Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 degrees C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, "green" chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected. Because it is impossible to experimentally investigate even a small fraction of the potential cation-anion combinations, a molecular-based understanding of their properties is crucial. However, the unusual complexity of their intermolecular interactions renders molecular-based interpretations difficult, and gives rise to many controversies, speculations, and even myths about the properties that ILs allegedly possess. Herein the current knowledge about the molecular foundations of IL behavior is discussed.

Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies

Characterization of a quartz crystal microbalance with simultaneous mass and liquid loading

The nature and properties of surface-enhanced vibrational spectra of molecules adsorbed on surfaces that can enhance the absorption and the emission of electromagnetic radiation are discussed. Examples of surface-enhanced resonant Raman scattering, surface-enhanced Raman scattering in the near-infrared and surface-enhanced infrared are given. The rough surfaces used are metal island films coated with a nanometric organic film using the Langmuir-Blodgett technique or deposited by vacuum evaporation.

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Surface enhanced vibrational spectroscopy

Gas-phase experiments with state-of-the-art techniques of mass spectrometry provide detailed insights into numerous elementary processes. The focus of this Review is on elementary reactions of ions that achieve complete catalytic cycles under thermal conditions. The examples chosen cover aspects of catalysis pertinent to areas as diverse as atmospheric chemistry and surface chemistry. We describe how transfer of oxygen atoms, bond activation, and coupling of fragments can be mediated by atomic or cluster metal ions. In some cases truly unexpected analogies of the idealized gas-phase ion catalysis can be drawn with related chemical transformations in solution or the solid state, and so improve our understanding of the intrinsic operation of a practical catalyst at a strictly molecular level.

Gas-phase catalysis by atomic and cluster metal ions: the ultimate single-site catalysts.

Over the last 2 decades, the quartz crystal microbalance (QCM or QCM-D) has emerged as a versatile tool for investigating soft and solvated interfaces between solid surfaces and bulk liquids becaus...

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Hearing what you cannot see and visualizing what you hear: interpreting quartz crystal microbalance data from solvated interfaces.

Copper ion reduction catalyzed by chloride ions

Chemical reactions of thermalized bare Fe[sub n][sup +] cluster ions (n = 2-13) with ethylene and cyclopropane were studied in a FT-ICR mass spectrometer. The reactivities of Fe[sub n][sup +] cluster ions toward both gases show a pronounced size effect. With ethylene, only Fe[sub 4][sup +] and Fe[sub 5][sup +] react, whereas all the other cluster ions are completely unreactive under the same experimental conditions. In the case of cyclopropane, reactions are observed with Fe[sub 3][sup +], Fe[sub 4][sup +], and Fe[sub 5][sup +]. With both gases, Fe[sub 4][sup +] forms reaction products of stoichiometry Fe[sub 4]C[sub 6]H[sub 6][sup +]. Low-energy collision-induced dissociation (CID) of these reaction products suggests that the carbon and hydrogen atoms on the Fe[sub 4][sup +] nucleus are arranged in such a manner that all 12 atoms are detached simultaneously. Furthermore, comparison with the results from CID experiments on the precursors of the Fe[sub 4]C[sub 6]H[sub 6][sup +] cluster ions reveals that a dramatic bond weakening of the carbon-cluster bonds occurs when the C[sub 6]H[sub 6] stoichiometry is completed on Fe[sub 4][sup +]. This leads to the assumption that benzene is detached. Apparently, Fe[sub 4][sup +] can act as an active center in a catalytic cyclemore » which yields hydrogen and, by CID, benzene from ethylene and from cyclopropane.« less

Evidence for low-pressure catalysis in the gas phase by a naked metal cluster: the growth of benzene precursors on iron (Fe4+)

A quartz oscillator, operated with one of its faces in contact with a liquid, can be used as a highly sensitive microbalance. When use together with an electronic driver circuit, frequency changes will not only reflect changes of vibrating rigid mass but also detect changes of the surface microstructure. Using impedance spectroscopy we have analyzed the influence of the surface microstructure on the frequency changes. A liquid that is rigidly coupled to the surface by inclusion into voids or narrow channels can be discerned from a liquid that is viscously coupled to the surface

Influence of the Surface Microstructure on the Coupling Between a Quartz Oscillator and a Liquid

The charge-transfer reaction between copper(II) and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H 2 SO 4 + 0.3 M CuSO 4 + chloride ions (c C1 ≤ 1 × 10 -2 M), and polyethyleneglycol 1500 (PEG, c PEG ≤ 4 X 10 -3 M). Electrochemical quartz crystal microbalance (EQCM) measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCI on the electrode surface at c C1 ≥ 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCI deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl - surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu + nor Cu ++ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu(II) support the proposed mechanisms, in particular the role of the intermediate Cu + .

http://repositorio.unicamp.br/jspui/bitstream/REPOSIP/102179/1/2-s2.0-0142053149.pdf

An EQCM Study of the Electrochemical Copper(II)/Copper(I)/Copper System in the Presence of PEG and Chloride Ions

We use a vector analyzer to investigate the impedance of a quartz oscillator, one face of which is exposed to a liquid. An aqueous LiCl – solution can be used to vary density and viscosity of the liquid over a wide range. The solution acts as an additional impedance with as well a real as an imaginary part. Furthermore, different electrical driver circuits have been used to excite the crystal vibrations. In most cases, our experimental results deviate from the predicted dependence of the crystal frequency from density and viscosity. These deviations are different for different driving circuits, but they do not change with the properties of the liquid.

Konrad G. Weil

Papers

Copper ion reduction catalyzed by chloride ions

Evidence for low-pressure catalysis in the gas phase by a naked metal cluster: the growth of benzene precursors on iron (Fe4+)

Influence of the Surface Microstructure on the Coupling Between a Quartz Oscillator and a Liquid

An EQCM Study of the Electrochemical Copper(II)/Copper(I)/Copper System in the Presence of PEG and Chloride Ions

Impedance Analysis of Quartz Oscillators, Contacted on One Side with a Liquid