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A panel of metal–betaine–bistriflimide complexes (with minimum formula M[Bet]2[Tf2N]2, where M = Mg, Ca, Zn, Cu and Ni) has been prepared in high purity and a quantitative yield. In parallel, a series of metal bistriflimide salts (sharing the same metal cations) has been synthesized and characterized though the same set of techniques. The current work presents a first comprehensive investigation of the physical–chemical properties of these two classes of metal systems, whose importance in a variety of applicative fields was not yet matched, to the best of our knowledge, by an adequate study of their characteristics. All the considered compounds have been spectroscopically, thermally and electrochemically characterized, and their solubility characteristics assessed, gaining insights into the role of metal cations in the definition of their properties. On the other hand, the evident effect of the betaine coordination on the prepared complexes' solubility, thermal stability, melting point, glass and solid–solid transitions, redox behaviour and electrochemical window was ascertained, providing results which would allow a more informed use and application of these classes of divalent metal complexes. [ABSTRACT FROM AUTHOR]

A panel of novel vanadium(IV)–betaine complexes has been synthesized according to new and efficient methodologies and characterized through both spectroscopic techniques and thermal analyses. Vanadium(IV)–betaine solutions have been electrochemically oxidized and the effect of betaine ligands on the thermal and pH stability of vanadium(V) solutions has been evaluated under different temperature and acidity conditions. The obtained results displayed a remarkable effect for both of the examined parameters, achieving the preparation of aqueous vanadium(V) solutions displaying long term stability at more than 55 °C under mild acidic conditions. The species formed in the betaine rich vanadium(V) solutions have been sprectroscopically identified in relationship with the acidity of the solution, and the obtained results were confirmed through computational techniques. Vanadium–betaine based solutions have been finally tested in a lab-scale redox flow battery setup, providing preliminary insight into the possible use of this type of electrolyte in VRFBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electrochemical stability of ionic liquids comprising ammonium cations and Tf 2 N anion was determined at −33 °C. • The increase of alkyl long chain length in the cations decreases the stability windows for both cathodic and anodic voltages. • The cathodic windows of ether chains ionic liquids look higher than the ones of alkyl chain compounds. • Ionic liquids having alkyl chains show wider anodic limits than ionic liquids with ether chains. • Ammonium cations having one short chain with a different length than the other two showed the widest electrochemical stability. Ionic gating has emerged as an effective and versatile tool to tune the charge-carrier density of a material and control its electronic ground state, as well as to develop low-temperature devices such as electrochemical transistors. Ionic liquids are a promising gating agent due to their high thermal- and electrochemical stability for both fundamental and applied research. However, the understanding of the correlation between the molecular structure of ionic liquids and their electrochemical stability is quite limited. For this reason, this study aims at determining the guidelines for synthesizing ionic liquids suitable for their use as electrolytes at low temperatures. A series of twenty-three ionic liquids having various ammonium cations, composed of three ''short chains'' and one ''long chain'', and Tf 2 N as the anion, were synthesized. Afterwards, their thermal behavior was determined to identify those ionic liquids exhibiting T g < −50 °C. The anodic and cathodic limits of the selected ionic liquids were measured via linear-sweep voltammetry using an electrochemical transistor configuration, working at −33 °C. Electrochemical windows having absolute values from 2.9 to 5.7 V were measured. Overall, five guidelines were determined from the experimental results: first, the cations influence both cathodic and anodic limits; second, the asymmetric ammonium cations show larger electrochemical stability than symmetric ones; third, the electrochemical stability decreases at the increase of the length of the ''long chain''; fourth, alkyl long chains show a larger anodic limit, but smaller cathodic limit than ether long chains having the same length; fifth, the ether chain with largest electrochemical stability comprises three carbon atoms and one oxygen. [ABSTRACT FROM AUTHOR]

[Display omitted] • Seven selected levulinate ILs (LevILs) featuring different cations have been prepared. • The thermal behaviour was investigated through TG and DSC techniques. • The viscosity of LevILs as a function of temperature was analysed. • The glassy behaviour of the LevILs was evaluated using the MYEGA viscosity model. • The refractive index was determined at different wavelengths and temperatures. In the context of bio-based ionic liquids (ILs), in recent years levulinate ILs have been explored in various applications with appreciable performances. To expand their scope of use, seven selected levulinate ILs featuring different cationic moieties have been prepared and their physico-chemical properties compared. While all the ILs generated displayed only glass transitions at low temperature (<−60 °C), [C 4 C 1 Pyr]Lev presented melting and crystallization events. The thermal stability determined by TGA decreased in the order [P 8881 ]Lev > [C 2 C 1 Im]Lev ≈ [C 4 C 1 Im]Lev > [C 2 C 1 Pip]Lev > [C 2 C 1 Pyr]Lev ≈ [C 4 C 1 Pyr]Lev > [N 8881 ]Lev, and is in good agreement with the general trend observed for carboxylate ILs. In terms of viscosity, the LevILs showed a Newtonian behaviour when considering the shearing rates range, with a marked reduction of the viscosity at increasing temperatures. The glassy behaviour of LevILs was further ascertained applying the MYEGA viscosity-based model for the determination of the fragility index. The density of the LevILs was found to vary in the vicinity of 1 g / cm 3 , and the systematic refractive index increase with increasing density was identified as a general trend. The refractive index was experimentally determined at five different wavelengths and several temperatures between 80 °C and 130 °C and followed the order [C 2 C 1 Im]Lev > [C 2 C 1 Pip]Lev > [C 4 C 1 Im]Lev > [C 2 C 1 Pyr]Lev > [C 4 C 1 Pyr]Lev > [P 8881 ]Lev > [N 8881 ]Lev. Overall, the possibility to tune the physico-chemical properties of ILs through structural variations of the cationic part has been proven valid for the LevIL family. When compared with the carboxylate ILs described in the literature, LevILs show great potential for further applicative studies. [ABSTRACT FROM AUTHOR]

Benzimidazole dicationic ionic liquids (BDILs) have not yet been widely explored in spite of their potential. Therefore, two structurally related families of BDILs, paired with either bromide or bistriflimide anions and bearing alkyl spacers ranging from C3 to C6, have been prepared. Their thermal properties have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), while their electrical properties have been assessed by cyclic voltammetry (CV). TG analysis confirmed the higher stability of the bistriflimide BDILs over the bromide BDILs, with minor variation within the two families. Conversely, DSC and CV allowed for ascertaining the role played by the spacer length. In particular, the thermal behavior changed dramatically among the members of the bistriflimide family, and all three possible thermal behavior types of ILs were observed. Furthermore, cyclic voltammetry showed different electrochemical window (C3(C1BenzIm)2/2Tf2N < C4(C1BenzIm)2/2Tf2N, C5(C1BenzIm)2/2Tf2N < C6(C1BenzIm)2/2Tf2N) as well as a reduction peak potential, shape, and intensity as a function of the spacer length. The results obtained highlight the benefit of accessing a more structurally diverse pool of compounds offered by dicationic ILs when compared to the parent monocationic ILs. In particular, gains are to be found in the ease of fine-tuning their properties, which translates in facilitating further investigations toward BDILs as designer solvents and catalysts. [ABSTRACT FROM AUTHOR]