Showing papers on "Ionic bonding published in 2002"

Self-Assembly of Phase-Segregated Liquid Crystal Structures

Abstract: Additional functionality can be incorporated into liquid crystalline materials by using phase segregation and self-assembly. Intermolecular interactions such as hydrogen bonding and ionic interactions play key roles in the formation of these complex structures. One-, two-, and three-dimensional phase-segregated structures on various scales of length are formed by self-assembly of a variety of partially incompatible molecules. Such structures can enhance anisotropic properties such as ionic conductivity.

Ions at the Air/Water Interface

Abstract: We present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and sal...

Green industrial applications of ionic liquids

Abstract: Preface. Obituary: Prof. Murray H. Brooker. Introductory Address. Potential for Use of Ionic Liquids in Czech Industry J. Kotlan. Potential to Apply Ionic Liquids in Industry: Exemplified for the Use as Solvents in Industrial Applications of Homogeneous Catalysis P. Wasserscheid. Ionic Liquids as Catalysts for Ethylbenzene Production M.P. Atkins, C. Bowlas, B. Ellis, F. Hubert, A. Rubatto, P. Wasserscheid. Applications of Ionic Liquids to Biphasic Catalysis H. Olivier-Bourbigou, F. Hugues. High-Temperature NMR Studies of Ionic-Liquid Catalysts O.B. Lapina, V.V. Terskikh, B.S. Bal'zhinimaev, K.M. Eriksen, R. Fehrmann. Ionic Liquids as Alternatives to Traditional Organic and Inorganic Solvents R. Pagni. The Pros and Cons of Using Ionic Liquids in the Pharmaceutical Industry R.M. Freer, A. Curzons. Room Temperature Ionic Liquids as Replacements for Traditional Organic Solvents and their Applications towards 'Green Chemistry' in Separation Processes A.E. Visser, R.P. Swatloski, W.M. Reichert, H.D. Willauer, J.G. Huddleston, R.D. Rogers. Application of Room-Temperature Ionic Liquids to the Chemical Processing of Biomass-Derived Feedstocks L. Moens, N. Khan. Room-Temperature Sulfur Chloride Ionic Liquids in Processes for the Isolation of Noble and Other Metals V.I. Pekhnyo, S.V. Volkov, N.G. Alexandrova. Ionic Liquids for Oil Shale Treatment M. Koel, K. Hollis, J. Rubin, T. Lombardo, B. Smith. Ionic Liquids in the Nuclear Industry: Solutions for the Nuclear Fuel Cycle W.R. Pitner, A.E. Bradley, D.W. Rooney, D. Sanders, K.R. Seddon, R.C. Thied, J.E. Hatter. Non-Invasive Spectroscopic On-Line Methods to Monitor Industrial Processes: A Review M.H. BrookerDAGGER, R.W. Berg. Ionic Liquids as Catalysts for Sulfuric Acid Production and Cleaning ofFlue Gases R. Fehrmann, K.M. Eriksen, S.B. Rasmussen. Modelling the Liquid Behaviour of Ionic Liquids E.A. Gontcharenko, P.F. Zil'berman, V.S. Znamenskii. The Challenges of Building a Molten Salt Database J. Fuller, M. Gaune-Escard. The Past, Present and Future of Ionic Liquids as Battery Electrolytes J. Wilkes. Radical-Ion Melts of Aluminium, Gallium and Sulfur Halides for Novel Power Sources S.V. Volkov, Z.A. Fokina, O.G. Yanko. Electrochemistry of Niobium, Tantalum and Titanium in Low-Temperature Carbamide-Halide Melts N. Tumanova, O. Boyko, N. Buryak, S. Kochetova. Electrochemistry of Niobium in Rubidium and Caesium Halide and Oxohalide Melts, and the Electrochemical Synthesis of Novel Niobium Compounds V.V. Grinevitch, A.V. Arakcheeva, S.A. Kuznetsov. Photochemistry in Ionic Liquids C.M. Gordon. Ionic Liquids Derived from Natural Products and Other Novel Chemistries: Synthesis and Chemistry of Ionic Liquids Composed of Functionalised Ions J.H. Davis, Jr. Ionic Liquids and Supercritical CO2 L.A. Blanchard, Z. Gu, J.F. Brennecke, E.J. Beckman. Acids and Bases in Ionic Liquids K.E. Johnson. Ionic Liquid Crystals as Universal Matrices (Solvents): Main Criteria for Ionic Mesogenicity T.A. Mirnaya, S.V. Volkov. Ionic Liquids as Solvents for Organic Synthesis A.R. Sethi, P. Smith, N. Srinivasan, T. Welton. East-West Collaboration within the NATO Science Programme: Opportunities and Project Management S. Boghosian. Alkane and Cycloalkane Transformations in Superelectrophilic Liquids I.S. Akhrem, A.V. Orlinkov, M.E. Vol'pin. The Dissolution of Kerogen in Ionic Liquids Y. Patell, K.R. Seddon, L. Dutta, A. Fleet. Electrochemical Synthesis of Volatile Metal Complexes, as Precursors for Functional

On the Conductivity Mechanism of Nanocrystalline Ceria

Abstract: Electrical conductivities of Gd-doped (0.15 mol %) and nominally pure nanocrystalline ceramics (~30 nm grain size) were measured by impedance spectroscopy in the temperature range of 673-773 K under various oxygen partial pressures (1- Pa). The ionic and electronic contributions were separated using electrochemical polarization with an electronically blocking electrode, yttria-stabilized zirconia. The results allow for a clear distinction between potential explanations. It is shown that the space charge model (space charge zones with potential of ~0.3 V resulting in depletion of oxygen vacancies and accumulation of conduction electrons) explains all the experimental features. © 2002 The Electrochemical Society. All rights reserved.

CO2 as a separation switch for ionic liquid/organic mixtures

Abstract: A novel technique to separate ionic liquids from organic compounds is introduced which uses carbon dioxide to induce the formation of an ionic liquid-rich phase and an organic-rich liquid phase in mixtures of methanol and 3-butyl-1-methyl-imidazolium hexafluorophosphate ([C4mim][PF6]). If the temperature is above the critical temperature of CO2 then the methanol-rich phase can become completely miscible with the CO2-rich phase, and this new phase is completely ionic liquid-free. Since CO2 is nonpolar, it is not equipped to solvate ions. As the CO2 dissolves in the methanol/[C4mim][PF6] mixture, the solvent power of the CO2-expanded liquid is significantly reduced, inducing the formation of the second liquid phase that is rich in ionic liquid. This presents a new way to recover products from ionic liquid mixtures and purify organic phases that have been contaminated with ionic liquid. Moreover, these results have important implications for reactions done in CO2/ionic liquid biphasic mixtures.

Density functional study of structural and electronic properties of bimetallic silver–gold clusters: Comparison with pure gold and silver clusters

Abstract: Bimetallic silver–gold clusters offer an excellent opportunity to study changes in metallic versus “ionic” properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic AgmAun [3⩽(m+n)⩽5] clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag2Au2, Ag3Au3, and Ag4Au4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag4Au4 and Ag8...

Simple method to determine electronic and ionic components of the conductivity in mixed conductors a review

Abstract: In materials that are of interest for use as solid electrolytes it is important that charge transport is predominantly related to ionic motion, with minimal minority electronic conduction. On the other hand, a number of materials are mixed ionic and electronic conductors. Several DC methods that have been developed over many years to evaluate the separate electronic and ionic components of the total charge transport in solids. These include the Tubandt DC method, the DC assymetric polarization technique sometimes called the Hebb-Wagner method, and the DC open circuit potential method. This paper presents a new method that is relatively simple, and could be advantageous in some cases. It involves the employment and proper interpretation of low amplitude variable frequency AC measurements, a general technique that is often called impedance spectroscopy. As an example, the results of the use of this method on a mixed-conducting perovskite related to the well-known LSGM, La0.4Pr0.4Sr0.2In0.8Mg0.2O2.8, are shown.

Formation, Reactivity, and Properties of Nondative Late Transition Metal–Oxygen and–Nitrogen Bonds

Abstract: Complexes containing bonds between heteroatoms such as nitrogen and oxygen and "late" transition metals (i.e., those located on the right side of the transition series) have been implicated as reactive intermediates in numerous important catalytic systems. Despite this, Our understanding of such M-X linkages still lags behind that of their M-H and M-C analogues. New synthetic strategies have now made possible the isolation and study of a variety of monomeric late-metal alkoxide, aryloxide, and amide complexes, including parent hydroxide and amide species. The heteroatoms in these materials form surprisingly strong bonds to their metal centers, and their bond energies do not necessarily correlate with the energies of the corresponding H-X bonds. The M-X complexes typically exhibit nucleophilic reactivity, in some cases form strong hydrogen bonds to proton donors, and even deprotonate relatively weak acids. These observations, as well as thermodynamic investigations, suggest that late metal - heteroatom bonds are strongly polarized and possess significant ionic character, properties that play an important role in their interactions with organic compounds.

Computer simulation of a green chemistry room-temperature ionic solvent

Abstract: In the interests of making chemistry more environmentally friendly, room-temperature ionic liquids are currently being investigated as alternative solvents in industry and academia. In this paper, we present molecular dynamics simulations of 1-buthyl-3 methylimidazolium hexafluorophosphate ([bmim][PF6]). We compute radial distribution functions, average density, and mean-square displacements for the individual ions. With this information, diffusion coefficients are calculated and conductivities are estimated using the Nernst−Einstein relation. The time history of the mean-square displacement of the ions appears to indicate that the system exhibits complex dynamics with at least two different time scales for diffusion. We model this behavior using a generalized Langevin approach. Results compare well with experimental data reported in the literature.

The Hydrogen Bond in the Solid State

Abstract: The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

Organotellurium compounds as novel initiators for controlled/living radical polymerizations. Synthesis of functionalized polystyrenes and end-group modifications.

Abstract: Polymer-end mimetic organotellurium compounds initiate controlled/living radical polymerization of styrene derivatives that allows accurate molecular weight control with defined end-groups. Transformations of the end-groups via radical and ionic reactions provide a variety of end-group modified polystyrenes.

Aqueous Solution/Air Interfaces Probed with Sum Frequency Generation Spectroscopy.

Abstract: An important issue for developing a molecular-level mechanism of heterogeneous interactions at the aqueous interface is determining changes in the interface with changes in the bulk composition. Development of the nonlinear spectroscopy, sum frequency generation (SFG) provides a technique to probe these changes. Several molecular and ionic solutes have been used to investigate changes in the structure of the aqueous interface. Molecular solutes include glycerol and ammonia. Ionic and associated ion complexes include sulfuric acid as well as alkali sulfate and bisulfate salts. Molecular solutes and associated ion complexes penetrate to the top monolayer of the aqueous-air interface displacing water from the interface. Specifically, the conjectured ammonia−water complex is observed with ammonia tilted, on average, 25−38° from the normal. Ionic solutes generate a double layer in the interfacial region due to the differential distribution of anions and cations near the interface. The strength of the double la...

Influence of ionic inorganic solutes on self-assembly and polymerization processes related to early forms of life: implications for a prebiotic aqueous medium.

Abstract: A commonly accepted view is that life began in a marine environment, which would imply the presence of inorganic ions such as Na+, Cl-, Mg2+, Ca2+, and Fe2+. We have investigated two processes relevant to the origin of life - membrane self-assembly and RNA polymerization - and established that both are adversely affected by ionic solute concentrations much lower than those of contemporary oceans. In particular, monocarboxylic acid vesicles, which are plausible models of primitive membrane systems, are completely disrupted by low concentrations of divalent cations, such as magnesium and calcium, and by high sodium chloride concentrations as well. Similarly, a nonenzymatic, nontemplated polymerization of activated RNA monomers in ice/eutectic phases (in a solution of low initial ionic strength) yields oligomers with >80% of the original monomers incorporated, but polymerization in initially higher ionic strength aqueous solutions is markedly inhibited. These observations suggest that cellular life may not h...

Placement and Characterization of Pairs of Luminescent Molecules in Spatially Separated Regions of Nanostructured Thin Films

Abstract: Methods of making mesostructured sol-gel silicate thin films containing two different molecules deliberately placed in two different spatially separated regions in a one-step, one-pot preparation are developed and demonstrated. When the structure-directing agent is the surfactant cetyltrimethylammonium bromide, the structure is 2-D hexagonal with lattice spacings between 31.6 and 42.1 A depending on the dopant molecules and their concentrations. The three general strategies that are used to place the molecules are philicity (like dissolves like), bonding, and bifunctionality. These strategies take advantage of the different chemical and physical properties of the regions of the films. These regions are the inorganic silicate framework, the hydrophobic organic interior of the micelles, and the ionic interface between them. Luminescent molecules that possess the physical and chemical properties appropriate for the desired strategies are chosen. Lanthanide and ruthenium complexes with condensable trialkoxysilane groups are incorporated into the silicate framework. 1,4-Naphthoquinone, pyrene, rhodamine 6G and coumarin 540A, and lanthanides with no condensable trialkoxysilanes occupy the hydrophobic core of micelles by virtue of their hydrophobicity. The locations of the molecules are determined by luminescence spectroscopy and by luminescence lifetime measurements. In all cases, the long-range order templated into the thin film is verified by X-ray diffraction. The simultaneous placement of two molecules in the structured film and the maintenance of long-range order require a delicate balance among film preparation methodology, design of the molecules to be incorporated in specific regions, and concentrations of all of the species.

Dependence of Ionic Conductivity on Composition of Fast Ionic Conductors Li1+xTi2-xAlx(PO4)3, 0 ≤ x ≤ 0.7. A Parallel NMR and Electric Impedance Study

Abstract: Materials with nominal compositions Li1+xTi2-xAlx(PO4)3, 0 ≤ x ≤ 0.7, have been prepared and studied with X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and electrical impedance techniques. Substitution of Ti4+ by Al3+ reduces the unit cell dimensions of the NASICON framework but enhances the grain interior conductivity. The overall conductivity is dominated by the grain boundary composition. Detection of new broad peaks in the 31P and 27Al MAS NMR spectra supports the formation of an amorphous Li-conducting phase that accounts for the increase observed in the overall conductivity. In samples with x > 0.5, crystallization of Li4P2O7 as a segregated phase is accompanied by the appearance of a new electrical response. In these samples, a decrease in overall conductivity, associated with a modification of the amorphous phase, is also observed.

Use of Organic Esters as Cosolvents in Electrolytes for Lithium-Ion Batteries with Improved Low Temperature Performance

Abstract: The electrolyte composition plays a strong role in determining the low temperature performance of lithium-ion cells, both in terms of ionic mobility in the electrolyte solution, as well as forming suitable surface films on the electrode surfaces A series of ester solvents was chosen for incorporation into multicomponent electrolyte formulations due to their favorable physiochemical properties (i.e., low viscosity, low melting point, and high permittivity), as well as good compatibility with carbonaceous anodes and mixed metal cathodes (i.e LiCoO 2 and LiNiCoO 2 ). In addition to determining the relative facility of lithium intercalation and deintercalation in Li-carbon cells as a function of temperature, a number of conventional electrochemical methods were employed to further enhance the understanding of the nature of the electrode surface films in these ester-based electrolytes, including do polarization and ac impedance measurements A distinct trend was observed with respect to the stability of the surface films formed. In solutions containing low molecular weight cosolvents (i.e., methyl acetate and ethyl acetate) the surface films appear resistive and inadequately protective, whereas electrolytes containing higher molecular weight esters resulted in surface films with more desirable attributes. Promising electrolyte formulations were further evaluated in prototype lithium-ion cells (AA-size) and fully characterized in terms of their low temperature discharge performance.

Discrete stages in the solvation and ionization of hydrogen chloride adsorbed on ice particles

Abstract: Ionization and dissociation reactions play a fundamental role in aqueous chemistry. A basic and well-understood example is the reaction between hydrogen chloride (HCl) and water to form chloride ions (Cl(-)) and hydrated protons (H(3)O(+) or H(5)O(2)(+)). This acid ionization process also occurs in small water clusters and on ice surfaces, and recent attention has focused on the mechanism of this reaction in confined-water media and the extent of solvation needed for it to proceed. In fact, the transformation of HCl adsorbed on ice surfaces from a predominantly molecular form to ionic species during heating from 50 to 140 K has been observed. But the molecular details of this process remain poorly understood. Here we report infrared transmission spectroscopic signatures of distinct stages in the solvation and ionization of HCl adsorbed on ice nanoparticles kept at progressively higher temperatures. By using Monte Carlo and ab initio simulations to interpret the spectra, we are able to identify slightly stretched HCl molecules, strongly stretched molecules on the verge of ionization, contact ion pairs comprising H(3)O(+) and Cl(-), and an ionic surface phase rich in Zundel ions, H(5)O(2)(+).

Synthesis and characterisation of a polyacrylamide-polyacrylic acid copolymer hydrogel for environmental analysis of Cu and Cd

Abstract: A polyacrylamide–polyacrylic acid copolymer hydrogel was prepared by the controlled hydrolysis of polyacrylamide in an alkaline solution of 10% sodium hydroxide. The structure and composition of the resulting copolymer hydrogel was approximately two acrylic acid units for every acrylamide unit. The capacity of the copolymer hydrogel to bind various metal ions was tested under a range of uptake conditions, with varying uptake time, pH and ionic strength. Ions such as Cu 2+ and Cd 2+ were bound more strongly to the copolymer hydrogel than the competing ions of Na + , K + , Ca 2+ and Mg 2+ , particularly at pH>5, largely due to the increased acidity of these transition metal ions. Metals bound to the copolymer hydrogel were efficiently (>94%) eluted in 2 M HNO 3 solution. The copolymer was found to have a p K a of ∼4.5 and had an equilibrium swelling ratio of 120 at pH>6 with an ionic strength equivalent to 0.01 M NaCl, and a swelling ratio of 265 at low ionic strengths. This material should be of use for the recovery and separation of Cu 2+ and Cd 2+ ions, and trace environmental analysis applications such as the diffusive gradients in thin films (DGT) technique.

Purification of gas with liquid ionic compounds

Abstract: The present invention provides a method for purifying a gas by contacting the gas with a liquid ionic compound. Natural gas may be purified, removing water and carbon dioxide, by contacting the natural gas with a liquid ionic compound.

A classification of covalent, ionic, and metallic solids based on the electron density.

Abstract: The electron density of crystals contains all of the information required to complete a classification of their bonding types. We propose here a set of three different indexes, flatness, charge transfer, and molecularity, easily obtained from the experimental or theoretical electron density, which give rise to a classification in close resemblance to the classical van Arkel−Ketelaar diagrams.