1
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Silva R, Montes-Campos H, Lobo Ferreira AI, Bakis E, Santos LM. Thermodynamic Study of Alkylsilane and Alkylsiloxane-Based Ionic Liquids. J Phys Chem B 2024; 128:3742-3754. [PMID: 38573787 PMCID: PMC11033869 DOI: 10.1021/acs.jpcb.3c08333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 02/23/2024] [Accepted: 03/20/2024] [Indexed: 04/06/2024]
Abstract
The thermodynamic properties of ionic liquids (ILs) bearing alkylsilane and alkylsiloxane chains, as well as their carbon-based analogs, were investigated. Effects such as the replacement of carbon atoms by silicon atoms, the introduction of a siloxane linkage, and the length of the alkylsilane chain were explored. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal and phase behavior (glass transition temperature, melting point, enthalpy and entropy of fusion, and thermal stability). Heat capacity was obtained by high-precision drop calorimetry and differential scanning microcalorimetry. The volatility and cohesive energy of these ILs were investigated via the Knudsen effusion method coupled with a quartz crystal microbalance (KEQCM). Gas phase energetics and structure were also studied to obtain the gas phase heat capacity as well as the energy profile associated with the rotation of the IL side chain. The computational study suggested the existence of an intramolecular interaction in the alkylsiloxane-based IL. The obtained glass transition temperatures seem to follow the trend of chain flexibility. An increase of the alkylsilane chain leads to a seemingly linear increase in molar heat capacity. A regular increment of 30 J·K-1·mol-1 in the molar heat capacity was found for the replacement of carbon by silicon in the IL alkyl chain. The alkylsilane series was revealed to be slightly more volatile than its carbon-based analogs. A further increase in volatility was found for the alkylsiloxane-based IL, which is likely related to the decrease of the cohesive energy due to the existence of an intramolecular interaction between the siloxane linkage and the imidazolium headgroup. The use of Si in the IL structure is a suitable way to significantly reduce the IL's viscosity while preserving its large liquid range (low melting point and high thermal stability) and low volatilities.
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Affiliation(s)
- Rodrigo
M.A. Silva
- CIQUP,
Institute of Molecular Sciences (IMS), Department of Chemistry and
Biochemistry, Faculty of Science, University
of Porto, Rua do Campo Alegre, Porto 4169-007, Portugal
| | - Hadrián Montes-Campos
- CIQUP,
Institute of Molecular Sciences (IMS), Department of Chemistry and
Biochemistry, Faculty of Science, University
of Porto, Rua do Campo Alegre, Porto 4169-007, Portugal
| | - Ana I.M.C. Lobo Ferreira
- CIQUP,
Institute of Molecular Sciences (IMS), Department of Chemistry and
Biochemistry, Faculty of Science, University
of Porto, Rua do Campo Alegre, Porto 4169-007, Portugal
| | - Eduards Bakis
- Faculty
of Chemistry, University of Latvia, Jelgavas 1, Riga LV-1004, Latvia
| | - Luís M.N.B.F. Santos
- CIQUP,
Institute of Molecular Sciences (IMS), Department of Chemistry and
Biochemistry, Faculty of Science, University
of Porto, Rua do Campo Alegre, Porto 4169-007, Portugal
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2
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Bo Z, Zhang X, Huang Z, Huang Y, Yan J, Cen K, Yang H. Binary ionic liquids hybrid electrolyte based supercapacitors with high energy & power density. RSC Adv 2023; 13:15762-15771. [PMID: 37235105 PMCID: PMC10206612 DOI: 10.1039/d3ra01634j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023] Open
Abstract
Supercapacitors with high energy and power densities have become highly desirable in practical applications. Ionic liquids (ILs) are considered as promising electrolytes of supercapacitors owing to their excellent electrochemical stability window (approx. 4-6 V) and good thermal stability. However, the high viscosity (up to 102 mPa s) and low electric conductivity (<10 mS cm-1) at room-temperature extremely reduce the ion diffusion dynamics in the energy storage process, resulting in the unsatisfactory power density and rate performance of supercapacitors. Herein we propose a novel binary ionic liquids (BILs) hybrid electrolyte composed of two kinds of ILs in an organic solvent. Along with the organic solvent with high dielectric constant and low viscosity, the addition of binary cations effectively improves the electric conductivity and reduces the viscosity of IL electrolytes. By mixing trimethyl propylammonium bis(trifluoromethanesulfonyl)imide ([TMPA][TFSI]) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Pyr14][TFSI]) with an equal mole ratio in acetonitrile (1 M), the as-prepared BILs electrolyte shows superior electric conductivity (44.3 mS cm-1), low viscosity (0.692 mPa s), and a wide electrochemical stability window (4.82 V). The supercapacitors assembled with activated carbon electrodes (commercial mass loading) and this BILs electrolyte achieve a high working voltage of 3.1 V, leading to a maximum energy density of 28.3 W h kg-1 at 803.35 W kg-1 and a maximum power density of 32.16 kW kg-1 at 21.17 W h kg-1, which are obviously superior to those of commercial supercapacitors based on organic electrolytes (2.7 V).
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Affiliation(s)
- Zheng Bo
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
| | - Xu Zhang
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
| | - Zhesong Huang
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
| | - Yuhui Huang
- College of Materials Science and Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
- Research Institute of Zhejiang University-Taizhou Taizhou Zhejiang Province 318000 China
| | - Jianhua Yan
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
| | - Kefa Cen
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
| | - Huachao Yang
- State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, College of Energy Engineering, Zhejiang University Hangzhou 310027 Zhejiang China
- Research Institute of Zhejiang University-Taizhou Taizhou Zhejiang Province 318000 China
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3
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O'Brien RA, Hillesheim PC, Soltani M, Badilla-Nunez KJ, Siu B, Musozoda M, West KN, Davis JH, Mirjafari A. Cyclopropane as an Unsaturation "Effect Isostere": Lowering the Melting Points in Lipid-like Ionic Liquids. J Phys Chem B 2023; 127:1429-1442. [PMID: 36745872 DOI: 10.1021/acs.jpcb.2c07872] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The replacement of unsaturation with a cyclopropane motif as a (bio)isostere is a widespread strategy in bacteria to tune the fluidity of lipid bilayers and protect membranes when exposed to adverse environmental conditions, e.g., high temperature, low pH, etc. Inspired by this phenomenon, we herein address the relative effect of the cyclopropanation, both cis and trans configurations, on melting points, packing efficiency, and order of a series of lipid-like ionic liquids via a combination of thermophysical analysis, X-ray crystallography, and computational modeling. The data indicate there is considerable structural latitude possible when designing highly lipophilic ionic liquids that exhibit low melting points. While cyclopropanation of the lipid-like ionic liquids provides more resistance to aerobic degradation than their olefin analogs, the impact on the melting point decrease is not as pronounced. Our results demonstrate that incorporating one or more cyclopropyl moieties in long aliphatic chains of imidazolium-based ionic liquids is highly effective in lowering the melting points of such materials relative to their counterparts bearing linear, saturated, or thioether side chains. It is shown that the cyclopropane moiety effectively disrupts packing, favoring formation of gauche conformer in the side chains, resulting in enhancement of fluidity. This was irrespective of the configuration of the methylene bridge, although marked differences in the effect of cis- and trans-monocyclopropanated ILs on the melting points were observed.
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Affiliation(s)
- Richard A O'Brien
- Department of Chemistry, The University of South Alabama, Mobile, Alabama 36688, United States
| | - Patrick C Hillesheim
- Department of Chemistry and Physics, Ave Maria University, Ave Maria, Florida 34142, United States
| | - Mohammad Soltani
- Department of Chemistry, The University of South Alabama, Mobile, Alabama 36688, United States
| | - Kelly J Badilla-Nunez
- Department of Chemical and Biomolecular Engineering, The University of South Alabama, Mobile, Alabama 36688, United States
| | - Ben Siu
- Department of Chemical and Biomolecular Engineering, The University of South Alabama, Mobile, Alabama 36688, United States
| | - Muhammadiqboli Musozoda
- Department of Chemistry, State University of New York at Oswego, Oswego, New York 13126, United States
| | - Kevin N West
- Department of Chemical and Biomolecular Engineering, The University of South Alabama, Mobile, Alabama 36688, United States
| | - James H Davis
- Department of Chemistry, The University of South Alabama, Mobile, Alabama 36688, United States
| | - Arsalan Mirjafari
- Department of Chemistry, State University of New York at Oswego, Oswego, New York 13126, United States
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4
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New task-specific ionic liquids based on phenyl diazenyl methyl pyridinium cation: Energetic, electronic and optical properties exploration based on DFT calculations. J Mol Graph Model 2023; 118:108352. [DOI: 10.1016/j.jmgm.2022.108352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2022] [Revised: 09/18/2022] [Accepted: 09/27/2022] [Indexed: 11/06/2022]
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5
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Guan Y, Clark R, Philippi F, Zhang X, Welton T. How do external forces related to mass and charge affect the structures and dynamics of an ionic liquid?. J Chem Phys 2022; 156:204312. [DOI: 10.1063/5.0091322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ionic liquids (ILs) are novel promising materials widely used in various fields. Their structures and properties can be tuned by means of external perturbations, thus further broadening their applications. Herein, forces proportional to atomic mass (mass-related field) and atomic charge (electric field) are applied in molecular dynamics simulations to the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to investigate the origin of the resulting changes in structures and dynamics. The results show that both electric and mass-related fields cause the ion cages to expand and deform, eventually leading to their breakdown to produce a transformation of IL from cage structure to channel-like structure, which results in faster self-diffusion of ions in the directions of the applied force and to a lesser extent other directions. Further comparison of electric and mass-related fields demonstrates that only the electric fields reorientate cations to produce a hydrodynamically favoured conformation in the force direction which shows faster diffusion. The cis isomer of the anion is preferred in the presence of the electric fields, whereas applying the forces proportional to mass does not change the anion conformer equilibrium significantly. The results presented in this work aid in the understanding of how ions adjust their structures to adapt to external perturbations and facilitates the application of ILs as electrolytes.
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Affiliation(s)
- Yongji Guan
- School of Information Science and Engineering, Lanzhou University, China
| | - Ryan Clark
- Imperial College Department of Chemistry, United Kingdom
| | | | - Xiaoping Zhang
- School of Information Science and Engineering, Lanzhou University, China
| | - Thomas Welton
- Department of Chemistry, Imperial College London, United Kingdom
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6
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Koutsoukos S, Philippi F, Rauber D, Pugh D, Kay CWM, Welton T. Effect of the cation structure on the properties of homobaric imidazolium ionic liquids. Phys Chem Chem Phys 2022; 24:6453-6468. [PMID: 35244651 DOI: 10.1039/d1cp05169e] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In this work we investigate the structure-property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C2 position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues.
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Affiliation(s)
- Spyridon Koutsoukos
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK.
| | - Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK.
| | - Daniel Rauber
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany
| | - David Pugh
- Department of Chemistry, Britannia House, Kings College London, 7 Trinity Street, London SE1 1DB, UK
| | - Christopher W M Kay
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany.,London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK.
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7
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Tran L, Rush K, Marzette J, Edmonds-Andrews G, Bennett T, Abdulahad A, Riley KE, Dutta S. Striking temperature-dependent molecular reorganization at the C-2 position of [EMIM][BF4]. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2021.138956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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8
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Mahapatra A, Chakraborty M, Barik S, Sarkar M. Comparison between pyrrolidinium-based and imidazolium-based dicationic ionic liquids: intermolecular interaction, structural organization, and solute dynamics. Phys Chem Chem Phys 2021; 23:21029-21041. [PMID: 34522923 DOI: 10.1039/d1cp02790e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
With an aim to understand the difference in the behaviour of imidazolium and pyrrolidinium-based dicationic ionic liquids (DILs) in terms of the intermolecular interactions, microscopic-structure and dynamics, two DILs, the imidazolium-based 1,9-bis(3-methylimidazolium-1-yl)nonane bis(trifluoromethanesulfonyl)imide and the pyrrolidinium-based 1,9-bis(1-methylpyrrolidinium-1-yl)nonane bis(trifluoromethanesulfonyl)imide, have been synthesized and subsequently investigated by exploiting combined steady sate and time resolved fluorescence, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopic techniques. Data obtained for DILs have also been compared with their corresponding mono-cationic counterpart (MILs) to evaluate and understand the distinctive characteristics of the DILs in contrast with the corresponding MILs. Steady state emission and EPR data have revealed that the pyrrolidinium-based DIL is slightly less polar than the imidazolium-based DIL. Temperature-dependent fluorescence anisotropy decay of two probes, perylene and MPTS (8-methoxypyrene-1,3,6-trisulfonate), has been measured in DILs as well as in MILs. Solute-solvent coupling constants obtained from the experimentally measured rotational correlation times with the aid of Stokes-Einstein-Debye hydrodynamic theory have indicated appreciable differences in the dynamics of both the solutes on going from MILs to DILs. More interestingly, the outcome of the NMR study has suggested that the alkyl spacer chain in the imidazolium-based DIL exists in the folded form, but the pyrrolidinium-based DIL remains in the straight chain conformation. Inherently, the outcomes of all of these studies have depicted that the microscopic structural organisations in imidazolium and pyrrolidinium-based DILs are different from each other as well as from their respective mono-cationic counterparts.
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Affiliation(s)
- Amita Mahapatra
- School of Chemical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, Khurda, 752050, Bhubaneswar, Odisha, India.
| | - Manjari Chakraborty
- School of Chemical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, Khurda, 752050, Bhubaneswar, Odisha, India.
| | - Sahadev Barik
- School of Chemical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, Khurda, 752050, Bhubaneswar, Odisha, India.
| | - Moloy Sarkar
- School of Chemical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, Khurda, 752050, Bhubaneswar, Odisha, India.
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9
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Philippi F, Welton T. Targeted modifications in ionic liquids - from understanding to design. Phys Chem Chem Phys 2021; 23:6993-7021. [PMID: 33876073 DOI: 10.1039/d1cp00216c] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Ionic liquids are extremely versatile and continue to find new applications in academia as well as industry. This versatility is rooted in the manifold of possible ion types, ion combinations, and ion variations. However, to fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituents. In this work, we discuss targeted modifications as a powerful tool to provide understanding and to enable design. A 'targeted modification' is a deliberate change in the structure of an ionic liquid. This includes chemical changes in an experiment as well as changes to the parameterisation in a computer simulation. In any case, such a change must be purposeful to isolate what is of interest, studying, as far as is possible, only one concept at a time. The concepts can then be used as design elements. However, it is often found that several design elements interact with each other - sometimes synergistically, and other times antagonistically. Targeted modifications are a systematic way of navigating these overlaps. We hope this paper shows that understanding ionic liquids requires experimentalists and theoreticians to join forces and provides a tool to tackle the difficult transition from understanding to design.
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Affiliation(s)
- Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK.
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10
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Nishikawa K, Fujii K, Hashimoto Y, Tozaki KI. Unique phase behavior of a room-temperature ionic liquid, trimethylpropylammonium bis(fluorosulfonyl)amide: surface melting and its crystallization. Phys Chem Chem Phys 2020; 22:20634-20642. [PMID: 32966414 DOI: 10.1039/d0cp03073b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The phase behavior of a representative ammonium-based ionic liquid, trimethylpropylammonium bis(fluorosulfonyl)amide ([N1113][FSA]), was investigated using a laboratory-made differential scanning calorimeter (DSC). The apparatus possesses extremely high sensitivities with stability of ±2 nW in thermal flux and ±1 mK in temperature and a very slow scanning rate of 0.001 mK s-1 in the slowest scanning speed. Besides two ordinary signals from crystallization and melting, a very weak exothermic peak, 1/1000 times that of the main crystallization peak, was observed during the cooling process. The peak was assigned to the crystallization of the surface-melting layer. Both the normal and novel crystallizations occurred during the structural relaxation process. The thickness of the surface-melting layer was estimated to be roughly 70-200 nm. To study the details of the melting processes, DSC experiments were performed with very slow scanning rates (0.02 and 0.03 mK s-1). Two novel endothermic peaks were found in the usual melting trace for the sample with the surface crystallization, and no unusual peaks were observed in the sample without the surface crystallization. We believe that the structure of the surface crystallization phase is different from that of the bulk crystalline phase.
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Affiliation(s)
- Keiko Nishikawa
- Toyota Physical & Chemical Research Institute, Nagakute, Aichi 480-1192, Japan. and Graduate School of Science, Chiba University, Chiba, Chiba 263-8522, Japan
| | - Kozo Fujii
- Graduate School of Science, Chiba University, Chiba, Chiba 263-8522, Japan
| | - Yusuke Hashimoto
- WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
| | - Ken-Ichi Tozaki
- Faculty of Education, Chiba University, Chiba, Chiba 263-8522, Japan
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11
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Endo T, Higuchi T, Kimura Y. DFT Study on Conformation of 1-Alkyl-3-methylimidazolium with Ethyl, Propyl, Butyl, Pentyl, and Hexyl Group. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2020. [DOI: 10.1246/bcsj.20200022] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Takatsugu Endo
- Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
| | - Tomoki Higuchi
- Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
| | - Yoshifumi Kimura
- Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
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12
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Yoshii K, Uto T, Tachikawa N, Katayama Y. The effects of the position of the ether oxygen atom in pyrrolidinium-based room temperature ionic liquids on their physicochemical properties. Phys Chem Chem Phys 2020; 22:19480-19491. [DOI: 10.1039/d0cp02662j] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A joint computational and experimental approach uncovered that the position effect of the ether oxygen atom in pyrrolidinium-based room temperature ionic liquids on the physicochemical properties.
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Affiliation(s)
- Kazuki Yoshii
- Department of Applied Chemistry
- Faculty of Science and Technology
- Yokohama
- Japan
- Department of Energy and Environment
| | - Takuya Uto
- Organization for Promotion of Tenure Track
- University of Miyazaki
- Miyazaki 889-2192
- Japan
| | - Naoki Tachikawa
- Department of Applied Chemistry
- Faculty of Science and Technology
- Yokohama
- Japan
| | - Yasushi Katayama
- Department of Applied Chemistry
- Faculty of Science and Technology
- Yokohama
- Japan
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13
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Lima TA, Faria LF, Paschoal VH, Ribeiro MC. Exploring the phase diagram of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesufonyl)imide. J Mol Struct 2019. [DOI: 10.1016/j.molstruc.2019.01.076] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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14
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Endo T, Fujii K, Nishikawa K. Crystal Polymorphism of 1-Butyl-3-methylimidazolium Hexafluorophosphate: Phase Diagram, Structure, and Dynamics. Aust J Chem 2019. [DOI: 10.1071/ch18422] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6), is one of the most representative ILs. Despite its relatively simple ion structure and popularity, [C4mim]PF6 shows complex and confusing thermal phase behaviours, which stem from crystal polymorphism associated with cation conformational change and large thermal hysteresis. To the best of our knowledge, [C4mim]PF6 is the most investigated IL in terms of phase diagram, whereas full understanding has not yet been achieved due to its complexity. Here we review the current status of understanding of the phase diagram and structure/dynamics of each crystalline phase. Presently, depending on temperature and pressure, five structurally different polymorphic crystals have been reported as α, β, γ, δ, and δ’ in addition to some unspecified phases implied by calorimetric studies. Particularly for the α, β and γ phases, the structure and dynamics are well investigated by Raman, NMR, and X-ray scattering techniques.
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15
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Abstract
Vibrational spectroscopy has continued use as a powerful tool to characterize ionic liquids since the literature on room temperature molten salts experienced the rapid increase in number of publications in the 1990's. In the past years, infrared (IR) and Raman spectroscopies have provided insights on ionic interactions and the resulting liquid structure in ionic liquids. A large body of information is now available concerning vibrational spectra of ionic liquids made of many different combinations of anions and cations, but reviews on this literature are scarce. This review is an attempt at filling this gap. Some basic care needed while recording IR or Raman spectra of ionic liquids is explained. We have reviewed the conceptual basis of theoretical frameworks which have been used to interpret vibrational spectra of ionic liquids, helping the reader to distinguish the scope of application of different methods of calculation. Vibrational frequencies observed in IR and Raman spectra of ionic liquids based on different anions and cations are discussed and eventual disagreements between different sources are critically reviewed. The aim is that the reader can use this information while assigning vibrational spectra of an ionic liquid containing another particular combination of anions and cations. Different applications of IR and Raman spectroscopies are given for both pure ionic liquids and solutions. Further issues addressed in this review are the intermolecular vibrations that are more directly probed by the low-frequency range of IR and Raman spectra and the applications of vibrational spectroscopy in studying phase transitions of ionic liquids.
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Affiliation(s)
- Vitor H Paschoal
- Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo , Av. Prof. Lineu Prestes 748, São Paulo 05508-000, Brazil
| | - Luiz F O Faria
- Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo , Av. Prof. Lineu Prestes 748, São Paulo 05508-000, Brazil
| | - Mauro C C Ribeiro
- Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo , Av. Prof. Lineu Prestes 748, São Paulo 05508-000, Brazil
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