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Hunger L, Al‐Sheakh L, Zaitsau DH, Verevkin SP, Appelhagen A, Villinger A, Ludwig R. Dissecting Noncovalent Interactions in Carboxyl‐Functionalized Ionic Liquids Exhibiting Double and Single Hydrogens Bonds Between Ions of Like Charge. Chemistry 2022; 28:e202200949. [PMID: 35785500 PMCID: PMC9543318 DOI: 10.1002/chem.202200949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Indexed: 11/11/2022]
Affiliation(s)
- Lasse Hunger
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
| | - Loai Al‐Sheakh
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
| | - Dzmitry H. Zaitsau
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
- Department LL&M University of Rostock Albert-Einstein-Str. 25 18059 Rostock Germany
| | - Sergey P. Verevkin
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
- Department LL&M University of Rostock Albert-Einstein-Str. 25 18059 Rostock Germany
| | - Andreas Appelhagen
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
| | - Alexander Villinger
- Institut für Chemie Abteilung für Anorganische Chemie Universität Rostock Albert-Einstein-Str. 3a 18059 Rostock Germany
| | - Ralf Ludwig
- Institut für Chemie Abteilung für Physikalische Chemie Universität Rostock Albert-Einstein-Str. 27 18059 Rostock Germany
- Department LL&M University of Rostock Albert-Einstein-Str. 25 18059 Rostock Germany
- Leibniz-Institut für Katalyse an der Universität Rostock e.V. Albert-Einstein-Str. 29a 18059 Rostock Germany
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Damodaran K. Recent advances in NMR spectroscopy of ionic liquids. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2022; 129:1-27. [PMID: 35292132 DOI: 10.1016/j.pnmrs.2021.12.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 12/17/2021] [Accepted: 12/28/2021] [Indexed: 06/14/2023]
Abstract
This review presents recent developments in the application of NMR spectroscopic techniques in the study of ionic liquids. NMR has been the primary tool not only for the structural characterization of ionic liquids, but also for the study of dynamics. The presence of a host of NMR active nuclei in ionic liquids permits widespread use of multinuclear NMR experiments. Chemical shifts and multinuclear coupling constants are used routinely for the structure elucidation of ionic liquids and of products formed by their covalent interactions with other materials. Also, the availability of a multitude of NMR techniques has facilitated the study of dynamical processes in them. These include the use of NOESY to study inter-ionic interactions, pulsed-field gradient techniques for probing transport properties, and relaxation measurements to elucidate rotational dynamics. This review will focus on the application of each of these techniques to investigate ionic liquids.
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Affiliation(s)
- Krishnan Damodaran
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, United States.
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Khudozhitkov AE, Stange P, Stepanov AG, Kolokolov DI, Ludwig R. Structure, hydrogen bond dynamics and phase transition in a model ionic liquid electrolyte. Phys Chem Chem Phys 2022; 24:6064-6071. [PMID: 35212342 DOI: 10.1039/d2cp00452f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We show that solid-state NMR spectroscopy is a suitable method for characterizing the structure, hydrogen bond dynamics and phase transition behavior in protic ionic liquids (PILs). Deuteron line shape and spin relaxation time analysis provide a description of the structural and dynamical heterogeneity in the solid state of the model PIL triethyl ammonium bis(trifluoromethanesulfonyl)amide [TEA][NTf2]. Therein, we observed two deuteron quadrupole coupling constant for the ND bond of the TEA cation, indicating differently strong hydrogen bonds to the nitrogen and oxygen atoms of the NTf2 anion, as we could confirm by DFT calculations. The transition processes in the dynamically heterogeneous phase are characterized by two standard molar enthalpies and thus different stages of melting. We provide geometry, rates and energetics of the cation in the solid and liquid states of the PIL. Comparison with PILs having stronger interacting anions shows higher enthalpy change between the solid and liquid states, lower activation barriers of tumbling motion and higher amplitude of librational motion for the TEA cation in the presence of the weakly interacting anion NTf2. We provide reasonable relations between microscopic and macroscopic properties, as is relevant for any kind of application.
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Affiliation(s)
- Alexander E Khudozhitkov
- Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia. .,Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russia
| | - Peter Stange
- Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr-Lorenz-Weg 2, 18059 Rostock, Germany
| | - Alexander G Stepanov
- Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia.
| | - Daniil I Kolokolov
- Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia. .,Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russia
| | - Ralf Ludwig
- Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr-Lorenz-Weg 2, 18059 Rostock, Germany.,Leibniz-Institut für Katalyse an der Universität Rostock e.V, Albert-Einstein-Str. 29a, 18059 Rostock, Germany.
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Al-Sheakh L, Fritsch S, Appelhagen A, Villinger A, Ludwig R. Thermodynamically Stable Cationic Dimers in Carboxyl-Functionalized Ionic Liquids: The Paradoxical Case of "Anti-Electrostatic" Hydrogen Bonding. Molecules 2022; 27:molecules27020366. [PMID: 35056680 PMCID: PMC8778807 DOI: 10.3390/molecules27020366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/28/2021] [Accepted: 01/03/2022] [Indexed: 11/18/2022] Open
Abstract
We show that carboxyl-functionalized ionic liquids (ILs) form doubly hydrogen-bonded cationic dimers (c+=c+) despite the repulsive forces between ions of like charge and competing hydrogen bonds between cation and anion (c+–a−). This structural motif as known for formic acid, the archetype of double hydrogen bridges, is present in the solid state of the IL 1−(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC−CH2−py][NTf2]. By means of quantum chemical calculations, we explored different hydrogen-bonded isomers of neutral (HOOC–(CH2)n–py+)2(NTf2−)2, single-charged (HOOC–(CH2)n–py+)2(NTf2−), and double-charged (HOOC– (CH2)n−py+)2 complexes for demonstrating the paradoxical case of “anti-electrostatic” hydrogen bonding (AEHB) between ions of like charge. For the pure doubly hydrogen-bonded cationic dimers (HOOC– (CH2)n−py+)2, we report robust kinetic stability for n = 1–4. At n = 5, hydrogen bonding and dispersion fully compensate for the repulsive Coulomb forces between the cations, allowing for the quantification of the two equivalent hydrogen bonds and dispersion interaction in the order of 58.5 and 11 kJmol−1, respectively. For n = 6–8, we calculated negative free energies for temperatures below 47, 80, and 114 K, respectively. Quantum cluster equilibrium (QCE) theory predicts the equilibria between cationic monomers and dimers by considering the intermolecular interaction between the species, leading to thermodynamic stability at even higher temperatures. We rationalize the H-bond characteristics of the cationic dimers by the natural bond orbital (NBO) approach, emphasizing the strong correlation between NBO-based and spectroscopic descriptors, such as NMR chemical shifts and vibrational frequencies.
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Affiliation(s)
- Loai Al-Sheakh
- Institut für Chemie, Abteilung für Physikalische Chemie, Universität Rostock, Dr.-Lorenz-Weg 2, 18059 Rostock, Germany; (L.A.-S.); (S.F.); (A.A.)
| | - Sebastian Fritsch
- Institut für Chemie, Abteilung für Physikalische Chemie, Universität Rostock, Dr.-Lorenz-Weg 2, 18059 Rostock, Germany; (L.A.-S.); (S.F.); (A.A.)
| | - Andreas Appelhagen
- Institut für Chemie, Abteilung für Physikalische Chemie, Universität Rostock, Dr.-Lorenz-Weg 2, 18059 Rostock, Germany; (L.A.-S.); (S.F.); (A.A.)
| | - Alexander Villinger
- Institut für Chemie, Abteilung für Anorganische Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany;
| | - Ralf Ludwig
- Institut für Chemie, Abteilung für Physikalische Chemie, Universität Rostock, Dr.-Lorenz-Weg 2, 18059 Rostock, Germany; (L.A.-S.); (S.F.); (A.A.)
- Department LL&M, University of Rostock, Albert-Einstein−Str. 25, 18059 Rostock, Germany
- Leibniz−Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein−Str. 29a, 18059 Rostock, Germany
- Correspondence:
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Ivanov MY, Surovtsev NV, Fedin MV. Ionic liquid glasses: properties and applications. RUSSIAN CHEMICAL REVIEWS 2022. [DOI: 10.1070/rcr5031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Becher M, Körber T, Döß A, Hinze G, Gainaru C, Böhmer R, Vogel M, Rössler EA. Nuclear Spin Relaxation in Viscous Liquids: Relaxation Stretching of Single-Particle Probes. J Phys Chem B 2021; 125:13519-13532. [PMID: 34860530 DOI: 10.1021/acs.jpcb.1c06722] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Spin-lattice relaxation rates R1(ω,T), probed via high-field and field-cycling nuclear magnetic resonance (NMR), are used to test the validity of frequency-temperature superposition (FTS) for the reorientation dynamics in viscous liquids. For several liquids, FTS is found to apply so that master curves can be generated. The susceptibility spectra are highly similar to those obtained from depolarized light scattering (DLS) and reveal an excess wing. Where FTS works, two approaches are suggested to access the susceptibility: (i) a plot of deuteron R1(T) vs the spin-spin relaxation rate R2(T) and (ii) a plot of R1(T) vs an independently measured reference time τref(T). Using single-frequency scans, (i) allows one to extract the relaxation stretching as well as the NMR coupling constant. Surveying 26 data sets, we find Kohlrausch functions with exponents 0.39 < βK ≤ 0.67. Plots of the spin-spin relaxation rate R2─rescaled by the NMR coupling constant─as a function of temperature allow one to test how well site-specific NMR relaxations couple to a given reference process. Upon cooling of flexible molecule liquids, the site-specific dynamics is found to merge, suggesting that near Tg the molecules reorient essentially as a rigid entity. This presents a possible resolution for the much lower stretching parameters reported here at high temperatures that contrast with the ones that were reported to be universal in a recent DLS study close to Tg. Our analysis underlines that deuteron relaxation is a uniquely powerful tool to probe single-particle reorientation.
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Affiliation(s)
- M Becher
- Anorganische Chemie III and Nordbayerisches NMR Zentrum, Universität Bayreuth, 95440 Bayreuth, Germany
| | - Th Körber
- Anorganische Chemie III and Nordbayerisches NMR Zentrum, Universität Bayreuth, 95440 Bayreuth, Germany
| | - A Döß
- Department Chemie, Johannes Gutenberg-Universität, 55128 Mainz, Germany
| | - G Hinze
- Department Chemie, Johannes Gutenberg-Universität, 55128 Mainz, Germany
| | - C Gainaru
- Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund, Germany.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - R Böhmer
- Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund, Germany
| | - M Vogel
- Institut für Physik kondensierter Materie, Technische Universität Darmstadt, 64289 Darmstadt, Germany
| | - E A Rössler
- Anorganische Chemie III and Nordbayerisches NMR Zentrum, Universität Bayreuth, 95440 Bayreuth, Germany
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Philipp JK, Fritsch S, Ludwig R. Cyclic Octamer of Hydroxyl-functionalized Cations with Net Charge Q=+8e Kinetically Stabilized by a 'Molecular Island' of Cooperative Hydrogen Bonds. Chemphyschem 2020; 21:2411-2416. [PMID: 32845043 PMCID: PMC7702028 DOI: 10.1002/cphc.202000681] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 08/20/2020] [Indexed: 11/07/2022]
Abstract
Cyclic octamers are well-known structural motifs in chemistry, biology and physics. These include covalently bound cyclic octameric sulphur, cylic octa-alkanes, cyclo-octameric peptides as well as hydrogen-bonded ring clusters of alcohols. In this work, we show that even calculated cyclic octamers of hydroxy-functionalized pyridinium cations with a net charge Q=+8e are kinetically stable. Eight positively charged cations are kept together by hydrogen bonding despite the strong Coulomb repulsive forces. Sufficiently long hydroxy-octyl chains prevent "Coulomb explosion" by increasing the distance between the positive charges at the pyridinium rings, reducing the Coulomb repulsion and thus strengthen hydrogen bonds between the OH groups. The eightfold positively charged cyclic octamer shows spectroscopic properties similar to those obtained for hydrogen-bonded neutral cyclic octamers of methanol. Thus, the area of the hydrogen bonded OH ring represents a 'molecular island' within an overall cationic environment. Although not observable, the spectroscopic properties and the correlated NBO parameters of the calculated cationic octamer support the detection of smaller cationic clusters in ionic liquids, which we observed despite the competition with ion pairs wherein attractive Coulomb forces enhance hydrogen bonding between cation and anion.
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Affiliation(s)
- Jule Kristin Philipp
- Universität RostockInstitut für ChemieAbteilung Physikalische und Theoretische ChemieDr.-Lorenz-Weg 218059RostockGermany
| | - Sebastian Fritsch
- Universität RostockInstitut für ChemieAbteilung Physikalische und Theoretische ChemieDr.-Lorenz-Weg 218059RostockGermany
| | - Ralf Ludwig
- Universität RostockInstitut für ChemieAbteilung Physikalische und Theoretische ChemieDr.-Lorenz-Weg 218059RostockGermany
- Universität RostockDepartment LL&MAlbert-Einstein-Str. 2518059RostockGermany
- Leibniz-Institut für Katalyse an der Universität Rostock e.V.Albert-Einstein-Str. 29a18059RostockGermany
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Philipp JK, Ludwig R. Clusters of Hydroxyl-Functionalized Cations Stabilized by Cooperative Hydrogen Bonds: The Role of Polarizability and Alkyl Chain Length. Molecules 2020; 25:molecules25214972. [PMID: 33121087 PMCID: PMC7662246 DOI: 10.3390/molecules25214972] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 10/22/2020] [Accepted: 10/24/2020] [Indexed: 01/08/2023] Open
Abstract
We explore quantum chemical calculations for studying clusters of hydroxyl-functionalized cations kinetically stabilized by hydrogen bonding despite strongly repulsive electrostatic forces. In a comprehensive study, we calculate clusters of ammonium, piperidinium, pyrrolidinium, imidazolium, pyridinium, and imidazolium cations, which are prominent constituents of ionic liquids. All cations are decorated with hydroxy-alkyl chains allowing H-bond formation between ions of like charge. The cluster topologies comprise linear and cyclic clusters up to the size of hexamers. The ring structures exhibit cooperative hydrogen bonds opposing the repulsive Coulomb forces and leading to kinetic stability of the clusters. We discuss the importance of hydrogen bonding and dispersion forces for the stability of the differently sized clusters. We find the largest clusters when hydrogen bonding is maximized in cyclic topologies and dispersion interaction is properly taken into account. The kinetic stability of the clusters with short-chained cations is studied for the different types of cations ranging from hard to polarizable or exhibiting additional functional groups such as the acidic C(2)-H position in the imidazolium-based cation. Increasing the alkyl chain length, the cation effect diminishes and the kinetic stability is exclusively governed by the alkyl chain tether increasing the distance between the positively charged rings of the cations. With adding the counterion tetrafluoroborate (BF4−) to the cationic clusters, the binding energies immediately switch from strongly positive to strongly negative. In the neutral clusters, the OH functional groups of the cations can interact either with other cations or with the anions. The hexamer cluster with the cyclic H-bond motive and “released” anions is almost as stable as the hexamer built by H-bonded ion pairs exclusively, which is in accord with recent IR spectra of similar ionic liquids detecting both types of hydrogen bonding. For the cationic and neutral clusters, we discuss geometric and spectroscopic properties as sensitive probes of opposite- and like-charge interaction. Finally, we show that NMR proton chemical shifts and deuteron quadrupole coupling constants can be related to each other, allowing to predict properties which are not easily accessible by experiment.
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Affiliation(s)
- Jule K. Philipp
- Institut für Chemie, Abteilung Physikalische und Theoretische Chemie, Universität Rostock, 18059 Rostock, Germany;
| | - Ralf Ludwig
- Institut für Chemie, Abteilung Physikalische und Theoretische Chemie, Universität Rostock, 18059 Rostock, Germany;
- Department Life, Light & Matter, Universität Rostock, Albert-Einstein-Str. 25, 18059 Rostock, Germany
- Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany
- Correspondence: ; Tel.: +49-381-498-6517
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