Koen Binnemans

A luminescent tris(2-thenoyltrifluoroacetonato)europium(III) complex covalently linked to a 1,10-phenanthroline-functionalised sol–gel glass

Lanthanide doped sol–gel glasses are an attractive type of luminescent material which can be processed at ambient temperatures. However, the solubility of the lanthanide complexes in the sol–gel matrix can be a problem and it is difficult to obtain a uniform distribution of the complexes (avoidance of cluster formation). These problems can be solved by covalently linking the lanthanide complex to the glass matrix. In this study, a strongly luminescent europium β-diketonate complex was immobilized on a 1,10-phenanthroline-functionalised silica sol–gel glass. The glass matrix was prepared by first reacting 5-amino-1,10-phenanthroline with 3-(triethoxysilyl)propyl isocyanate. The resulting compound, tetramethoxysilane (TMOS) and diethoxydimethylsilane (DEDMS) were hydrolysed and condensed at a neutral pH to a sol–gel glass. A tris(2-thenoyltrifluoroacetonato)europium(III) dihydrate complex was bound to the 1,10-phenanthroline groups on the silica gel and the coordinated water was expelled. High-resolution luminescence spectra were recorded and the radiative lifetimes were measured. It is shown that the spectroscopic behaviour of the luminescent materials is very comparable with that of the pure [Ln(tta)3(phen)] complex.

Carboxyl-Functionalized Task-Specific Ionic Liquids for Solubilizing Metal Oxides

Imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium, and quaternary ammonium bis(trifluoromethylsulfonyl)imide salts were functionalized with a carboxyl group. These ionic liquids are useful for the selective dissolution of metal oxides and hydroxides. Although these hydrophobic ionic liquids are immiscible with water at room temperature, several of them form a single phase with water at elevated temperatures. Phase separation occurs upon cooling. This thermomorphic behavior has been investigated by (1)H NMR, and it was found that it can be attributed to the temperature-dependent hydration and hydrogen-bond formation of the ionic liquid components. The crystal structures of four ionic liquids and five metal complexes have been determined.

Immobilization of molecular catalysts in supported ionic liquid phases

In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL) film is immobilized on a high-surface area porous solid and a homogeneous catalyst is dissolved in this supported IL layer, thereby combining the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed. In the first part, general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions. Secondly, organic reactions in which SILP technology is applied to improve the performance of homogeneous transition-metal catalysts are presented: hydroformylation, metathesis reactions, carbonylation, hydrogenation, hydroamination, coupling reactions and asymmetric reactions.

Homogeneous Liquid–Liquid Extraction of Metal Ions with a Functionalized Ionic Liquid

Binary mixtures of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water show an upper critical solution temperature. This solvent system has been used to extract metal ions by phase-transition extraction, using zwitterionic betaine as extractant. The system is efficient for the extraction of trivalent rare-earth, indium and gallium ions. This new type of metal extraction system avoids problems associated with the use of viscous ionic liquids, namely, the difficulty of intense mixing of the aqueous and ionic liquid phases by stirring.

Luminescence of metallomesogens in the liquid crystal state

Recent progress in the design of low-melting liquid-crystalline metal complexes (metallomesogens) has facilitated the study of the photophysical properties of these compounds in the mesophase. Luminescence in the liquid crystal state has been observed for metallomesogens incorporating lanthanide(III), gold(I), silver(I), copper(I) or zinc(II) ions. An alternative approach to liquid-crystalline metal-containing systems is doping a metal complex in a liquid-crystal host. A fascinating property of these materials is the ability to observe linearly polarized emission.

Spectroscopic properties of trivalent lanthanide ions in fluorophosphate glasses

Abstract We describe the spectroscopic properties of the trivalent lanthanide ions Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+ in the fluorophosphate glasses 75NaPO3–24CaF2–1LnF3 and 75NaPO3–20CaF2–5LnF3 (where Ln=lanthanide ion). Absorption and luminescence spectra are discussed. The dipole strengths of the transitions in the absorption spectrum are parametrized in terms of three Ωλ (λ=2, 4 and 6) Judd–Ofelt intensity parameters. These phenomenological parameters are used to predict the luminescence properties of the lanthanide ions in the fluorophosphate glasses. Attention is paid to the trend of the intensity parameters over the lanthanide series.

Temperature dependence of the electrical conductivity of imidazolium ionic liquids

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10(7) Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion.

On the color of the trivalent lanthanide ions

Abstract The energy levels of the trivalent lanthanide ions are rather insensitive to the ligand environment of the central metal ion. Since some of these ions have absorption bands in the visible part of the electromagnetic spectrum, they will show a characteristic color. It is therefore strange that the colors of the trivalent lanthanide ions reported in literature are not always consistent. This Letter reconsiders the problem of the color of the lanthanide ions. Based on the positions of the strongest bands in the absorption spectrum of a trivalent lanthanide ion, the color can be predicted.

An environmentally friendlier approach to hydrometallurgy: highly selective separation of cobalt from nickel by solvent extraction with undiluted phosphonium ionic liquids

A green solvent extraction process for the separation of cobalt from nickel, magnesium and calcium in chloride medium was developed, using undiluted phosphonium-based ionic liquids as extractants. Cobalt was extracted to the ionic liquid phase as the tetrachlorocobaltate(II) complex, leaving behind nickel, magnesium and calcium in the aqueous phase. Manganese is interfering in the separation process. The main advantage of this ionic liquid extraction process is that no organic diluents have to be added to the organic phase, so that the use of volatile organic compounds can be avoided. Separation factors higher than 50 000 were observed for the cobalt/nickel separation from 8 M HCl solution. After extraction, cobalt can easily be stripped using water and the ionic liquid can be reused as extractant, so that a continuous extraction process is possible. Up to 35 g L−1 of cobalt can be extracted to the ionic liquid phase, while still having a distribution coefficient higher than 100. Instead of hydrochloric acid, sodium chloride can be used as a chloride source. The extraction process has been upscaled to batch processes using 250 mL of ionic liquid. Tri(hexyl)tetradecylphosphonium chloride, tri(butyl)tetradecylphosphonium chloride, tetra(octyl)phosphonium bromide, tri(hexyl)tetradecylphosphonium bromide and Aliquat 336 have been tested for their performance to extract cobalt from an aqueous chloride phase to an ionic liquid phase. Tri(hexyl)tetradecylphosphonium chloride (Cyphos IL 101) turned out to be the best option as the ionic liquid phase, compromising between commercial availability, separation characteristics and easiness to handle the ionic liquid.

Pyrrolidinium Ionic Liquid Crystals

N-alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2- thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group C(n)H(2n+1) was varied from eight to twenty carbon atoms (n = 8, 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour purity.