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In this study, X-ray photoelectron spectroscopy is used to analyse nine morpholinium ionic liquids, which are of great interest in green chemistry because of their low toxicity and high recyclability. The effect of alkyl chain length on the aliphatic C 1s binding energies is studied. The impact of the anion basicity on the cationic N 1s and O 1s binding energies is investigated. It is concluded that by changing the basicity of the anion, there is a more noticeable change in the electronic environment of the oxygen centre. The effect of the long alkyl side substituent on the cation-anion interactions is also discussed. It is observed that there is an intense charge shielding effect of the alkyl side chain in the cases of octyl and dodecyl, which is reflected in lowering of the measured Br 3d5/2 binding energy.

The two major properties that underpin ionic liquids are tunability and the potential to create task-specific media. Together, these properties allow ionic liquids to surpass the roles long held by traditional molecular solvents. However, at elevated temperatures or under prolonged heating, the structural components that impart such properties decompose or degrade. Dicationic pyridine salts present new opportunities to extend functionality and tunability to high temperatures because they are coordinating and thermally robust. In this work, we present three structurally related series of dicationic pyridine salts, which have been characterized by a wide array of techniques to link thermal and electronic properties to structural variation. The phase transitions and thermal stabilities of the salts were significantly influenced by small structural changes, and several new candidates for high-temperature-based applications were identified. The electron density, and therefore the electron donating ability, of the pyridine functional group could also be controlled by structural variation of cations and anions. Therefore, dicationic pyridine salts are highly tunable choices for task-specific solvents at elevated temperatures. Importantly, thermally robust solvents not only extend operational ranges but also reduce the need to replace or replenish solvents that degrade over time at temperatures commonly employed in industrial settings (i.e., 150−200 °C); solvent lifetimes are extended, and production is reduced. This is a critical requirement for complex media such as ionic liquids, which have high economic and environmental production costs.

With the aim of obtaining thermochromic systems with potential applications in solar energy storage, we evaluated the behavior of some sugar-based ionic liquids (ILs)-Co(NTf2)2 complexes, in IL solution, as a function of temperature. Different structural changes on the cation, the nature of the anion, and the nature of the IL used as the solvent were considered. The analysis of the above factors was carried out through a combined approach of different techniques, that is, variable temperature UV-vis and NMR spectroscopies, conductivity, and thermal gravimetric analysis. The thermochromic systems were analyzed both as solutions and as thin films, and the data collected highlight the defining role played by both the cation structure and the solvent nature in determining their performance. Most of the investigated systems show a chromogenic transition from pink to blue, occurring in a temperature range suitable for practical applications (40-60 °C). Interestingly, when embedded in a polymeric matrix, thin films with high recyclability and long life are also described.

A range of dialkylimidazolium organotrifluoroborate ionic liquids were prepared by anion metathesis from newly available potassium organotrifluoroborate salts, and their physical properties were characterized by TGA, DSC, and STA. Thermal decomposition was subsequently investigated under vacuum with direct insertion mass spectrometry to determine whether thermolysis was a viable route to prepare N-heterocyclic carbene organofluoroborates, which are an important class of emerging compounds. Several key targets were identified, which highlighted the potential to shortcut complex synthetic methodologies otherwise required to access such molecules.

In this study, X-ray photoelectron spectroscopy is used to probe the impact of the N3-substituted alkyl group on the electronic environment of the cation and the anion by comparing two types of imidazolium cations, 1-alkyl-3-butylimidazolium and 1-alkyl-3-methylimidazolium. Due to the more intense inductive effect changing from methyl to butyl, the electronic environment of the cationic nitrogen can be significantly affected, which is reflected in a shift of N 1s binding energy. The magnitude of the binding energy shift is found to be more pronounced in the case of the less basic anion and inversely proportional to the basicity of the anion. The increase of the N3-substituted alkyl chain length can also influence the charge-transfer effect from the anion to the cation. This gives rise to a change in the electronic environment of the anion. Such an impact is found to be concentrated on the anion-based component bearing more negative point charges.

X-ray photoelectron spectroscopy is used to investigate the impact of methylation on the electronic environment of pyridinium cations. Because of the electron-donating effect of the methyl group, there is a significant increase in electron density on the cationic nitrogen. The shift of the N 1s binding energy is inversely proportional to the anion basicity. The methylation position on the electronic environment of the cationic nitrogen is investigated. The N 1s binding energy follows the trend: 1-octylpyridinium > 1-octyl-3-picolinium > 1-octyl-4-picolinium > 1-octyl-2-picolinium, which is in good agreement with the cation acidity. The increase in the inductive effect subsequently weakens the cation-anion interactions through charge transfer from the anion to the cation, causing a subtle change in the electronic environment of the anion. Such an effect is noticeably reflected in the Br 3d binding energy. It shows that the Br 3d5/2 binding energy of 1-octyl-2-picolinium bromide is 0.2 eV lower than that of 1-octylpyridinium bromide.

In this study, nine piperidinium-based ionic liquids are analysed by X-ray photoelectron spectroscopy. The effect of alkyl substituent length and the nature of the anion on the electronic environment of the cation are investigated. The electronic environment of the hetero carbon and the cationic nitrogen is compared between two structurally similar cations, 1-octyl-1-methylpiperidinium ([C8C1Pip]+)versus1-octylpyridinium ([C8Py]+). Due to the charge delocalisation, the hetero carbon component within [C8Py]+is more positively charged, which exhibits much higher binding energy; whilst the cationic nitrogen component is in the similar electronic environment. The impact of the charge delocalisation on the electronic environment of the anion is also compared between [C8C1Pip]+and [C8Py]+. It is found that for the more basic anion, the cation can significantly affect the electronic environment of the anion; for the less basic anion, such an effect concentrates on the component bearing more negative point charges.

The charge distribution associated with individual components in functionalised ionic liquids (ILs) can be tuned by careful manipulation of the substituent groups incorporated into the ions. Here we use X-ray photoelectron spectroscopy to investigate the impact of substituent atoms on the electronic structure of similar imidazolium-based systems each paired with a common anion, [Tf2N]-. The experimental measurements revealed an unexpected variation in the charge density distribution within the IL cation when the oxygen atom in a poly-ether containing side chain is moved by just one atomic position. This surprising observation is supported by density functional theory calculations.

ispartof: ACS SUSTAINABLE CHEMISTRY & ENGINEERING vol:8 issue:23 pages:8469-8470 status: published

Until now, much Green and Sustainable Chemistry has been focused on how chemicals are made. Here we suggest that, if chemistry is to contribute effectively to achieving the SDGs, we need to change the way that things are done at both ends of the chemical supply chain. For chemical research at the start of the chain, we need to rethink how we build the laboratories in which we carry out the research so as to minimize the use of energy. At the other end of the chain, we advocate the adoption of a Moore's Law for Chemistry (MLFC), which we recently proposed that, wherever possible, the amount of chemical(s) used to achieve a given effect should be decreased by a factor of 2 every five years.

One of the reasons why ionic liquids have received growing interest from researchers is their environmentally interesting characteristics, such as their negligible vapour pressure and their good chemical and thermal properties. In particular, dicationic ionic liquids whose thermal and electrochemical stability is higher than that of monocationic ionic liquids have begun to gain attention during recent years. In this work, monocationic and dicationic ionic liquids were synthesized, characterized and tested for their toxicity, which was assessed using the luminescent bacterium Vibrio fischeri. The results revealed that the toxicity of the ionic liquids mainly depends on the head groups and linkage chain length of their cationic structure. Introduction of a new cationic head decreased the EC50 (concentration which leads to 50% reduction in bioluminescence of the bacteria) of the ionic liquids. The results present a promising picture of dicationic ionic liquids as alternatives with lower environmental impact than their monocationic counterparts and underline the significance of designing particular structures for ionic liquids.

We use X-ray photoelectron spectroscopy (XPS) to identify the interaction between the rhodium atom and phosphine ligands in six 1-octyl-3-methylimidazolium-based ionic liquids ([C8C1Im][X]). The formation of a mono-phosphine rhodium complex based upon addition of triphenylphosphine (PPh3) is confirmed by XPS in all ionic liquids studied herein. Due to the electron donation effect of the ligand, the rhodium atom becomes more negatively charged and thus exhibits a lower measured binding energy. The influence of the anion basicity on the formation of different types of rhodium complexes is also investigated. By introducing a biphosphine ligand, a chelated diphosphine rhodium complex is formed in ionic liquids with more basic anions and verified by both XPS and Infrared Spectroscopy (IR). The measured Rh 3d binding energies are correlated to the reaction selectivity of a hydroformylation reaction which inspires a method to design a metal catalyst to control the chemical reaction towards desired products in the future.

The electronic environment of the metal centre of a catalyst dissolved in ionic liquids has a determining effect on its catalytic efficiency in chemical reactions. However, the electronic environment of the ionic liquid-based metal centres can be influenced by not only their chemical state but also the solute–solvent interaction. In this work, we demonstrate that the anion of an ionic liquid can significantly influence the electronic environment of a metal centre. The metal centre electronic environment can be monitored by measuring the typical electron binding energies by X-ray photoelectron spectroscopy (XPS). The correlation of the electronic environment of the metal centre with reaction performance provides a possibility to design and control a chemical reaction. In this work, we also illustrate a strategy for tuning the electronic environment of metal centres, by the selection of particular ionic liquid anions, to design a catalytic system and consequently to finally control the reaction performance of a model Suzuki cross coupling reaction.

In this work, binary mixtures of a non-ionic surfactant (Triton X-100) and water were studied with concentrations of 30%wt H2O, showing, lamellar mesophase at temperatures below 10oC. Different dicationic ionic liquids were used for doping these mesophases: 1,n-bis(3-methylimidazolium-1-yl)alkane, 1,n-bis(1-methylpyrrolidinium-1-yl)alkane and 1,n-bis(pyridinium-N-yl)alkane dibromide, where n = 6 and 8. Polarized Optical Microscopy and Small-Angle X-ray Scattering were used for identifying the mesophases and the influence of different dicationic ionic liquids on the lyotropic liquid crystals phase transitions. The addition of dicationic ionic liquids to the lyotropic liquid crystals samples led to changes in transition temperature and in mesophase structure itself (such as characteristic distances).