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The structure and stoichiometry of the lanthanide(III) (Ln) complexes with the ligand 2-thenoyltrifluoroacetone (Htta) formed in a biphasic aqueous room-temperature ionic liquid system have been studied by complementary physicochemical methods. Equilibrium thermodynamics, optical absorption and luminescence spectroscopies, high-energy X-ray scattering, EXAFS, and molecular dynamics simulations all support the formation of anionic Nd(tta)4(-) or Eu(tta)4(-) complexes with no water coordinated to the metal center in 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C4mim+Tf2N(-)), rather than the hydrated, neutral complexes, M(tta)(3)(H2O)n)(n = 2 or 3), that form in nonpolar molecular solvents, such as xylene or chloroform. The presence of anionic lanthanide complexes in C4mim+Tf2N(-) is made possible by the exchange of the ionic liquid anions into the aqueous phase for the lanthanide complex. The resulting complexes in the ionic liquid phase should be thought of as weak C4mim+Ln(tta)4(-) ion pairs which exert little influence on the structure of the ionic liquid phase.

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Pulse radiolysis has been used to observe and measure the kinetics for intermolecular positive charge (hole) transfer from biphenyl+ or pyrene+ ions to TMPD molecules in rigid 2-chlorobutane glass at 77 K. These hole transfers occur over distances of about 17 Å at 10−6 s, increasing to about 34 Å at 102 s. The kinetic data are interpreted in terms of current theories which treat electron transfer processes as radiationless transitions. Estimates of the required electron exchange interactions based on the usual electron tunneling models can not explain the fast reactions observed, even when Coulombic effects on the ’’barrier’’ are considered. A superexchange model is proposed which involves interactions propagated by both negative and positive ion states of the solvent. This model adequately interprets the data in terms of a dominant role of the solvent positive ion states, and is also applicable to negative charge transfer in the condensed phase. In samples containing only one solute (biphenyl or pyrene), ion recombination with Cl− removed about one third of the positive ions of the solute between 10−6 and 102 s. The data on intermolecular hole transfer between two solutes must be corrected for the effects of ion recombination. The correction is simple and quantitative only when it is possible to observe decay of the reactants without substantial spectral overlap from the products. Because the effects of ion recombination on product growths are complex, it is not presently possible to use the growths to measure reliably the kinetics intermolecular positive charge transfer.

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Many highly exothermic (2–3 eV) electron transfer reactions are shown to be slower than moderately exothermic reactions by factors as large as 105. The decrease occurs in a regular way with increasing exothermicity, tending to confirm theoretical predictions of Franck–Condon restrictions on strongly exothermic electron transfer reactions. Deviations from the above trends occur if the reaction product, a molecular anion, has a low-lying electronic excited state into which the reaction may occur with more moderate vibrational exothermicity. Then greatly enhanced rates are found. The rates are enhanced to a lesser extent for acceptors likely to undergo configurational changes upon accepting an electron. These effects are found in measurements of rates of electron tunneling reactions between trapped electrons and 48 organic electron acceptors in rigid 2-methyltetrahydrofuran glass at 77 K. Electron tunneling rates were observed from 10−6 to 102 s. Measured tunneling distances were 15–40 Å. In most cases the observed kinetic decay curves are well simulated by a theory in which the only variable parameter is the effective Franck–Condon factor (F), which is a constant characteristic of the acceptor. For the various acceptors F ranges from 1 to 10−5, and scales the reaction rate at each distance. However in reactions of small vibration exothermicity, the Franck–Condon factors are expected to be very sensitive to small changes in reaction exothermicity caused by relaxations of trapped electrons, which deepen their trap depths with time and, possibly, a dispersion of trap depths. These effects cause F to change with time leading to changes in the shapes of the decay curves. The relationship between the shapes of the decay curves, Franck–Condon factors, and exothermicity allows a thorough and consistent semiquantitative interpretation of the present results and much of the earlier tunneling data on electron transfer reactions involving other solvents and solutes.

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The enthalpies for formation of five Eu 3ϩ complexes with N-piperidinomethane-1,1-diphosphonic acid (H 4 pmdp) have been determined by titration calorimetry in 2 M (Na,H)ClO 4 media at 25 ЊC. Both protonation enthalpies and entropies, and the structure of H 4 pmdp in the solid state indicate protonation of the piperidine nitrogen to give a zwitterion in the free ligand. Luminescent lifetime measurements show that the formation of the 1 : 1 and 1 : 2 Eu : L complexes of a variety of methane-1,1-diphosphonic acids liberates an average of 3.3 ± 0.1 water molecules per ligand from the Eu inner hydration sphere. The number of water molecules in the inner coordination sphere and the thermodynamic parameters of the complexes suggest that the structure of the Eu 3ϩ -pmdp complexes and the strength of the Eu 3ϩ -pmdp bonds are similar to those of other methane-1,1-diphosphonic acids despite the presence of the piperidine ring. However, the complexation entropies argue for weaker solvation of the Eu-pmdp complexes probably due to the hydrophobic character of the piperidine ring.