Luís M. N. B. F. Santos

Abstract The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.

Abstract An experimental and theoretical study of solution and solvation of mono-and divalent alkali metal cations in the protic ionic liquid (IL) ethylammonium nitrate (EAN) is reported. High precision solution-reaction calorimetry was used to obtain the heat of solvation, which was used for the analysis of the thermodynamics. A close relation between the structure of the salts in the crystalline phase and its enthalpy of solvation in the IL is reported. A detailed picture of the molecular environments in the solvation shells around the metal cations is provided by means of molecular dynamics simulations. The analysis of the energetics and structure of solvation confirms the well-known water-like solvation properties of EAN, with the solvation shell around the metal cations in both media being very similar. On the other hand, the results show that it is energetically more favourable to solvate smaller cations with higher valence. Indeed, the simulations show that the long-range electrostatic interactions are the main contribution to solvation interaction, with the electric field at the surface of the alkali metal cations as the basic magnitude controlling it.

Abstract This work reports the thermodynamic and morphological study and characterization of four salts consisting of a divalent/trivalent cobalt complex with pyrazole-pyridine ligands (FK 102 and FK 209 samples) and bis(trifluoromethylsulfonyl)imide (TFSI) moieties as counter anions. The oxidation state of the central metal (Co(II) or Co(III)) and the presence of tert-butyl (t-Bu) groups in the ligand structure were found to have a strong impact on the thermal behavior, phase stability, heat capacities, and thin-film morphology of each salt. The Co(II) complexes exhibited good thermal stability up to 600 K. Lower thermal stability was observed for the Co(III) congeners. The FK 209 Co(III) displayed a higher melting temperature but a partial decomposition during or above melting was detected. The higher melting temperatures observed for the Co(III) complexes were found to be entropically driven. However, the addition of t-Bu in the ligand (FK 209) leads to an increase in the melting temperature, which is driven by the enthalpy of fusion. The four compounds studied evidenced a large glass-forming ability. Moreover, the thermal stability of the glassy state was clearly increased when the ligands comprised t-Bu groups. The contribution of the t-Bu group for the molar heat capacity in the solid phase, at T = 298.15 K, was found to be (110 ± 3) J·K−1·mol−1 and (98 ± 4) J·K−1·mol−1 for the Co(II) and Co(III) complexes, respectively. These results are in good agreement with the contribution of the t-Bu group observed for both solid and liquid phases in other materials, indicating that the t-Bu groups are relatively unhindered in the crystalline phase of the salts. The morphological behavior of the thin films of FK 102 samples was found to be quite similar to the observed for typical ionic liquids, with the formation of micro- and nanodroplets onto different substrates. The introduction of t-Bu substituents in the ligand structure was found to have a strong impact on the formation of homogeneous and compact nanofilms for the FK 209 salts. © 2022 Elsevier Ltd

Abstract This work presents the effect of methylation in the C2 position of the imidazolium in the cohesive interaction of trifluoromethanesulfonate ionic liquids (ILs). The effect of C2 methylation was evaluated and analyzed by comparison between the C2-methylated and C2-protonated analogues. It was found that the nature of the anion has a strong impact on the differentiation of the effect of the C2-methylation. While strong-coordinating and smaller anions promote the hydrogen bonding interaction with the acidic hydrogen at the C2 position of the imidazolium ring, for the case of a weak-coordinating and larger anions, the C2-methylation is expected to have a dominant contribution in the decrease of the liquid entropy, associated with the decrease of the anion-around-cation dynamics due to the presence of the bulkier methyl group (-CH3) in the position 2. The volatility, heat capacities, thermal stability, and phase behavior are presented for two ionic liquids methylated at the C2 position of imidazolium ring [(1)C(2)(2)C(1)(3)C(1)im][OTf] and [(1)C(4)(2)C(1)(3)C(1)im][OTf], and their. C2-protonated analogues [(1)C(2)(3)C(1)im][OTf] and [(1)C(4)(3)C(1)im][OTf]. It was found that the C2 methylation has a quite low impact on the volatility, due to an enthalpic - entropic compensation effect. However, the derived thermodynamic properties indicate a decrease of enthalpy and entropy of vaporization with the methylation at the C2 position, which is consistent with the existence of hydrogen bond interactions in the. C2-protonated [OTf]-based ILs. The methylation at position 2 of the imidazolium leads to an increase in the melting temperature. This effect is especially significant between [(1)C(2)(3)C(1)im][OTf] and [(1)C(2)(2)C(1)(3)C(1)im] [OTf] with an increase of 125 K in melting temperature. The experimental results suggest that this behavior is associated with an increase of enthalpy of fusion due to the substitution of the hydrogen at the C2 position by the bulkier methyl group (-CH3).