A structural and electrochemical investigation of 1-alkyl-3-methylimidazollum salts of the nitratodioxouranate(VI) anions [{UO2(NO3)(2)}(2)(mu(4)-C2O4)](2-), [UO2(NO3)(3)](-), and [UO2(NO3)(4)](2-)

The properties of the 1-butyl-3-methylimidazolium salt of the dinuclear mu(4)-(O,O,O',O'-ethane-1,2-dioato)bis[bis-(nitrato-O,O)dioxouranate(VI)] anion have been investigated using electrochemistry, single-crystal X-ray crystallography, and extended X-ray absorbance fine structure spectroscopy: the anion structures from these last two techniques are in excellent agreement with each other. Electrochemical reduction of the complex leads to the a two-electron metal-centered reduction of U(VI) to U(IV), and the production Of UO2, or a complex containing UO2. Under normal conditions, this leads to the coating of the electrode with a passivating film. The presence of volatile organic compounds in the ionic liquids 1-alkyl-3-methylimidazolium nitrate (where the 1-alkyl chain was methyl, ethyl, propyl, butyl, pentyl, hexyl, dodecyl, hexadecyl, or octadecyl) during the oxidative dissolution of uranium(IV) oxide led to the formation of a yellow precipitate. To understand the effect of the cation upon the composition and structure of the precipitates, 1-alkyl-3-methylimidazolium salts of a number of nitratodioxouranate(VI) complexes were synthesized and then analyzed using X-ray crystallography. It was demonstrated that the length of the 1-alkyl chain played an important role, not only in the composition of the complex salt, but also in the synthesis of dinuclear anions containing the bridging mu(4)-(O,O,O',O'-ethane-1,2-dioato), or oxalato, ligand, by protecting it from further oxidation.

Alkali-metal salts of aromatic carboxylic acids: Liquid crystals without flexible chains

The alkali-metal salts of meta-substituted benzoic acids exhibit a smectic A mesophase at high temperatures. These compounds are examples of liquid crystals without terminal alkyl chains. The influence of the metal ion and of the type of substituents on the transition temperatures is discussed. Compounds with the substituent in the ortho- and para-positions are non-mesomorphic. The crystal structures of the compounds Rb(C7H4ClO2)(C7H4ClO2H), Na(C7H4IO2)(H2O), K(C7H4ClO2)(C7H4ClO2H) and Rb(C7H4BrO2)(C7H4BrO2H) have been determined by X-ray crystallography. These compounds possess a layerlike structure in the solid state. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Lead(II) chloride ionic liquids and organic/inorganic hybrid materials - a study of chloroplumbate(II) speciation

A range of chloroplumbate(II) organic salts, based on the two cations, 1-ethyl-3-methylimidazolium and trihexyl(tetradecyl) phosphonium, was prepared by ionothermal synthesis. Depending on the structure of the organic cation and on the molar ratio of PbCl2 in the product,.PbCl2, the salts were room-temperature ionic liquids or crystalline organic/inorganic hybrid materials. The solids were studied using Raman spectroscopy; the crystal structure of [C(2)mim]{PbCl3} was determined and shown to contain 1D infinite chloroplumbate(II) strands formed by edge-sharing tetragonal pyramids of pentacoordinate (PbCl5) units. The liquids were analysed using Pb-207 NMR and Raman spectroscopies, as well as viscometry. Phase diagrams were constructed based on differential scanning calorimetry (DSC) measurements. Discrete anions: [PbCl4](2-) and [PbCl3](-), were detected in the liquid state. The trichloroplumbate(II) anion was shown to have a flexible structure due to the presence of a stereochemically-active lone pair. The relationship between the liquid phase anionic speciation and the structure of the corresponding crystalline products of ionothermal syntheses was discussed, and the data were compared with analogous tin(II) systems.

Local and semilocal density functional computations for crystals of 1-alkyl-3-methyl-imidazolium salts

The accuracy and reliability of popular density functional approximations for the compounds giving origin to room temperature ionic liquids have been assessed by computing the T=0 K crystal structure of several 1-alkyl-3-methyl-imidazolium salts. Two prototypical exchange-correlation approximations have been considered, i.e., the local density approximation (LDA) and one gradient corrected scheme [PBE-GGA, Phys. Rev. Lett. 77, 3865 (1996)]. Comparison with low-temperature x-ray diffraction data shows that the equilibrium volume predicted by either approximations is affected by large errors, nearly equal in magnitude (~10%), and of opposite sign. In both cases the error can be traced to a poor description of the intermolecular interactions, while the intramolecular structure is fairly well reproduced by LDA and PBE-GGA. The PBE-GGA optimization of atomic positions within the experimental unit cell provides results in good agreement with the x-ray structure. The correct system volume can also be restored by supplementing PBE-GGA with empirical dispersion terms reproducing the r-6 attractive tail of the van der Waals interactions.

Effect of reduced pH on inorganic polyphosphate accumulation by Burkholderia cepacia complex isolates.

Aims: Burkholderia cepacia complex (Bcc) isolates causing pulmonary infection in cystic fibrosis (CF) patients grow within an acidic environment in the lung. As exposure to acid pH has been shown to increase intracellular inorganic polyphosphate (polyP) formation in some bacteria, we investigated the inter-relationship between acidic pH and polyP accumulation in Bcc isolates.

Clusters, liquids and crystals of dialkylimidazolium salts. A combined perspective from ab initio computer simulations

We summarize results obtained by a combination of ab initio and classical computer simulations of dialkylimidazolium ionic liquids in different states of aggregation, from crystals to liquids and clusters. Unusual features arising from the competition between electrostatic, dispersion, and hydrogen-bonding interactions are identified at the origin of observed structural patterns. We also discuss the way Brønsted acids interact with ionic liquids leading to the formation of hydrogen-bonded anions.

Electrooxidation of the iodides [C(4)mim]I, LiI, NaI, KI, RbI, and CsI in the room temperature ionic liquid [C(4)mim][NTf2]

The electrochemical oxidation of 1-butyl-3-methylimidazolium iodide, [C(4)mim]I, has been investigated by cyclic voltammetry at a platinum microelectrode at varying concentrations in the RTIL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(4)mim][NTf2]. Two oxidation peaks were observed. The first peak is assigned to the oxidation of iodide to triiodide, in an overall two-electron process: 3I(-)- 2e(-) -> I-3(-). At higher potentials, the electrogenerated triiodide oxidizes to iodine, in an overall one-electron process: I-3(-) - e(-) -> 3/2I(2). An average diffusion coefficient, D, for I- of 1.55 x 10(-11) m(2) s(-1) was obtained. A digital simulation program was used to simulate the voltammetric response, and kinetic parameters were successfully extracted. The parameters deduced from the simulation include D for I-, I-3(-), and I-2 and K-eq,K-2, the equilibrium constant for the reaction of iodide and iodine to form triiodide. Values for these parameters are of the same order as those previously published for the oxidation of Br- in the same RTIL [Allen et al. J. Electroanal. Chem. 2005, 575, 311]. Next, the cyclic voltammetry of five different inorganic iodide salts was studied by dissolving small amounts of the solid in [C(4)mim][NTf2]. Similar oxidation peaks were observed, revealing diffusion coefficients of ca. 0.55, 1.14, 1.23, 1.44, and 1.33 x 10(-11) m(2) s(-1) and solubilities of 714, 246, 54, 83, and 36 mM for LiI, NaI, KI, RbI, and CsI, respectively. The slightly smaller diffusion coefficients for the XI salts (compared to [C(4)mim]I) may indicate that I- is ion-paired with Li+, Na+, K+, Rb+, and Cs+ in the RTIL medium.

Application of EXAFS to molten salts and ionic liquid technology

This paper describes the use of extended X-ray absorption fine structure spectroscopy (EXAFS) to examine the structure of molten salts and ionic liquids and species dissolved in them. The EXAFS theory is briefly described as are the methods by which EXAFS of these systems can be studied. A range of applications have used EXAFS to investigate the structure of metallic species in ionic liquids from extraction studies to catalysts. The area of structural investigations of ionic liquids is still being developed, although growing rapidly, whereas the structure of molten salts has been studied using EXAFS in more detail.