Hydrogen Bonding in 1-Butyl- and 1-Ethyl-3-methylimidazolium Chloride Ionic Liquids (original) (raw)
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Hydrogen Bonding in 1-Butyl- and 1-Ethyl-3-methylimidazolium Chloride Ionic Liquids B
The Journal of Physical Chemistry, 2012
A detailed investigation of hydrogen bonding in the pure ionic liquids [C 4 C 1 im]Cl and [C 2 C 1 im]Cl has been carried out using primarily molecular dynamics techniques. Analyses of the individual atom−atom pair radial distribution functions, and in particular those for C•••Cl − , have revealed that hydrogen bonding to the first methylene or methyl units of the substituent groups is important. Multiple geometric criteria for defining a hydrogen bond have been applied, and in particular the choice of the cutoff angle has been carefully examined. The interpretation of hydrogen bonding within these ionic liquids is highly angle dependent, and justification is provided for why it may be appropriate to employ a wider angle criteria than the 30°used for water or alcohol systems. The different types of hydrogen bond formed are characterized, and "top" conformations where the Cl anion resides above (or below) the imidazolium ring are investigated. The number of hydrogen bonds undertaken by each hydrogen atom (and the chloride anion) is quantified, and the propensity to form zero, one, or two hydrogen bonds is established. The effects of an increase in temperature on the static hydrogen bonding are also briefly examined.
The Journal of Physical Chemistry B, 2013
Hydrogen bonding in ionic liquids based on the 1-(2′hydroxylethyl)-3-methylimidazolium cation ([C 2 OHmim] + ) and various anions ([A] − ) of differing H-bond acceptor strength, viz. hexafluorophosphate [PF 6 ] − , tetrafluoroborate [BF 4 ] − , bis-(trifluoromethanesulfonimide) [Tf 2 N] − , trifluoromethylsulfonate [OTf] − , and trifluoroacetate [TFA] − , was studied by a range of spectroscopic and computational techniques and, in the case of [C 2 OHmim][PF 6 ], by single crystal X-ray diffraction. The first quantitative estimates of the energy (E HB ) and the enthalpy (−ΔH HB ) of H-bonds in bulk ILs were obtained from a theoretical analysis of the solid-state electron-density map of crystalline [C 2 OHmim][PF 6 ] and an analysis of the IR spectra in crystal and liquid samples. E HB for OH···[PF 6 ] − H-bonds amounts to ∼3.4−3.8 kcal·mol −1 , whereas weaker H-bonds (2.8−3.1 kcal·mol −1 ) are formed between aromatic C2H group of imidazolium ring and the [PF 6 ] − anion. The enthalpy of the OH···[A] − H-bonds follows the order: [PF 6 ] (2.4 kcal·mol −1 ) < [BF 4 ] (3.3 kcal·mol −1 ) < [Tf 2 N] (3.4 kcal·mol −1 ) < [OTf] (4.7 kcal·mol −1 l) < [TFA] (6.2 kcal·mol −1 ). The formation of aggregates of self-associated [C 2 OHmim] + cations is present in liquid [C 2 OHmim][PF 6 ], [C 2 OHmim][BF 4 ], and [C 2 OHmim][Tf 2 N]
The Journal of Physical Chemistry B, 2011
The virtual laboratory allows for computer experiments that are not accessible via real experiments. In this work, three previously obtained charge sets were employed to study the influence of hydrogen bonding on imidazolium-based ionic liquids in molecular dynamics simulations. One set provides diffusion coefficients in agreement with the experiment and is therefore a good model for real-world systems. Comparison with the other sets indicates hydrogen bonding to influence structure and dynamics differently. Furthermore, in one case the total charge was increased and in another decreased by 0.1 e. Both the most acidic proton as well as the corresponding carbon atom were artificially set to zero, sequentially and simultaneously. In the final setup a negative charge was placed on the proton in order to introduce a barrier for the anion to contact the cation via this most acidic hydrogen atom. The following observations were made: changing the hydrogen bonding ability strongly influences the structure while the dynamic properties, such as diffusion and viscosity, are only weakly changed. However, the introduction of larger alterations (stronger hydrogen bonding and antihydrogen bonding) also strongly influences the diffusion coefficients. The dynamics of the hydrogen bond, ion pairing, and the ion cage are all affected by the level of hydrogen bonding. A change in total charges predominantly influences transport properties rather than structure. For ion cage dynamics with respect to transport porperties, we find a good correlation and a weak or no correlation for the ion pair or the hydrogen bond dynamics, respectively. Nevertheless, the hydrogen bond does influence ion cage dynamics. Therefore, we confirm that ionic liquids rather consist of loosely interacting counterions than of discrete ion pairs. Hydrogen bonding affects the properties only in a secondary or indirect manner.
1H, 13C NMR and DFT Study of Hydrogen Bonding in Imidazolium-based Ionic Liquids
Acta chimica Slovenica, 2011
The ionic liquid 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], the neat material, and also dissolved (~0.01 mole fraction) in various dielectric media (acetonitrile, benzene, chloroform, dichloromethane, methanol, 2-butanol and H2O) was studied using 1H and 13C NMR spectroscopy. The most important interaction in this compound is considered to be the Br-...H-C2+ hydrogen bond, which is formed between the anions and cations. The obtained results show that dielectric medium influence mostly the behavior of the Br-...H-C2+ bridge proton. The changes observed in 1H and 13C NMR spectra of [C10mim][Br] with increasing solvents polarity and temperature can be explained applying the model of the lengthening of the H2...Br- bond with the accompanying thickening of the solvation shell of bromine anion and C2-H bond contraction. The short-range order effects related to the configuration of neighboring dipoles of solvent molecules are more important for the solvation ability of small anions...
International Journal of Molecular Sciences, 2021
Knowledge of all the intermolecular forces occurring in ionic liquids (ILs) is essential to master their properties. Aiming at investigating the weaker hydrogen bonding in aprotic liquids, the present work combined computational study and far-infrared spectroscopy on four imidazolium-based ILs with different anions. The DFT calculations of the ionic couples, using the ωB97X-D functional and considering both the empirical dispersion corrections and the presence of a polar solvent, show that, for all samples, the lowest energy configurations of the ion pair present H atoms, directly bound to C atoms of the cation and close to O atoms of the anion, capable of creating moderate to weak hydrogen bonding with anions. For the liquids containing anions of higher bonding ability, the absorption curves generated from the calculated vibrational frequencies and intensities show absorption bands between 100 and 125 cm−1 corresponding to the stretching of the hydrogen bond. These indications are ...
Vibrational spectroscopy (Raman) and quantum chemical theory (DFT) are employed to investigate the effect of aromatic, aliphatic H-bonding and weak interactions on conformational changes in 1-isopropyl-3-methylimidazolium (i-C 3 mim +) based ILs. In previous report (J. Phys. Chem. A, 2008, 112, 7543–7550), it is reported that two conformations (Asym and Sym conformer) are remained in equilibrium for 1-isopropyl-3-methylimidazoliumBr/I (i-C 3 mimBr/I) ILs and Asym conformer is more stable and predominating in population over Sym conformer (Asym:Sym = 7:3). But in our case of 2,3-dimethyl (1-isopropyl)-imidazoliumPF 6 (Mi-C 3 mimPF 6) IL, Sym conformer is more stable than Asym conformer and relative population of Sym conformer is higher than Asym conformer (Asym:Sym = 2:8) in liquid state. The combining effect of C2-Me and PF 6 anion on Sym and Asym conformer has been discussed with help of H-bonding interactions between cation and anion by experimental and DFT studies.
Hydrogen bonding in ionic liquids probed by linear and nonlinear vibrational spectroscopy
New Journal of Physics, 2012
Three imidazolium-based ionic liquids of the type [C n mim][NTf 2 ] with different alkyl chain lengths (n = 1, 2 and 8) at the first position of the imidazolium ring were studied applying infrared, linear Raman and multiplex coherent anti-Stokes Raman scattering spectroscopy. The focus has been on the CH-stretching region of the imidazolium ring, which is supposed to carry information about a possible hydrogen bonding network in the ionic liquid. The measurements are compared with calculations of the corresponding anharmonic vibrational spectra for a cluster of [C 2 mim][NTf 2 ] consisting of four ion pairs. The results support the hypothesis of weak hydrogen bonding involving the C(4)-H and C(5)-H groups and somewhat stronger hydrogen bonds of the C(2)-H groups.
arXiv (Cornell University), 2022
Ionic liquids (ILs) feature a tailorable and wide range of structural, chemical and electronic properties that make this class of materials suitable to a broad variety of forefront applications in next-generation electronics. Yet, their intrinsic complexity call for special attention and experimental probes have still limitations in unraveling the interactions occurring both in the bulk IL and at the interface with the solid substrates used to build the devices. This works provides an atomistic insight into these fundamental interactions by molecular modeling to complement the information still not accessible to experiments. In particular, we shed some light on the nature of the chemical bonding, structure, charge distribution and dipolar properties of a series of alkyl-imidazolium-based ILs by a synergy of classical and first-principles molecular dynamics simulations. Special emphasis is given to the crucial issue of the hydrogen bond network formation ability depending either on the nature of the anion or on the length of the alkyl chain of the cation. The hydrogen bond strength is a fundamental indicator of the cohesive and ordering features of the ILs and, in this respect, might be exploited to foster a different behaviour of the IL used a bulk medium or when used in electronic devices.
Angewandte Chemie, 2019
We present deuteron quadrupole coupling constants (DQCC) for hydroxyl-functionalized ionic liquids (ILs) in the crystalline or glassy states characterizing two types of hydrogen bonding:T he regular Coulomb-enhanced hydrogen bonds between cation and anion (c-a), and the unusual hydrogen bonds between cation and cation (c-c), which are present despite repulsive Coulomb forces.W em easure these sensitive probes of hydrogen bonding by means of solid-state NMR spectroscopy. The DQCCs of (c-a) ion pairs and (c-c) Hbonds are compared to those of salt bridges in supramolecular complexes and those present in molecular liquids.A tl ow temperatures,t he (c-c) species successfully compete with the (c-a) ion pairs and dominate the cluster populations.Equilibrium constants obtained from molecular-dynamics (MD) simulations show vantH off behavior with small transition enthalpies between the differently H-bonded species.W eshow that cationic-cluster formation prevents these ILs from crystallizing.W ith cooling,t he (c-c) hydrogen bonds persist, resulting in supercooling and glass formation.