Ion Pairs

An investigation of the interrelationship of cycling performance, solution structure, and electrode surface film structure has been conducted for electrolytes composed of different concentrations of LiPF6 in propylene carbonate (PC) with a binder-free (BF) graphite electrode. Varying the concentration of LiPF6 changes the solution structure, altering the predominant mechanism of electrolyte reduction at the electrode interface. The change in mechanism results in a change in the structure of the solid electrolyte interface (SEI) and the reversible cycling of the cell. At low concentrations of LiPF6 in PC (1.2 M), electrochemical cycling and cyclic voltammetry (CV) of BF graphite electrodes reveal continuous electrolyte reduction and no lithiation/delithiation of the graphite. The solution structure is dominated by solvent-separated ion pairs (Li+(PC)4//PF6–), and the primary reduction product of the electrolyte is lithium propylene dicarbonate (LPDC). At high concentrations of LiPF6 in PC (3.0–3.5 M), electrochemical cycling and CV reveal reversible lithiation/delithiation of the graphite electrode. The solution structure is dominated by contact ion pairs (Li+(PC)3PF6–), and the primary reduction product of the electrolyte is LiF.

The conductance of sodium diethyldithiocarbamate (NaDDC) has been measured in acetonitrile-water mixtures at 25°C where the dielectric constant (D) ranges from 46.52 up to 74.66. Using Fuoss-Onsager theory, the data was interpreted to obtain Λ o , K A and å values. For NaDDC, the ion parameter å (express the solvation) and limiting equivalent conductance Λ o decrease with decreasing the dielectric constant of the medium until it reaches a minimum and then increases again. The increase in log K A versus 1/D plot shows the dominance of electrostatic interaction. By applying the solvent separated – ion pair model, the association constant (K A) is analyzed.

Using the evaporating method, the solubility of sodium chlorate was determined in the various mixed solvents (water + ethanol + propanol) at various temperatures. The results showed that the solubility of NaClO3 decreases with increasing the mass percent of ethanol and propanol. On the other hand, the solubility of NaClO3 increases with increasing the temperature .In addition, the equilibrium constant of ion pair formation, KIP, for the reaction Na + (aq) + ClO3-(aq) Na + ClO3-(Ion Pair) was estimated upon Fuoss contact ion pair model and then, the values of ion-pair concentrations were determined by using the extended Debye-Hückel model and iteration calculations in various mixed solvents and various temperatures. Finally the value of thermodynamic solubility product constant, Ksp(th), and the values of H , S° and G°of ion-pair formation were estimated in the mixed solvent media.

In the present study, two sensitive, precise and accurate spectrophotometric methods have been developed for the determination of milnacipran in bulk and capsule formulation. The first method is based on the reaction of milnacipran with ninhydrin in N,N'-dimethylformamide medium at 80°C temperature to form a colored Ruhemann's purple, which exhibits absorption maximum at 575nm. The second method is based on extraction of milnacipran into chloroform as ion-pair with bromothymol blue. The yellow colored ion-pair complex exhibits absorption maximum at 410nm. Beer’s law is obeyed in the concentration ranges 2.5-37.5μg/mL and 2-12μg/mL of milnacipran for methods I and II, respectively. The effect of experimental variables were investigated and optimized. The validation parameters like linearity, sensitivity, accuracy, precision and robustness were checked by following the ICH guidelines. The proposed methods were applied for the analysis of milnacipran in capsule formulation with good results.

The electronic structure of AgCl–wn (w = H2O and n = 1–6, 8) clusters is investigated by ab initio and time dependent density functional theory calculations with emphasis on the electronic density [ρ(r)] reorganization of the aggregates upon photoexcitation that is characterized by charge migration from the Ag d orbitals and delocalization of ρ(r) around the cation. This is in contrast with NaCl–wn aggregates, where charge migration from Cl− to the water molecules takes place when n >= 5. The results for AgCl–water clusters are also compared with those for photoexcited Cl−–water clusters, which provide a classical illustration of CTTS precursor states.

Small-angle X-ray scattering (SAXS) studies of aqueous [Ta6O19]8−
compared to prior studies of aqueous [Nb6O19]8− reveals key
differences in behaviour, which is likely at the root of the difficultly
in developing polyoxotantalate chemistry. Specifically, where
contact ion-pairing dominates between [Nb6O19]8− and its
counterions, solvent-separated ion-pairing between [Ta6O19]8−
and its counterions has been unveiled in the current study.