. The data are interpreted by the three step mechanism of Eigen starting from the diffusion controlled approach between the solvated ions and ending with the closing of the chelate ring. The rate determining step is the removal of the first solvent molecule around Ni2+. Comparison of the activation parameters ΔH 23 ∗ and ΔS 23 ∗ , suggests that for both solvents the complexation process has a dissociative mode of activation.

Influence of solvent, anion and presence of nitrogen in the ring structure on the mechanism of complexation of alkali metal cations with crown ethers

The mechanism of complexation of alkali metal cations with macrocyclic ligands such as the simple crown ethers and the role of desolvation vs. ligand rearrangement are discussed. The unique role of water solvent in the rate-determining step of complexations in aqueous solutions is brought into focus. The competitive role of the anion, which becomes of paramount importance in solvents of low permittivity, is reiterated. Monoazo crown ethers are shown to possess isomeric equilibria in methanol solvent. The rate-determining process for the first step of complexation of these macrocycles with Na+ in methanol appears to be the rearrangement of the ligand through inversion to an exo position of the nitrogen lone electron pair. The rate-determining step of the overall complexation is the entrance of the Na+ into the ring with (possibly) concomitant rotation of the lone electron of the nitrogen to an endo configuration.

Microwave dielectric relaxation, electrical conductance and ultrasonic relaxation of LiClO4 in polyethylene oxide dimethyl ether–500 (PEO-500)

The relevance of establishing the structure of electrolyte solutions of low dielectric permittivity is briefly recalled. Microwave complex dielectric permittivities e* = e′ − Je″ in the frequency range ∼1 to 130 GHz for LiClO4 dissolved in poly(ethylene oxide)dimethyl ether of average molar mass 500 (PEO-500), in the concentration range 0.40 to 1 mol dm−3, at 25 °C, are reported. The data are interpreted by a Cole–Davidson distribution function. Molar electrical conductance for the same system, in the concentration range 7 × 10−4 to ∼1 mol dm−3, shows a minimum and a maximum as a function of the electrolyte concentration. The data, in the diluted range (⩽0.017 mol/dm3) are interpreted by the Fuoss–Onsager equation, in terms of free ions and ion-pair-species. Ultrasonic relaxation spectra in the frequency range 1 to 300 MHz and concentration range 0.1 to ∼0.4 mol dm−3, are interpreted by the ion-pair dimerization equilibrium 2LiClO4 ↔ (LiClO4)2, the dimer being an apolar antiparallel species , thus rationalizing the depolarization of the solution with the consequent appearance of a maximum in the dielectric permittivity of the solution at high electrolyte concentration. A parallel with previous work on LiPF6 dissolved in the same solvent is drawn.

Anion solvation effects in polymer-electrolytes: NaSCN and LiSCN in PEO-400 and in PEG-400

Abstract Infrared spectra in the “CN-stretch” region of the SCN − anion, for NaSCN and LiSCN, dissolved in polyethylene oxide dimethylether (PEO-400) of average molar mass 400, show dramatic differences from the infrared spectra of the same electrolytes dissolved in polyethylene oxide glycol (PEG-400) of average molar mass 400. The differences are attributed to anion solvation by the -OH end of the PEG polymers. Similar comparison of the molar refraction R of the two electrolytes dissolved in the two solvents, also shows dramatic differences in the values and concentration dependence of the R NaSCN and of R LiSCN between the two polymer solutions. These differences are also attributed to anion H-bonding solvation by PEG-400. The different molecular status of the above electrolytes in the two solvents, should be considered, when planning their use as ion transport media in polymer-electrolyte batteries.

Molecular relaxation dynamics of poly(propylene oxide glycol)-400–LiClO4 systems

The dynamics of electrolytes dissolved in poly(propylene glycol)s are addressed by a combination of audiofrequency electrical conductivity measurements, IR spectra of the 4 mode of ClO4–, microwave and far-IR dielectric spectra, radiofrequency and UHF ultrasonic absorption spectra, and visible refractivities at the sodium doublet wavelength. The combination of IR and conductivity results indicates that the majority of the electrolyte exists in these low relative permittivity media as a solvent-separated ion pair and not as free ions. The high viscosity of the medium causes an overlap of solvent and solute relaxations that requires a new analysis of the molecular dynamics. The dielectric and ultrasonic spectra correlate with a similar average relexation time but with different distribution parameters. This is ascribed to a similar polymer chain response to the two perturbing functions although with different cooperative character of the response. The dielectric modulus approach is also examined, revealing serious errors committed by the improper use of this method of analysis. The calculated molar refractions suggest that the anion is solvated by the end protons of the polymer chains.

Lithium ion-crown ether complexes in a molten salt

- Lithium ion forms complexes with crown ethers in a basic, room temperature molten salt. The stability constants of several of these complexes have been determined by lithium-7 NMR measurements. The binary molten salt mixture was 55/45 mole % in 1-methyl-3-ethylimidazolium chloride to aluminum(II1) chloride. Stability constants for 1.: 1 complexes with lithium ion were found to increase in the order 18-crown-6 < 12-crown-4 < benzo-15-crown-5 < 15-crcwn5 in this molten salt at 22 OC. This is the same sequence for lithium ion - crown ether complex stability as was found previously in a 55/45 mole % N-butylpyridinium chloride to aluminum(II1) chloride molten salt.

Microwave dielectric relaxation of some liquid ethers

Abstract Complex permittivities, at 25°C, in the frequency range 4-68 GHz, for the liquids 1–3 Dioxolane, dimethoxymethane, 2–2 dimethoxypropane and 1–2 dimethoxyethane are reported. The data for these liquids may be analyzed, within experimental error, by a single Debye relaxation process (up to the investigated frequency of 68 GHz). Correlations between the shear viscosity and the microscopic relaxation time for the above liquids and for methoxy compounds containing rigid aromatic frames have been attempted. It is concluded the major contribution to the observed relaxation times for the liquids investigated containing methoxy groups, is molecular tumbling rather than methoxy group rotation.

Molecular dynamics of macrocycle-metal ion complexes involving heteronuclear binding atoms

Combination of ultrasonic absorption relaxation spectra with infrared absorption spectra yields a clearer picture of the mechanism of complexation of metal ions by macrocycles in nonaqueous solutions. The Eigen-Winkler multistep reaction mechanism has consistently provided a suitable fit of the ultrasonic absorption data for systems such as monovalent sodium cation reacting with 18-crown-6 in acetonitrile. A macrocycle such as Kryptofix 22 having two nitrogen atoms in the ring experiences an exo-exo

Pressure-jump relaxation kinetics in mixed solvents: Ni(NCS)2 in methanol-dimethylsulfoxide and nickel malonate in H2O-d(-) fructose mixtures☆

exo-endo ;ft endo-endo change in conformation readily detected by ultrasonic techniques. Differences in complexation-decomplexation mechanisms deduced from ultrasonic and NMR data can be rationalized in terms of the limitations of the experimental techniques.