N-donor ligands based on bipyridine and ionic liquids: an efficient partnership to stabilize rhodium colloids. Focus on oxygen-containing compounds hydrogenation

Polynitrogen ligands and/in ionic liquids (ILs) are described as a pertinent tandem to efficiently stabilize rhodium nanoparticles (NPs) in the size range of 2.0 nm for catalytic applications. Several N-donor ligands based on bipyridine skeleton were used as extra protective agents in [BMI][PF(6)] and compared in the hydrogenation of functionalized aromatic compounds at 80 °C and under 40 bar H(2). The nature of the bipyridine derivative and its influence on the coordination mode on the particle surface were proposed to explain the observed different kinetic properties. The hydrogenation of various oxygen-containing arenes was investigated and original results were described in the reduction of anisole and cresols as model lignin compounds, providing a significant ratio of ketone derivatives. A first explanation based on possible reaction routes is proposed to justify the formed products.     

Spontaneous formation and electrogenerated chemiluminescence of tris(bipyridine) Ru(II) derivative nanobelts

The single crystalline nanobelts were successfully fabricated with an ionic compound by a simple reprecipitation method. The compound used is the water-insoluble derivative of tris(bipyridine) Ru(II), [Ru(bpy)2(4,4'-(CH3(CH2)14COO)2-bpy)](ClO4)2. The prepared nanobelts show an enhanced fluorescence emission and relatively strong electrogenerated chemiluminescence (ECL), that have potential analytical applications. More interesting, ECL of a single nanobelt deposited on an ultramicroelectrode was observed. The observation of ECL in such nanostructures leads to the development of a new class of ECL systems that may prove useful for a variety of purposes.     

Enhanced rate of arene hydrogenation with imidazolium functionalized bipyridine stabilized rhodium nanoparticle catalysts

The imidazolium functionalized bipyridine compounds, {4,4'-bis[7-(2,3-dimethylimidazolium)heptyl]-2,2'-bipyridine}(2+) ([BIHB](2+)) and {4,4'-bis[(1,2-dimethylimidazolium)methyl]-2,2'-bipyridine}(2+) ([BIMB](2+)), were prepared and used as Rh nanoparticle stabilizers. The dispersed Rh nanoparticles were used as catalysts in the biphasic hydrogenation of various arene substrates. The catalytic activity was strongly influenced by the stabilizer employed and followed the trend [BIHB](2+) > bipy > [BIMB](2+). The steric and electronic characteristics of the imidazolium functionalized bipyridine ligands were assessed via the synthesis of rhenium carbonyl complexes, which facilitated the rationalization of the catalytic properties of the nanoparticles.     

Odd-even effect and metal induced structural convergence in self-assembled monolayers of bipyridine derivatives

Scanning tunneling microscopy (STM) observations reveal that bipyridine derivatives which exhibit various two-dimensional structures due to the odd-even chain length effect are converged into a lamellar structure upon metal coordination.     

Air and water stable ionic liquids in physical chemistry

Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 degrees C or below. Originating from electrochemistry in AlCl(3) based liquids an enormous progress was made during the recent 10 years to synthesize ionic liquids that can be handled under ambient conditions, and today about 300 ionic liquids are already commercially available. Whereas the main interest is still focussed on organic and technical chemistry, various aspects of physical chemistry in ionic liquids are discussed now in literature. In this review article we give a short overview on physicochemical aspects of ionic liquids, such as physical properties of ionic liquids, nanoparticles, nanotubes, batteries, spectroscopy, thermodynamics and catalysis of/in ionic liquids. The focus is set on air and water stable ionic liquids as they will presumably dominate various fields of chemistry in future.     

Synthesis and crystal structures of mononuclear iridium (III) acetylacetonate complexes bearing an axial bipyridine ligand

Three new iridium (III) acetylacetonate complexes with an axial bipyridine ligand were synthesised via the direct reaction of [bis(acac-O,O′)(acac-C³)Ir(H₂O)] and the corresponding bipyridine, and their molecular structures were determined by using single-crystal X-ray diffraction. The bipyridine used was di-2-pyridylketone, 2,2′-bipyridine and 2,2′-bipyridylamine, respectively. The results revealed that only mononuclear iridium complexes were obtained, although bipyridine has two N coordinate atoms, probably due to the great steric hindrance existing around the coordinate sphere if two bis(acac-O,O′)(acac-C³)Ir units were bridged by bipyridine. All these complexes are coordinated in one axial direction by bipyridine as a mono-dentate ligand in a slightly distorted octahedral coordination geometry.     

Allosteric effects in a ditopic ligand containing bipyridine and tetra-aza-crown donor units

Artificial allosterism: A ditopic ligand, which contains both bipyridine and tetra-aza-crown binding sites, coordinates one Cu(II) through all four N-donors of the tetradentate aza-crown unit. Reaction at the bipyridine site with another Cu(II) allosterically changes the aza-crown from being a tetradentate to a tridentate N-donor unit, a change in coordination mode that causes the successive binding of two Cu(II) ions to proceed with severe negative cooperativity (see scheme).     

Preparation of ionic liquid/silica nanocomposites possessing no weight loss characteristic after calcination at 800 °C

Tetraethoxysilane reacted with silica nanoparticles in the presence of a variety of ionic liquids such as phosphonium-, ammonium-, and imidazolium-type ionic liquids under alkaline conditions to afford the corresponding ionic liquid/silica nanocomposites with a good dispersibility and stability in numerous solvents. It was demonstrated that these ionic liquid nanocomposites can be classified into the nanocomposites possessing no weight loss and weight loss characteristics after calcination at 800 °C, respectively, according to the ionic liquid structures in the composites. The ionic liquids except for 1-ethyl-3-methylimidazolium hydrogen sulfate were found to afford the corresponding ionic liquid/silica nanocomposites possessing no weight loss characteristic even after calcination at 800 °C.

Synthesis and characterization of catalytic iridium nanoparticles in imidazolium ionic liquids

The reduction of [Ir(cod)Cl](2) (cod=1,5-cyclooctadiene) dissolved in 1-n-butyl-3-methyl tetrafluoroborate, hexafluorophosphate and trifluoromethane sulphonate ionic liquids in the presence of 1-decene by molecular hydrogen produces Ir(0) nanoparticles. The formation of these nanoparticles follows the two-step [A-->B, A+B-->2B (k(1),k(2))] autocatalytic mechanism. The same mean diameter values of around 2-3 nm were estimated from in situ TEM and SAXS analyses of the Ir(0) nanoparticles dispersed in the ionic liquids and by XRD of the isolated material. XPS and EXAFS analyses clearly show the interactions of the ionic liquid with the metal surface demonstrating the formation of an ionic liquid protective layer surrounding the iridium nanoparticles. SAXS analysis indicated the formation of an ionic liquid layer surrounding the metal particles with an extended molecular length of around 2.8-4.0 nm depending on the type of the anion.     

Magnetic Nanoparticles Supported Ionic Liquids Improve Firefly Luciferase Properties

Ionic liquids as neoteric solvents, microwave irradiation, and alternative energy source are becoming as a solvent for many enzymatic reactions. We recently showed that the incubation of firefly luciferase from Photinus pyralis with various ionic liquids increased the activity and stability of luciferase. Magnetic nanoparticles supported ionic liquids have been obtained by covalent bonding of ionic liquids-silane on magnetic silica nanoparticles. In the present study, the effects of [γ-Fe₂O₃@SiO₂][BMImCl] and [γ-Fe₂O₃@SiO₂][BMImI] were investigated on the structural properties and function of luciferase using circular dichroism, fluorescence spectroscopy, and bioluminescence assay. Enzyme activity and structural stability increased in the presence of magnetic nanoparticles supported ionic liquids. Furthermore, the effect of ingredients which were used was not considerable on K _m value of luciferase for adenosine-5′-triphosphate and also K _m value for luciferin.     

Tunable wettability of polyimide films based on electrostatic self-assembly of ionic liquids

We have demonstrated that the surface wettability of negatively charged polyimide films could be tuned by electrostatic self-assembly of ionic liquids. The water contact angles of the polyimide films varied in the range 27-80 degrees for 13 different ionic liquids based on imidazolium and ammonium salts. The surface morphology of the resulting surfaces was characterized using atomic force microscopy. The results revealed that the assembly of longer-substituent cations was characterized by the formation of spherical nanoparticles that were formed due to sequent aggregation of cations on those electrostatically assembled ones via hydrophobic interaction. In this case, the counteranions are present in the assembled layers and the wettability is accordingly affected. Whereas for shorter-substituent cations, no aggregates were formed due to the less hydrophobic interaction than the electrostatic repulsive interaction between the cations, and the counteranions were absent from the assembled layers. This method can also be utilized to quantify the hydrophobicity of various ionic liquids.     

Stability of sputter-deposited gold nanoparticles in imidazolium ionic liquids

The stability of gold nanoparticles synthesised by sputter deposition has been studied in situ in 1-butyl-3-methylimidazolium ionic liquids with bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate and dicyanamide anions with UV-VIS absorption spectroscopy and transmission electron microscopy. Besides the growth of the gold nanoparticles, two other processes were observed after sputtering, namely aggregation and sedimentation of these nanoparticles. To model the absorption spectra of the sputtered gold nanoparticles, generalized multiparticle Mie calculations were performed. These theoretical calculations confirm the increase in absorbance at longer wavelength for larger aggregates and are in agreement with the experimental observations. It was found that the kinetics of aggregation and sedimentation scale with the viscosity of the ionic liquid. Small amounts of water were found to have a large detrimental influence on the stability of the colloidal suspensions of the gold nanoparticles in ionic liquids. From the large discrepancy between the theoretical and the experimentally observed stability of the NPs, it was concluded that structural forces stabilize the gold nanoparticles. This was also borne out by AFM measurements.     

Plasma electrochemistry in ionic liquids: an alternative route to generate nanoparticles

In this perspective, the application of stable glow discharge plasmas as free electrodes for the generation of nanoparticles in ionic liquids is reported. The basic concepts of plasma electrochemistry as well as a few other concepts in this field will be presented. One focus is the interaction of the plasma with the ionic liquids itself and possible influences on the production process of the particles. Several examples of the plasma generation and characterisation of nanoparticles in ionic liquids will be presented. The starting point is thereby the generation of noble metals and at the end the efforts to synthesize semiconductor nanoparticles will be discussed. In all examples the benefits, the difficulties and the challenges of this method and the outcome for the future will be addressed.     

Hydroamination of phenylacetylene in the presence of gold-containing catalytic systems supported on carriers modified by ionic liquids

Ternary systems based on gold nanoparticles stabilized in ionic liquids and loaded on the supports of various nature have been prepared for the first time. The gold-containing systems obtained demonstrate activity in Markovnikov regioselective hydroamination of phenylacetylene with aniline. Catalytic properties of the gold systems synthesized depend both on the carrier structure and on the nature of the ionic liquid applied (polarity, presence of functional groups).     

Metal sols in ionic liquids: synthesis,properties, and application

This review contains the analysis of the state-of-the-art data on synthesis, structure, and practical application of metal sols in ionic liquids. Problems related to stabilization of metallic nanoparticles by the components of ionic liquids are analyzed in detail. Information on catalytic properties of metal sols in ionic liquids is generalized. Examples illustrating practical application of these systems in diverse areas of science and technology are presented.

     

Paramagnetic surface active ionic liquids: synthesis,properties, and applications

Paramagnetic surface active ionic liquids (PMSAILs) classify task-specific ionic liquids with magnetic properties by incorporating metal into the cationic or anionic part of the ionic liquid. Paramagnetic ionic liquids had long-chain either in cations or anions and showed excellent surface activity and magnetic properties without any need for the magnetic nanoparticles. These PMSAILs have inherent unique ionic liquid properties and self-assembled into various nano-aggregates such as micelles, vesicles, rod-like micelles, and etc., by modification in the structure of cations or anions. PMSAILs provide stimuli-responsive properties, which is one of the essential aspects of targeted applications. The appropriate functional tunability of anions and cations in PMSAILs leads to various multifaceted chemical and biological applications. A new emerging trend in PMSAIL research is hybridization with flexible materials. This review will mainly deal with the synthesis, characterization, and brief history of PMSAILs and their potential advantages in the various applications in micellar catalysis, purification and separation of biomolecules, compaction and decompaction of DNA, drug delivery, and other biomedical applications.     

Rhodium nanoparticles stabilized by ionic copolymers in ionic liquids: long lifetime nanocluster catalysts for benzene hydrogenation

Novel ionic liquid-soluble ionic copolymers containing imidazolium ionic liquidlike units have been synthesized. Rhodium nanoparticles stabilized by the ionic copolymer in ionic liquids have been successfully obtained. The nanoparticles showed unprecedented lifetime and activity in arene hydrogenation under forcing conditions (a temperature of 75 degrees C and a hydrogen pressure of 40 bar) with a total turnover (TTO) of 20 000 (in five total recycles of 4000 TTOs each) and a turnover frequency of 250 h-1, demonstrating that the combination of ionic liquids with ionic liquidlike stabilizers is a pathway towards highly stable and active nanoparticle catalysts.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Fabrication of cerium oxide nanoparticles: characterization and optical properties

Ceria (CeO(2)) is a technologically important rare earth material because of its unique properties and various engineering and biological applications. A facile and rapid method has been developed to prepare ceria nanoparticles using microwave with the average size 7 nm in the presence of a set of ionic liquids based on the bis (trifluoromethylsulfonyl) imide anion and different cations of 1-alkyl-3-methyl-imidazolium. The structural features and optical properties of the nanoparticles were determined in depth with X-ray powder diffraction, transmission electron microscope, N(2) adsorption-desorption technique, dynamic light scattering (DLS) analysis, FTIR spectroscopy, Raman spectroscopy, UV-vis absorption spectroscopy, and Diffuse reflectance spectroscopy. The energy band gap measurements of nanoparticles of ceria have been carried out by UV-visible absorption spectroscopy and diffuse reflectance spectroscopy. The surface charge properties of colloidal ceria dispersions in ethylene glycol have been also studied. To the best of our knowledge, this is the first report on using this type of ionic liquids in ceria nanoparticle synthesis.     

Imidazolium-functionalized bipyridine derivatives: a promising family of ligands for catalytical Rh(0) colloids

A new imidazolium-monofunctionalized bipyridine ligand has been synthesized and efficiently used as a protective agent for Rh(0) nanoparticles. Preliminary results in arene hydrogenation have been obtained.