Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents

The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.     

Interaction of methanol with amorphous solid water

The interaction of methanol (MeOH) with amorphous solid water (ASW) composed of D2O molecules, prepared at 125 K on a polycrystalline Ag substrate, was studied with metastable-impact-electron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed desorption mass spectroscopy. In connection with the experiments, classical molecular dynamics (MD) simulations have been performed on a single CH3OH molecule adsorbed at the ice surface (T=190 K), providing further insights into the binding and adsorption properties of the molecule at the ice surface. Consistently with the experimental deductions and previous studies, MeOH is found to adsorb with the hydroxyl group pointing toward dangling bonds of the ice surface, the CH3 group being oriented upwards, slightly tilted with respect to the surface normal. It forms the toplayer up to the onset of the simultaneous desorption of D2O and MeOH. At low coverage the adsorption is dominated by the formation of two strong hydrogen bonds as evidenced by the MD results. During the buildup of the first methanol layer on top of an ASW film the MeOH-MeOH interaction via hydrogen-bond formation becomes of importance as well. The interaction of D2O with solid methanol films and the codeposition of MeOH and D2O were also investigated experimentally; these experiments showed that D2O molecules supplied to a solid methanol film become embedded into the film.     

Interaction of NaI with solid water and methanol

The interaction of NaI with amorphous solid water (ASW) and methanol (MeOH) has been investigated with metastable impact electron spectroscopy (MIES), UPS(HeI), and temperature programmed desorption (TPD). We have studied the electron emission from the ionization of the highest-lying states of H(2)O, CH(3)OH, and of 5pI. We have prepared NaI layers on ASW (MeOH) films at about 105 K and annealed them up to about 200 K. Surface segregation of iodide is observed in ASW, as predicted for NaI aqueous solutions. On the other hand, surface segregation is not observed in MeOH, again as predicted for the interaction of NaI with liquid methanol. Electronic properties (ionization potentials, optical band gaps) and water binding energies are reported and are analyzed on the basis of available DFT results for hydrated NaI clusters.     

Electromotive-force studies of mixed electrolytes in mixed solvents. HCl+NH4Cl in methanol+water solvents at 25°C

Electromotive-force measurements of the cell Pt, H₂(g, 1 atm)|HCl(m₁), NH₄Cl(m₂), methanol(X%), Water(100–X)%|AgCl|Ag have been made at 25°C for m₁+m₂=1 mole-kg^–1 and X=0, 10, 20, 30, 40, and 50% methanol by weight. Hydrochloric acid obeys Harned's rule in aqueous solutions, but a quadratic term is required in the mixed solvents. The Harned coefficients for the acid vary with solvent composition, and this invalidates the applicability of Harned's method for estimating activity coefficients for single electrolytes in mixed solvents. This method is described and the reason for the inapplicability of the method is discussed in terms of ion-ion and ion-solvent interactions.     

Enthalpies of transfer from water to methanol of cations complexed with 18-crown-6

Enthalpies of transfer from water to methanol have been obtained via a thermochemical cycle for the [M⁺18C6] complexes where M⁺  Na⁺, K⁺, Rb⁺, Cs⁺, and Ag⁺. Variation of the transfer enthalpy with M⁺ is small.     

Interaction of methanol with ruthenium

The interaction of methanol with a clean (110) ruthenium surface has been studied using temperatures programmed desorption methods. Methanol dissociates upon adsorption at 300 K and yields H₂(g) and chemisorbed CO as the dominant products. Randomization of evolved hydrogen was shown to occur during methanol adsorption and also upon subsequent thermal desorption using isotopically labeled methanol, CH₃OD. In addition to hydrogen and CO, small amounts of H₂CO, CH₃OH, CO₂, and H₂O, are also observed upon thermal desorption. In contrast with a previous study of formaldehyde on Ru(110), no detectable CH₄ product is found upon methanol desorption.     

Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D₂O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111     

Gibbs functions for transfer of divalent metal cations from water to water + methanol mixtures using potentiometry, polarography and solubility measurements

Gibbs functions for transfer from water to methanol and to a full range of water + methanol mixtures were obtained for Cu²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ using potentiometric or polarographic measurements in these solvents. In addition, data were obtained from the solubility products of the alkaline-earth iodates. From values obtained by the different methods and literature data, a table of selected values is given.     

Gas-phase dehydrogenation of methanol with mononuclear vanadium-oxide cations

The reactions of methanol with mass-selected V+, VOH+, VO+, and VO2(+) cations are studied by Fourier-transform ion-cyclotron resonance (FT-ICR) mass spectrometry in order to investigate the influence of the formal oxidation state of the metal on the reactivity of vanadium-oxide compounds. Interestingly, the most reactive species is the low-valent hydroxide cation VOH+, for which a formal condensation reaction prevails to afford VOCH3(+). In contrast, atomic V+ is oxidized and the high-valent dioxide cation VO2(+) is reduced by methanol. The dehydrogenation of methanol mediated by VO+ does not involve any change of the metal's oxidation state. For the latter reaction, the experimental results are complemented by a theoretical investigation by using density functional theory.     

Chelation of Na+ cations in nonaqueous solvents. Structural requirements and methodological considerations

Intrinsic formation constants for complexes of Na⁺ ions with a series of polyamines have been determined from²³Na NMR measurements in binary mixtures of tetrahydrofuran (THF) and amines. The results show in a totally unambiguous manner a regular decrease in the magnitude of the chelate effect with the number of atoms intervening between the nitrogen ligators. The key assumption, tetracoordination of the cation, is critically examined, and experimental evidence is adduced in its support.     

Time-resolved interaction of polar solvents with excited pyrylium cations

The time-resolved fluorescence spectra of two pyrylium-ion derivatives have been investigated. In the temperature range 77 to 190 K, a red-shift of the fluorescence spectra of the order of 25–70 nm is observed and assigned to a fast solvent relaxation process. Time-resolved experiments carried out at 160 K showed a rapid decrease of the emission from the non-relaxed excited state at short wavelengths and a corresponding build-up of the emission of the relaxed one at longer wavelengths. At 120 K emission from the non-relaxed electronic state is predominant.     

Kinetic isotope effect in proton exchange processes between methanol and water in inert solvents

The kinetic isotope effect in proton exchange between methanol and water in CCl₄ solution was studied by¹H and²H NMR and kinetic IR spectroscopy. The exchange rate increases in the series CD₃OH+H₂O3OD+H₂O3OD+D₂O. It has been concluded that the limiting step of the reaction involves the formation of an H-bonded cyclic intermediate.

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¹H ²H - CCl₄. , CD₃OH+H₂O3OD+H₂O3OD+D₂O. , - -.

     

Adsorption of thiourea on mercury in water + methanol mixtures

The adsorption of thiourea on mercury has been investigated by capacitance measurements in three water + methanol mixtures, having various mole fractions of methanol.The back integration method was employed to obtain the curves of surface charge densities at the mercury surface for different concentrations of thiourea in the solution.As a test of specific adsorption in the systems studied the Esin-Markov plots were used.     

UV-visible spectroscopic study of solvation in ternary solvent mixtures: ketocyanine dye in methanol + acetone + water and methanol + acetone + benzene

Solvation characteristics of a ketocyanine dye have been studied in completely miscible ternary solvent mixtures, namely, methanol + acetone + water and methanol + acetone + benzene, by monitoring the solvatochromic absorption band of the dye. The maximum energy of absorption (E) of the solute in a ternary solvent mixture differs significantly from the mole fraction average of the E values in the component solvents. Results in the corresponding binary solvent mixtures also show a deviation of the E value from the mole fraction averaged E values. The results have been explained in terms of preferential solvation using a two phase model of solvation. The excess or deficit over the bulk composition of a solvent component in the vicinity of the solute molecule in a ternary solvent mixture has been estimated using the knowledge of solvation in the corresponding binary mixtures.     

Mechanistic elucidation of the substitution behavior of alkyl cobaloximes in water and methanol as solvents

The ligand substitution behavior of trans-[Co(Hdmg)2(R)S] (R = CH3, PhCH2; Hdmg = dimethylglyoximate; S = H2O and/or MeOH) was studied for imidazole, pyrazole, 1,2,4-triazole, N-acetylimidazole, 5-chloro-1-methylimidazole, NO2-, Ph3P, Ph3As, and Ph3Sb as entering ligands. In all cases, except for Ph3As and Ph3Sb, the observed kinetics shows a linear dependence on the entering nucleophile concentration with no evidence for a back reaction. In the case of Ph3As and Ph3Sb as entering nucleophiles, kinetic evidence for a reverse solvolysis reaction is at hand. Activation parameters (DeltaH++, DeltaS++, and DeltaV++) were determined from the temperature and pressure dependence of all studied reactions and support the operation of a dissociatively activated substitution mechanism. The rate and activation parameters show that there is an increase in the dissociative character from a dissociative interchange to a limiting dissociative mechanism that depends on the nature of R and the entering nucleophile. The crystal structure of trans-[Co(en)2(Me)H2O]2+ was determined by X-ray analysis. The Co-O and Co-C bond lengths were found to be 2.153(6) and 1.995(10) angstroms, respectively. The kinetic and structural data are discussed in reference to a series of earlier studied systems for which data are reported in the literature.     

Interaction of tantalum fluoride with organic solvents

A systematic study on the extraction of tantalum fluoride from various acidic solutions and mixed media has been given using HDEHP, TBP and LA-2 as solvents. The results obtained for these three solvents clarify the ionic behaviour of tantalum. The separation of tantalum from other elements is discussed.