Geminal Dicationic Ionic Liquids Research Articles

Geminal Dicationic Ionic Liquids (GDILs) and Their Adsorption on Graphene Nanoflakes.

In this work, the configuration and stability of 15 geminal dicationic ionic liquids (GDILs) and their adsorption mechanism on the graphene nanoflake (GNF) are investigated using the density functional theory (DFT) method. We find that the interactions of dications ([DAm]+, [DIm]+, [DImDm]+, [DPy]+, and [DPyrr]+)) are stabilized near the anions ([BF4]-, [PF6]-, and [Tf2N]-) in the most stable configurations of GDILs through electrostatic interactions, van der Waals (vdW) interactions, and hydrogen bonding (H-bonding). Our calculations show that the adsorption of the GDILs on the GNF is consistent with the charge transfer and occurs via X···π (X = N, O, F), C-H···π, and π···π noncovalent interactions, leading to a decrease in the strength of the intermolecular interactions between the dications and anions in the GDILs. The thermochemistry calculations reveal that the formation of GDIL@GNF complexes is an exothermic and favorable reaction. The adsorption energy (Eads) calculations show that the highest Eads values for the interaction of GDILs containing [BF4]-, [PF6]-, and [Tf2N]- anions with the GNF are observed for the [DPy][BF4]@GNF (-23.56 kcal/mol), [DPy][PF6]@GNF (-29.29 kcal/mol), and [DPyrr][Tf2N]@GNF (-24.74 kcal/mol) complexes, respectively. Our results show that the adsorption of the GDILs on the GNF leads to the decrease of the chemical potential (μ), chemical hardness (η), and HOMO-LUMO energy gap (Eg) values and an increase in the electrophilicity index (ω) value of the GNF. In addition, the effect of GDIL adsorption on the UV-vis absorption spectrum was studied at the TD-M06-2X/cc-pVDZ level of theory. We find that the adsorption of GDILs results in minimal change in the shape of the main absorption peak (at λ = 363 nm) in the GNF spectrum and only shifts it to higher wavelengths. On the other hand, a new peak appears in the GNF spectrum upon adsorption of [DPy][Y] (Y = [BF4]-, [PF6]-, and [Tf2N]-) due to the relatively strong π···π interactions between the [DPy]+ dication and GNF. Finally, the transition density matrix (TDM) heat maps show that electron transfers related to the excitation states in the GDIL@GNF complexes occur mainly through π(C=C) → π*(C=C) transitions in the GNF and the transitions from [DPy]+ dication to the GNF.

Geminal Dicationic Ionic Liquid-Based Freestanding Ion Membrane for High-Safety Lithium Batteries.

A freestanding ion membrane with high ionic conductivity, electrochemical compatibility, satisfactory strength, and safety is a goal pursued for advanced energy storage. Geminal dicationic ionic liquids (GDILs) are expected to be designed and synthesized as a basic building block for the target ionic conductors. Herein, we fabricated a GDIL-based flexible ion conductive material, which appears and behaves as a freestanding film, an ion membrane actually, denoted as iMembrane. The iMembrane presented high thermal stability, broad electrochemical stability, and capable ionic conductivity. Stable lithium-ion intercalation/de-intercalation can be achieved at the iMembrane/graphite interface without co-intercalation of imidazole rings, which is attributed to the specific anion-derived solid electrolyte interphase. Moreover, iMembrane is well compatible with the lithium metal anode and LiFePO4 cathode. The soft-packed batteries assembled with iMembrane were punctured with a nail without any fire or smoke. Hence, as an ionic membrane in nonprotonic, iMembrane is promising to enhance safety and energy density of lithium batteries.

Synthesis and application of geminal dicationic ionic liquids and poly (ionic liquids) combined imidazolium and pyridinium cations as demulsifiers for petroleum crude oil saline water emulsions

New geminal dicationic ionic liquids, ILs, containing both imidazolium and pyridinium cations were synthesized to apply as effective demulsifiers for stable sea water-in-heavy petroleum crude oil emulsions. In this respect, vinyl imidazolium and 4- amino-4-pyridyl diethoxylate (APE) or 4-pyridyl tetradecanamide were quaternized either with 1,4-dibromobutane or 1,12-dibromododecane to produce ILs monomers. Their vinyl group was polymerized via solution radical polymerization to produce geminal poly (ionic liquids), PILs, and their chemical structures were identified by nuclear magnetic resonance. The thermal stability and thermal characteristics of the prepared geminal dicationic imidazolium and pyridinium cations indicate that all prepared compounds behave as ILs and PILs having lower melting temperature below 100 °C and lower glass transition temperatures below 0 °C. The surface activity, micellization or aggregation, and adsorption at air/seawater or seawater/petroleum crude oil interfaces were investigated from surface and interfacial tension measurements. The interactions of the prepared ILs and PILs with asphaltenes were evaluated from particle sizes and zeta potentials. The demulsification of stable W/O emulsions at temperature of 60 °C using different concentrations of the prepared ILs and PILs confirm that the demulsification was carried out at lower injection dose (from 100 to 250 ppm) and shorter demulsification time (from 40 to 240 min).

Electronic structure, vibrational spectra and 1H NMR chemical shifts of the ion pair composites within imidazolium functionalized geminal dicationic ionic liquids from density functional theory

Electronic structure, vibrational and 1H NMR spectra of geminal dication based ionic liquids composed of the functionalized imidazolium cation and bis(trifluoromethanesulfonyl)imide (Tf2N‾) anion have been obtained through the M06-2x based density functional theory. Underlying C–H⋯O, C–H⋯F, anion-π and van der Waals interactions in such complexes are unveiled through natural bond orbital and noncovalent reduced density gradient analyses. Calculated infrared spectra have shown that dication-anion complexes are accompanied by frequency downshifts of the hydrogen bonded SO3 and CF3 vibrations, whereas the uncoupled and intense C–H stretching emerges with its shift in the opposite direction (blue shift or frequency up shift) compared to free Tf2N‾ anion. Further the C-H vibrational frequency increases steadily with diminutive kinetic energy density component in the quantum theory of atoms in molecules (QTAIM) analyses. Besides, the large down-field signal of the (reactive) methine proton on the imidazolium in 1H NMR spectra correlates well with the electron density at the bond critical point in QTAIM analyses.

Investigation of PEG-6000 bridged $$\hbox {-N-SO}_{3}\hbox {H}$$ -N-SO 3 H functionalized geminal dicationic ionic liquids for catalytic conversion of fructose to 5-hydroxymethylfurfural

Eight new members of two series of PEG-6000-bridged geminal dicationic ionic liquids based on diphenylammonium/imidazolium cation were synthesized by the change of four anions $$\hbox {CF}_{3}\hbox {COO}^{-}$$ , $$\hbox {CCl}_{3}\hbox {COO}^{-}$$ , $$\hbox {AcO}^{-}$$ and $$\hbox {HSO}_{4}^{-}$$ . They were investigated as reusable acidic catalysts for dehydration of fructose to 5-hydroxymethylfurfural in polar aprotic solvent. The characterizations of dicationic ionic liquids were done using $${}^{1}\hbox {H NMR}$$ , $${}^{13}\hbox {C NMR}$$ , IR and TGA analyses. Irrespective of Hammett acidity strength of the eight ILs, they displayed single peak selectivity for the 5-hydroxymethyl furfural intermediate in HPLC analysis. Two series of N-sulfonic acid functionalized PEG-6000 bridged geminal dicationic diphenylammonium/imidazolium ionic liquids were developed in pair with $$\hbox {CF}_{3}\hbox {COO}^{-}$$ , $$\hbox {CCl}_{3}\hbox {COO}^{-}$$ , $$\hbox {AcO}^{-}$$ and $$\hbox {HSO}_{4}^{-}$$ anions. Single peak selectivity of 5-hydroxymethylfurfural in HPLCs was observed from dehydration of fructose in polar aprotic solvent using these acidic ionic liquid catalysts.

Design, Synthesis, and Analysis of Thermophysical Properties for Imidazolium-Based Geminal Dicationic Ionic Liquids

To enhance the thermal stability of ionic liquids (ILs) and increase the latent heat, the effect of amount of hydrogen bonds for geminal dicationic ionic liquids (DILs) was investigated and compared to that of monocationic analogues. A series of geminal dicationic ionic liquids with alkyl chain or electronegativity functional groups in the imidazolium were synthesized. Thermal stability was determined by TGA; melting point, heat of fusion, and heat capacity were investigated by DSC for synthetic DILs. The effect of molecular structure on the heat of fusion was examined by changes alkyl side-chain, linkage chain, C2–H of imidazole ring, and functional groups. Hydrogen bonding in DILs was studied, in the case of C2(eim)2(Br)2, by single-crystal X-ray diffraction. The thermal analysis results indicate that functionalized geminal dicationic ionic liquids show excellent thermal stability. The decomposition temperatures of geminal dicationic ionic liquids can be up to 603.74 K, and the latent heat can reach 159...

Molecular dynamics simulation of geminal dicationic ionic liquids [Cn(mim)2][NTf2]2 - structural and dynamical properties.

In this work, the structural and dynamical properties of two imidazolium-based geminal dicationic ionic liquids (GDILs), i.e. [Cn(mim)2][NTf2]2 with n = 3 and 5, have been studied to obtain a fundamental understanding of the molecular basis of the macroscopic and microscopic properties of the bulk liquid phase. To achieve this purpose, molecular dynamics (MD) simulation, density functional theory (DFT) and atoms in molecule (AIM) methods were used. Interaction energies, charge transfers and hydrogen bonds between the cation and anions of each studied GDIL were investigated by DFT calculations and also AIM. The mean square displacement (MSD), self-diffusion coefficient, and transference number of the cation and anions, and also the density, viscosity and electrical conductivity of the studied GDILs, were computed at 333.15 K and at 1 atm. The simulated values were in good agreement with the experimental data. The effect of linkage alkyl chain length on the thermodynamic, transport and structural properties of these GDILs has been investigated. The structural features of these GDILs were characterized by calculating the partial site-site radial distribution functions (RDFs) and spatial distribution functions (SDFs). The heterogeneity order parameter (HOP) has been used to describe the spatial structures of these GDILs and the distribution of the angles formed between two cation heads and the middle carbon atom of the linkage alkyl chain was analyzed in these ILs. To investigate the temporal heterogeneity of the studied GDILs, the deviation of the self-part of the van Hove correlation function, Gs(r[combining right harpoon above],t), from the Gaussian distribution of particle displacement and also the second-order non-Gaussian parameter, α2(t), were used. Since, the transport and interfacial properties and ionic characteristics of these GDILs were studied experimentally in our previous studies as a function of linkage chain length and temperature, in this work, we try to give a better perspective of the structure and dynamics of these systems at a molecular level.

Examination of Selectivities of Thermally Stable Geminal Dicationic Ionic Liquids by Structural Modification

Dicationic ionic liquids (ILs) are widely used as gas chromatography (GC) stationary phases as they show higher thermal stabilities, variety of polarities, and unique selectivities towards certain compounds. An important aspect contributing to them is that they show multiple solvation interactions compared to the traditional GC stationary phases. Dicationic ILs are considered as combination of three structural moieties: (1) cationic head groups; (2) a linkage chain; and (3) the counter anions. Modifications in these structural moieties can alter the chromatographic properties of IL stationary phases. In this study, a series of nine thermally stable IL stationary phases were synthesized by the combination of five different cations, two different linkage chains, and two different anions. Different test mixtures composed of a variety of compounds having different functional groups and polarities were analyzed on these columns. A comparison of the separation patterns of these different compounds on nine different IL columns provided some insights about the effects of structural modifications on the selectivities and polarities of dicationic ILs.

A mechanistic study of geminal dicationic ionic liquids as mobile phase additives for improving the separation performance of high-performance liquid chromatography.

Due to the acidity and strong polarity of auxinic herbicides, separation of these compounds in food and environmental samples is a great challenge. In this study, 12 geminal dicationic ionic liquids (GDILs) were synthesized and used as mobile phase additives to separate six auxinic herbicides. The effects of the kind of dication, the length of linkage chain, the kind of anion, the concentration of GDILs, and the pH of mobile phase for the separation were investigated in detail. Compared with [C4MIm][BF4], GDILs ([C8(MIm)2][BF4]2) showed higher resolution, better peak shape, and lower retention factor. The separation performance of additives was in the order of [C8(MIm)2][BF4]2>[C8(MPy)2][BF4]2, [(C4)2MPiz][BF4]2, [C8(MMo)2][BF4]2, [C4MIm][BF4], [C8(MPid)2][BF4]2>[C8(HBOc)2][BF4]2>TBAB. GDILs showed the best separation under the following conditions: cation: imidazolium; length of linkage chain: 8; anion: BF4-; mobile phase pH: 3; concentration: 5mmolL-1. The separation mechanism of GDILs may mainly be due to their symmetric structure and the abundance of positive charge sites which could help GDILs shield the residual silanol and interact with analytes more efficiently to improve the peak shapes, resolution, and retention. In addition, the GDILs in the mobile phase and anions adsorbed on the stationary phase also greatly affected the separation. GDILs used as mobile phase additives to separate auxinic herbicides showed high efficiency separation and low damage to HPLC columns, and the developed chromatographic method had excellent linearity, accuracy, precision, and repeatability. The application and mechanism study of GDILs in HPLC would be instructive to determine and separate acid herbicides in food and environmental samples. Graphical abstract As HPLC mobile phase additives, GDILs show high separation performance due to their unique symmetric structures.

The effects of temperature and alkyl chain length on the density and surface tension of the imidazolium-based geminal dicationic ionic liquids

Surface tensions and densities of three imidazolium-based geminal dicationic ionic liquids (GDILs) with the bis(trifluoromethylsulfonyl)imide, [NTf2]−, as a common anion, have been measured at ambient pressure at different temperatures in the range from 296.00 to 353.15K. The surface thermodynamic functions such as surface entropy and surface enthalpy were derived from the temperature dependence of surface tension which indicated the surface ordering in these GDILs. As well as the parachor, the critical temperatures of these systems have been estimated using the Guggenheim and Eotvos correlations. In each case, the results of GDILs have been compared with the results of corresponding traditional monocationic ILs (MILs). Also, the relations between the surface tension and density and also surface tension and viscosity data have been demonstrated and discussed.

Synthesis of Thermally Stable Geminal Dicationic Ionic Liquids and Related Ionic Compounds: An Examination of Physicochemical Properties by Structural Modification

Geminal dicationic ionic liquids (ILs) often display higher thermal stabilities, viscosities, and densities compared to traditional monocationic ILs. Also, dicationic ILs have advantages in terms of tuning of their physicochemical properties by different structural modifications. They can be considered as a combination of three structural moieties: (1) cationic head groups, (2) an alkane linker chain, and (3) the associated anions. Two types of each imidazolium, pyrrolidinium, and phosphonium cations were joined by different alkane linkages (C6, C9, and C12) to develop 18 different dications. These dications were paired with two different anions (NTf2– and PFOS–) to synthesize 36 different dicationic ILs. The effect of variations in the structural moieties of these related ILs on their physicochemical properties, including melting points, densities, viscosities, solubilities, and thermal stabilities, were evaluated. ILs synthesized in this study displayed TGA thermal stabilities in the range 330–467 °C. A...

Unveiling the complex network of interactions in Ionic Liquids: a combined EXAFS and Molecular Dynamics approach

The structural properties of geminal dicationic ionic liquids ([Cn (mim)2]Br2)/water mixtures have been investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy and Molecular Dynamics (MD) simulations. This synergic approach allowed us to assess the reliability of the MD results and to provide accurate structural information about the first coordination shell of the Br- ion. We found that the local environment around the anion changes as a function of the water concentration, while it is the same independently from the length of the bridge-alkyl chain. Moreover, as regards the long-range structural organization, no tail-tail aggregation occurs with increasing alkyl chain length.

Structural properties of geminal dicationic ionic liquid/water mixtures: a theoretical and experimental insight.

The structural behavior of geminal dicationic ionic liquid 1,n-bis[3-methylimidazolium-1-yl] alkane bromide ([Cn(mim)2]Br2)/water mixtures has been studied using extended X-ray absorption fine structure (EXAFS) spectroscopy in combination with molecular dynamics (MD) simulations. The properties of the mixtures are investigated as a function of both water concentration and alkyl-bridge chain length. The very good agreement between the EXAFS experimental data and the theoretical curves calculated from the MD structural results has proven the validity of the theoretical framework used for all of the investigated systems. In all the solutions the water molecules are preferentially coordinated with the Br(-) ion, even if a complex network of interactions among dications, anions and water molecules takes place. The local molecular arrangement around the bromide ion is found to change with increasing water content, as more and more water molecules are accomodated in the Br(-) first coordination shell. Moreover, with the decrease of the alkyl-bridge chain length, the interactions between dications and anions increase, with Br(-) forming a bridge between the two imidazolium rings of the same dication. On the other hand, in [Cn(mim)2]Br2/water mixtures with long alkyl-bridge chains peculiar internal arrangements of the dications are found, leading to different structural features of geminal dicationic ionic liquids as compared to their monocationic counterparts.

Study of surface-bonded dicationic ionic liquids as stationary phases for hydrophilic interaction chromatography

In the present study, several geminal dicationic ionic liquids based on 1,4-bis(3-allylimidazolium)butane and 1,8-bis(3-allylimidazolium)octane in combination with different anions bromide and bis(trifluoromethanesulphonyl)imide were prepared and then bonded to the surface of 3-mercaptopropyl modified silica materials through the “thiol-ene” click chemistry as stationary phases for hydrophilic interaction chromatography (HILIC). Compared with their monocationic analogues, the dicationic ionic liquids stationary phases presented effective retention and good selectivity for typical hydrophilic compounds under HILIC mode with the column efficiency as high as 130,000 plates/m. Moreover, the influence of different alkyl chain spacer between dications and combined anions on the retention behavior and selectivity of the dicationic ionic liquids stationary phases under HILIC mode was displayed. The results indicated that the longer linkage chain would decrease the hydrophilicity and retention on the dicationic ionic liquid stationary phase, and while differently combined anions had no difference due to the exchangeability under the common HILIC mobile phase with buffer salt. Finally, the retention mechanism was investigated by evaluating the effect of chromatographic factors on retention, including the water content in the mobile phase, the mobile phase pH and buffer salt concentration. The results showed that the dicationic ionic liquids stationary phases presented a mixed-mode retention behavior with HILIC mechanism and anion exchange.

Cation-size-controlled assembly of the Ni(Ac)₂-1,4-H₂NDC system: geminal dicationic ionothermal syntheses, crystal structures and magnetic properties.

Geminal dicationic ionic liquids with different alkyl spacer lengths regularly tune four MOF structures of two structure types in the Ni(Ac)2-1,4-H2NDC system, which in turn bring about the magnetic properties divided into antiferromagnetic and ferromagnetic couplings consistent with the structures.

Synthesis, characterization and the antimicrobial activity of new eco-friendly ionic liquids

A green microwave-assisted procedure for the preparation of a series of 24 new 1-alkyl-3-ethylimidazolium ionic liquids with different functional groups in the alkyl chain is described. Moreover, the synthesis of a variety of ten new geminal dicationic ionic liquids is reported. Their structures were characterized by FT-IR, 1H NMR, 13C NMR, 11B, 19F, 31P, and mass spectrometry. Several ionic liquids were selected for antimicrobial activity studies, yielding very interesting and promising results.

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

AbstractIn this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C6(mim)]+_X−, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C6(mim)2X2], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl− and Br− anions prefer to locate almost in the plane of the imidazolium ring whereas the I− anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl− and Br− anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.

New supramolecular ionic networks based on citric acid and geminal dicationic ionic liquids

A new family of supramolecular ionic networks was synthesized by a straightforward method using citric acid and germinal dicationic ionic liquids. The networks were formed by the ionic boding of multi carboxylate and cationic molecules. The resulting networks are solid soft material at room temperature, which exhibited a thermoreversible transition, becoming a viscoelastic liquid at high temperatures. Thus, each supramolecular ionic network was characterized by an elastic modulus, Ge, and a network-liquid transition temperature, Tnl. The glass transition temperature, Tg, of the systems was evaluated by differential scanning calorimetry (DSC) measurements, which, however, were not able to detect the Tnl. Considering the effect of the employed dicationic ionic liquids, the three characteristic parameters of the networks, Ge, Tnl and Tg, followed the same trend, as they increased following the sequence: citrate-1,3-propanedipyridinium > citrate-1,3-propanedimethylimidazolium > citrate/1,3-propanedimethylpyrrolidinium and citrate/1,3-propanedibenzylimidazolium. The nature of the dication and its substituents determined the basic parameters of the elastic network, Ge and Tnl. The observed effect of the chemical structure on Tg was assumed to be due to a reduction of the free volume as Ge augments.

Molecular Dynamic Simulation of Dicationic Ionic Liquids: Effects of Anions and Alkyl Chain Length on Liquid Structure and Diffusion

Structures and dynamics of nine geminal dicationic ionic liquids (DILs) Cn(mim)2X2, where n = 3, 6, and 9 and X = PF6(-), BF4(-), and Br(-), were studied by molecular dynamic simulations (J. Phys. Chem.B2004, 108, 2038-2047). A force field with a minor modification for C3(mim)2 × 2 was adopted for the simulations. Densities, detailed microscopic structures, mean-square displacements (MSD), and self-diffusivities for various ion pairs from MD simulations have been presented. The calculated densities for C9(mim)2X2 (X = Br(-) and BF4(-)) agreed well with the experimental values. The calculated RDFs show that anions are well organized around the imidazolium rings. The calculated RDFs indicate that, unlike the mono cationic ILs, the anions and cations in DILs distribute homogeneously. Enthalpies of vaporization were calculated and correlated with the structural features of DILs. The local structure of C9(mim)2X2 (X = Br, PF6) was examined by the spatial distribution function (SDF). The calculated SDFs show that similar trends were found by other groups for mono cationic ionic liquids (ILs). The highest probability densities are located around the imidazolium ring hydrogens. The calculated diffusion coefficients show that the ion diffusivities are 1 order of magnitude smaller than that of the mono cationic ionic liquids. The effects of alkyl chain length and anion type on the diffusion coefficient were also studied. The dynamics of the imidazolium rings and the alkyl chain in different time scales have also discussed. The calculated transference numbers show that the anions have the major role in carrying the electric current in a DIL.

Geometrical and electronic structures of the dication and ion pair in the geminal dicationic ionic liquid 1,3-bis[3-methylimidazolium-yl]propane bromide

Geminal dicationic ionic liquids (ILs), a new category of IL family, have been developed recently and found to possess unique properties compared to conventional monocationic ILs. To establish a basis for understanding their novel properties, we studied the geometrical and electronic structures of the dication ([(mim)C 3(mim)] 2+) and the ion pair ([(mim)C 3(mim)] 2+-2Br −) in the geminal dicationic IL 1,3-bis[3-methylimidazolium-yl]propane bromide by performing density functional theory calculations. The geometrical structures and relative stabilities for the dication and the ion pair are discussed, and their electronic properties are analyzed in detail. The intrinsic interaction between the dication and Br anions in the most stable conformer was investigated by performing the natural bond orbital analyses. Results for the dication and the ion pair are compared with those of the corresponding monocation ([C 4mim] +) and ion pair ([C 4mim] +-Br −). 1H NMR spectroscopy for the most stable ion pair has been calculated and the general trend is found to be in fairly agreement with the experimental data.