Volume 68, Issue 10

The synthesis and stabilization of metal nanoparticles (M-NPs) from metals, metal salts, metal complexes and metal carbonyls in ionic liquids (ILs) is reviewed. The electrostatic and steric properties of ionic liquids allow for the stabilization of M-NPs without the need of additional stabilizers, surfactants or capping ligands. The synthesis of M-NPs in ILs can be carried out by chemical or electroreduction, thermolysis and photochemical methods including decomposition by microwave or sono-/ultrasound irradiation. Gas-phase syntheses can use sputtering, plasma/glow-discharge electrolysis and physical vapor deposition or electron beam and γ-irradiation. Metal carbonyl precursors M x (CO) y contain the metal atoms already in the zero-valent oxidation state needed for M-NPs so that no extra reducing agent is necessary. Microwave-induced thermal decomposition of precursors in ILs is a rapid and energy-saving access to M-NPs because of the significant absorption efficiency of ILs for microwave energy due to their ionic charge, high polarity and high dielectric constant. M-NP=IL dispersions can be applied in catalytic reactions, e. g., in C-C coupling or hydrogenation catalysis. Graphical Abstract Ionic Liquids for the Synthesis and Stabilization of Metal Nanoparticles

The reaction of antimony(III) chloride with 1,4-dithiane (1,4-dt) in the ionic liquid [BMIM]Cl ([BMIM]Cl: 1-butyl-4-methylimidazolium chloride) with an excess of the Lewis acid AlCl 3 results in the formation of a ligand-stabilized stibenium cation [SbCl 2 ] + . 1,4-Dithiane simultaneously serves as a chelating η2-ligand, exhibiting a boat-like conformation, as well as a bridging μ2-ligand, exhibiting a chair-like conformation, with Sb 3+ as the coordinating cation. Due to the bridging 1,4-dithiane ligands, a chain-like structural building unit 1 ∞ [SbCl 2 (η 2 -1,4-dt) 1/1 (μ 2 -1,4-dt) 2/2 ] + is formed. Graphical Abstract [SbCl 2 (η 2 -1,4-dt)(μ 2 -1,4-dt)][AlCl 4 ]: Ionic Liquid-based Synthesis of a Stibenium Cation (dt = dithiane)

Single crystals of 1-(cyanoethyl)-3-methyl-pyridin-1-ium hexachloridoantimonate(V) (1), 1- (cyanomethyl)-3-methyl-pyridin-1-ium hexachloridoniobate(V) (2), 1-(cyanomethyl)-3-methylpyridin- 1-ium hexachloridotantalate(V) (3), 1-(cyanopropyl)-3-methyl-pyridin-1-ium hexachloridoniobate( V) (4), and 1-(cyanopropyl)-3-methyl-pyridin-1-ium hexachloridotantalate(V) (5) have been synthesized and characterized by X-ray diffraction. Compounds 1-3 crystallize in the triclinic space group P1̄ with Z = 2, and compounds 4 and 5 in the monoclinic space group C2/c with Z = 8. FTRaman spectra have been recorded and interpreted, especially with respect to the anions [MCl 6 ] - . In addition, NMR spectra, a study of the melting behavior and elemental analyses complete the characterization. Graphical Abstract Ionic Liquids Based on Hexachloridometalate(V) Anions (Sb, Nb and Ta) and Nitrile-functionalized Pyridinium Cations

[HMIM][Br 9 ] ([HMIM]=1-hexyl-3-methylimidazolium) has been investigated by Raman spectroscopy, single-crystal X-ray diffraction and NMR spectroscopy. Conductivity measurements show a high electrical conductivity like other polybromides. Graphical Abstract [HMIM][Br 9 ]: a Room-temperature Ionic Liquid Based on a Polybromide Anion

The high-temperature syntheses of the low-valent halogenides P 2 I 4 , Te 2 Br, a-Te 4 I 4 , Te 4 (Al 2 Cl 7 ) 2 , Te 4 (Bi 6 Cl 20 ), Te 8 (Bi 4 Cl 14 ), Bi 8 (AlCl 4 ) 2 , Bi 6 Cl 7 , and Bi 6 Br 7 , as well as of WSCl 4 and WOCl 4 have been replaced by resource-efficient low-temperature syntheses in room temperature ionic liquids (RTILs). The simple one-pot syntheses generally do not require elaborate equipment such as two zone furnaces or evacuated silica ampoules. Compared to the published conventional approaches, reduction of reaction time (up to 80%) and temperature (up to 500 K) and, simultaneously, an increase in yield were achieved. In the majority of cases, the solid products were phase-pure. X-Ray diffraction on single crystals (redetermination of 11 crystal structures) has demonstrated that the quality of the crystals from RTILs is comparable to that of products obtained by chemical transport reactions. Graphical Abstract Substitution of Conventional High-temperature Syntheses of Inorganic Compounds by Near-room-temperature Syntheses in Ionic Liquids

We have synthesized twelve new ionic liquids composed of an imidazolium-based cation in combination with an anion that shows antiobiotic or analgesic activity. These “BIOnic Liquids” have been tested towards their antibiotic activity in a standardized microbiological assay. A surprizingly large number of compounds shows high activity towards a set of bacteria which cannot be explained as simple cumulative effects. The general concept opens up completely new possibilities for the future development of pharmaceutically active compounds. Graphical Abstract BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity

We present the application of ionic liquid-aqueous micellar solutions as isolation media for the pharmaceutically active ingredient piperine from black pepper. Several surface-active ionic liquids including a biodegradable betaine derivative were used for the extraction of piperine, and a strong correlation between extraction yield and the critical micelle concentration of the respective ionic liquid was found. A scaled strategy for the isolation of piperine was developed that allowed recovery and recycling of the aqueous ionic liquid micellar solution for five runs without any loss in extraction efficiency. Graphical Abstract Surface-active Ionic Liquids for Micellar Extraction of Piperine from Black Pepper

Polyoxomolybdates were generated in situ by treating a carboxylic acid-functionalized ionic liquid with an aqueous solution of sodium molybdate. This reaction mixture was applied in the catalytic epoxidation of olefins using hydrogen peroxide as oxidant. The influence of acid and catalyst concentration as well as of the reaction temperature was investigated. The system showed a good performance for the epoxidation reaction and can be reused several times without a significant loss of activity. We present an easy, cheap and environmentally friendly catalytic system for the epoxidation of cis-cyclooctene. Graphical Abstract Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in-situ in Ionic Liquids

Results of potential-dependent differential capacitance measurements on the interface between six different ionic liquids and the (111) surface of single-crystalline gold are presented. The measurements were done by means of broadband impedance spectroscopy in a frequency range from 10 mHz to 1 MHz. We discuss the influence of the IL cation, the IL anion and the cations’ alkyl chain length on the interfacial capacitance. Our results suggest that (i) there is no simple relationship between the cation size and the value of the differential capacitance, (ii) the general shape of the potentialdependent differential capacitance curve is more strongly influenced by the IL anion, and (iii) experimental differential capacitance curves do not exhibit a simple “camel-” or “bell-shaped” curvature as predicted by mean-field theories. Furthermore, the broadband measurements show that two capacitive processes can be distinguished, which take place on millisecond and second time scales, respectively. While a millisecond time scale is expected for double-layer charging governed by the bulk conductivity of the IL, the existence of a slow process points to additional barriers for charge transport at the interface. The capacitance contribution of the slow process is most pronounced for ILs based on the N-butyl-N-methyl-pyrrolidinium ([Pyr 1,4 ]) cation. A comparison of capacitance data with insitu STM data from previous studies suggests that the slow process is connected to herringbone-type structures at the interface. While the herringbone superstructure of the Au(111) surface is well known in aqueous electrochemistry, a herringbone-type structure of adsorbed ions was described in a recent MD simulation paper by Federov and coworkers (K. Kirchner, T. Kirchner, V. Ivaništĕv, M. V. Fedorov, Electrochim. Acta 2013, in press: doi: 10.1016/j.electacta.2013.05.049). Graphical Abstract The Differential Capacitance of Ionic Liquid / Metal Electrode Interfaces – A Critical Comparison of Experimental Results with Theoretical Predictions

Six 1-alkyl-4-tridecafluorooctyl-1,2,4-triazolium triflimides 2a-f and 4-amino-1-tridecafluorooctyl- 1,2,4-triazolium triflimide (4) were prepared from the respective iodides 1a-f (1a, 2a: n-propyl; 1b, 2b: n-butyl; 1c, 2c: n-hexyl; 1d, 2d: n-heptyl; 1e, 2e: n-octyl; 1f, 2f: n-decyl) and iodide 3 by ion metathesis. Compounds 2a and 4 are liquid at room temperature. Two liquid fluorous imidazolium salts bearing functionalized polar substituents were synthesized in an analogous manner, namely 1-(2- (diethylamino)ethyl)-3-(heptadecafluorodecyl)imidazolium triflimide (5b) and 1-(2-hydroxyethyl)- 3-(heptadecafluorodecyl)imidazolium triflimide (6b) from the respective bromides 5a and 6a. The bis(triflimide) 5c has a melting point slightly above room temperature. Three fluorous ionic liquids (ILs; 2a, 5b, and 6b) were subjected to vapor sorption analysis at 25 °C and exhibited dual affinity to water and, even much more pronounced, to methoxynonafluorobutane (hydrofluoroether HFE-7100). Thus, IL 6b absorbed 3:2% (by weight) water and 200% HFE, whereas ILs 2a and 5b absorbed 0.4 and 0:5% water, but 300 and 1200% HFE, respectively. Commercial 1-butyl-2,3- dimethyl-imidazolium triflimide and 1-ethyl-3-methyl-imidazolium triflimide were used as reference compounds and absorbed 0.9 and 2:2% water, respectively, but only 17% HFE. Graphical Abstract Synthesis and Sorption Analysis of Task-specific Fluorous Ionic Liquids

Ionogel fiber mats were made by electrospinning poly(methylmethacrylate) (PMMA) and the ionic liquid (IL) bis(1-butyl-3-methyl-imidazolium) tetrachloridocuprate(II), [Bmim] 2 [CuCl 4 ], from acetone. The morphology of the electrospun ionogels strongly depends on the spinning parameters. Dense and uniform fiber mats were only obtained at concentrations of 60 to 70 g L -1 of polymer and IL mass combined. Lower concentrations led to a low number of poorly defined fibers. High voltages of 20 to 25 kV led to well-defined and uniform fibers; voltages between 15 and 20 kV again led to less uniform and less dense fibers. At 10 kV and lower, no spinning could be induced. Finally, PMMA fibers electrospun without IL show a less well-defined morphology combining fibers and oblong droplets indicating that the IL has a beneficial effect on the electrospinning process. The resulting materials are prototypes for new functional materials, for example in sterile filtration. Graphical Abstract Ionogel Fiber Mats: Functional Materials via Electrospinning of PMMA and the Ionic Liquid Bis(1-butyl-3-methyl-imidazolium) Tetrachloridocuprate(II), [Bmim] 2 [CuCl 4 ]