Structural Organization and Supramolecular Interactions of the Task

Article pubs.acs.org/JPCC

Structural Organization and Supramolecular Interactions of the Task-Specific Ionic Liquid 1‑Methyl-3-carboxymethylimidazolium Chloride: Solid, Solution, and Gas Phase Structures Alberto A. R. Mota,†,# Claudia C. Gatto,†,# Giovanna Machado,‡,# Heibbe C. B. de Oliveira,†,# Maíra Fasciotti,§,#,⊥ Otavio Bianchi,∥,# Marcos N. Eberlin,§,# and Brenno A. D. Neto*,†,# †

Laboratory of Medicinal and Technological Chemistry, Chemistry Institute, University of Brasília (UnB), Campus Universitario Darcy Ribeiro, CEP 70904-970, P.O. Box 4478, Brasilia−DF, Brazil ‡ Center for Strategic Technologies of the North East (CETENE), Recife, Brazil § ThoMSon Mass Spectrometry Laboratory, University of Campinas-UNICAMP, 13083-970 Campinas-SP, Brazil ∥ Programa de Pos-Graduacao em Ciência e Engenharia de Materiais (PGMAT), Universidade de Caxias do sul, 95070-560, Caxias do Sul-RS, Brazil S Supporting Information *

ABSTRACT: Using a set of different techniques, which included single crystal X-ray, NMR, UV− vis, conductivity measurements, SAXS (small angle X-rays), ESI-MS(/MS) (electrospray (tandem) mass spectrometry), and theoretical calculations, an ample study of the structural organization and supramolecular interaction of the task-specific ionic liquid 1-methyl-3carboxymethylimidazolium chloride (named MAI.Cl) was conducted. All techniques allowed for comprehensive investigation in the solid state, solution, and gas-phase behavior of MAI.Cl. Most relevant interactions are demonstrated showing the importance of hydrogen bonding to supramolecular organization of MAI.Cl in different states and its tendency to aggregate in aqueous solutions.

■

commonly used as reaction media,41−43 organocatalysts,44−46 ligands for complexes and organometallic catalysts,47 or stabilizing agents for metal nanoparticles,48 their supramolecular cation−anion interactions (neat and in solution), (self-) aggregate formation and three-dimensional arrangement will therefore directly affect the undergoing process. The cooperative cation−anion pairing and/or aggregation formation effects play therefore fundamental roles on the reaction course with great influence over yields and selectivities.49−51 For instance, we have recently demonstrated the loss of catalytic activity upon increased catalyst concentration due to aggregation of an iron complex bearing a TSIL ligand with imidazolium tags.52 Hydrogen bonds have proved to play a crucial role for imidazolium-based ILs.53−55 There is a consensus on the dominance of Coulombic interactions and some advocates that H-bonds are much less relevant as alleged.56−58 As for IL, similar influence should also be expected for TSILs and indeed, H-bonds have been shown, for instance, to play an essential role in the organization of an TSIL (imidazolium-based) bearing an amide functionalization.36 An important class of TSILs is formed by those bearing carboxylic acid(s) group(s).59 For example, it has been recently showed that the presence of a carboxylic group in a TSIL allows

INTRODUCTION Today, ionic liquids (IL) are widespread via many scientific and technological areas, with emphasis in material sciences.1−3 ILs have assumed paramount importance for the chemical industry, as already reviewed elsewhere.4 Imidazolium-based ILs5 comprise an important and attractive IL class.6 A new class of functionalized derivatives7 have also been developed and termed task-specific ionic liquids (TSILs).8,9 As for ILs in general, the use of the imidazolium cation as the ionic tag for TSILs and their applications have recently experienced great expansion.10−12 The physicochemical properties of imidazolium derivatives are intimately associated with their capacity of forming wellorganized three-dimensional networks displaying organized directionality.13 Despite all advances made in the comprehension of the properties and structural organization of ILs,14 fine details are only now starting to emerge. Vast literature is available on the structural organization,15−17 supramolecular interactions,18−20 and (self-) aggregation behavior21−23 of imidazolium-based ILs, but such details for TSILs have remained much less explored.24−39 It is now common sense that the chemical constitution of the IL determines the nature of the cation and anion interactions.40 Structure has therefore a direct effect on the IL threedimensional organization and aggregation behavior. This relationship sets an imperative requirement for the comprehension of the supramolecular interactions of TSILs. Since TSILs are © 2014 American Chemical Society

Received: June 26, 2014 Revised: July 10, 2014 Published: July 15, 2014 17878

dx.doi.org/10.1021/jp506363h | J. Phys. Chem. C 2014, 118, 17878−17889

The Journal of Physical Chemistry C

Article

micelle formation with considerably lower concentration compared to that with no functionalization.24 Oxidative desulfurization of fuels showed to be considerably more efficient when using −COOH-containing TSILs.60 The 1-methyl-3-carboxymethylimidazolium chloride (MAI.Cl) investigated here (Figure 1), for instance, was successfully used as an efficient

Table 1. X-ray Diffraction Data Collection and Refinement Parameters for MAI.Cl compound chemical formula M (g mol−1) crystal system space group unit cell a (Å) b (Å) c (Å) V (Å3) Z Dc (g cm−3) index ranges

Figure 1. Structure of 1-methyl-3-carboxymethylimidazolium chloride (MAI.Cl) investigated in this work.

metal nanoparticle stabilizer.61 MAI.Cl was also applied as a recyclable catalyst for the three-component Mannich reaction.62 We also have shown that MAI.Cl could be efficiently used as the ligand for the in situ generation of a palladiumorganometallic catalysts to promote the Heck and Suzuki reactions.63 More recently, we used cation MAI as a chargetagged precursor to investigate the formation and role of carbenes in protic solvents,64 as the catalyst for the Biginelli multicomponent reaction,65 as ligand for lanthanide-based watersoluble complexes66 applied for bioimaging experiments, and as the charge-tagged reagent to investigate the Ugi multicomponent reaction (four components).67 Due to the high importance of a better knowledge of the supramolecular assembly of TSILs, our interest in ILs chemistry68−70 and our interest in the development and application of TSILs,52,63,71 we described herein a systematic study performed on the supramolecular interactions of MAI.Cl in solution, condensed, and gas-phase, focusing on the importance of hydrogen bonds for the physicochemical properties of this important TSIL.

absorption coefficient (mm−1) absorption correction max/min transmission measured reflections independent reflections (Rint) refined parameters R1 (F)/wR2 (F2) (I > 2σ(I)) GooF largest diff. peak and hole (eÅ−3) deposit number CCDC

MAI.Cl C6H9ClN2O2 176.60 orthorhombic Pca21 13.425(2) 6.375(1) 9.709(1) 830.9(2) 4 1.412 −19 ≤ h ≤ 17 −5 ≤ k ≤ 9 −12 ≤ l ≤ 13 0.412 multiscan 0.9599/0.7959 5339 2299/0.0141 103 0.0275/0.0710 1.071 0.155 and −0.144 1002177

■

RESULTS AND DISCUSSION X-ray Analysis. The molecular structure of MAI.Cl has been investigated by single-crystal X-ray diffraction crystallographic analysis. Table 1 summarizes the crystal and structure refinement data. Interestingly, the molecules were found to pack in stacks of cations MAI and anions (Cl−) with an extended network connected by H-bonds (Figure 2). The imidazolium cations are also found organized through π-stacking interactions (3.08 Å, the distance between two imidazolium moieties) commonly seen in aromatic derivatives.72 The observed π-stacking of MAI.Cl is similar to nonfunctionalized ILs,73,74 but with some significant differences. Single-crystal X-ray analysis (Figure 3) shows that one cation is surrounded by four anions and that anions are surrounded also by four cations (Figure 3). Typically for nonfunctionalized ILs, three anions surround a cation and vice versa.15 Table 2 summarizes the close contacts distances and angles noted for a single cation and single anion (see Figure 3). No close contact is observed, however, between Cl− and hydrogens at C4 and C5, which has been noted for nonfunctionalized ILs.75 Following the criteria adopted by T. Steiner,76 for H-bonds the cutoff limits of 3.2 Å for distance and above 110° for angles (conservative option) were used. Hence, Entries 1−4 and 7−8 (from Table 1) were considered as H-bonds. Entry 9 (Table 2) with a bond distance slightly above 3.2 Å (upper limit) was not considered as H-bond. At least six possible H-bonds were therefore demonstrated for

Figure 2. View of the crystal structure of MAI.Cl along the crystallographic y-axis. Hydrogen atoms have been omitted for clarity, except for −COOH. Note the ionic channels formation in the molecules pack.

MAI.Cl in the solid state for its network of stacked anions and the cations. Interestingly, at least two of such H-bonds are noted between two different MAI cations (two ion pairs), whereas the others are noted in the same ion pair. NMR Analysis. The well-known proton spin−lattice relaxation times (T1)77 have been used as the NMR technique applied for the cation−anion investigation of MAI.Cl. It is already established that the chemical environment and changes in the molecular dynamics have a direct effect on the T1 measurement. For instance, T1 has been used to determine the critical aggregation concentrations (CAC) of some ammonium surfactants.78 All experiments described herein were performed at 20 °C in a NMR tube containing a sealed capillary tube charged with benzene-d6 (external reference to set the scale at 7.16 ppm for 1H and 128.4 ppm for 13C) and initial concentration of 110 mmol/L. Figure S1 (in the Supporting Information) shows the 1H and 13C NMR spectra of MAI.Cl. T1 experiments were performed in pure D2O, D2O/CD3OD (1:1 v/v) and D2O/CD3CN (1:1 v/v) so as to evaluate the 17879



Article

Figure 3. Highlighted interactions observed for MAI.Cl. View of the close contacts of the anion (Cl−) and the cation (MAI). (A) Local structure and close contacts around a single anion. (B) Local structure and close contacts around a single cation. Note that one anion is surrounded by four cations and the cation surrounded by four anions.

water content and the capability of forming and affecting Hbonds with MAI.Cl may therefore be analyzed by NMR, as already reviewed.82 For some, water is responsible to induce a better aggregation of ILs due to solvent-structure enforced ion pairing, which is essentially driven by non-Coulombic shortrange interactions (e.g., H-bonds).83−86 Figure 4 clearly shows a transition-phase for the CAC in water around ≈ 0.5 mol/L. Above this concentration, dipole−dipole relaxation are favored and the observed T1 is lower. In the presence of protic solvent (CD3OD), the aggregation behavior is deeply affected and competitive H-bonds of the alcohol are shifting the CAC. The aggregation is indeed more difficult and most probably the formed aggregates are smaller than those observed in water (as will be discussed in due course by SAXS analysis). The polar and aprotic solvent (CD3CN) also has an influence on the CAC but clearly not as pronounced as that observed for CD3OD. Interestingly, chemical-shift dependence of the imidazolium hydrogens and of the aliphatic hydrogens could be observed in the 1H NMR spectra (Figure S2). This behavior is again coherent with the observation that aggregate formation is preferred in water and that solvent separated ion pairs occurs when methanol or acetonitrile are added in the aqueous solution, in full accordance with similar observations for nonfunctionalized imidazolium ILs.74 UV−vis Analysis. It is known that UV−vis spectra are sensitive to the microenvironment changes taking place in π-conjugated systems solutions (e.g., imidazolium derivatives). Therefore, it is possible to depict via UV−vis information on the nature and nanostructure assembles of imidazolium derivatives87 and for other substances88 in different solutions. UV−vis experiments in water, methanol, acetonitrile, methanol− water and acetonitrile−water mixtures at several concentrations of MAI.Cl were therefore conducted (Figures S3−6). Note that absorption bands above 220 nm are attributed to the imidazolium ring. The second derivatives (Figures S4 and S5) allows determination of the λmax of absorption and the shifts suffered through solvent effect. With these data in hands, the effect of aggregates formation over the absorbance and wavenumber of absorption (Figure 5) could be evaluated. A limit for the linear behavior of the Lambert−Beer law is noted and above those limits, a deviation is noted, indicating the formation of supramolecular aggregates of MAI.Cl. An easily notable change (increase) in molar extinction coefficients was therefore found, as also observed for

Table 2. Distance of Close Contacts and Angles for the Anion and for the Cation of MAI.Cl entry 1 2 3 4 5a 6a 7 8 9 a

distance (Å) and atoms 2.166 2.911 2.766 2.840 3.325 3.849 2.535 2.711 3.217

(H2A···Cl1) (H2···Cl1) (H7A···Cl1) (H7B···Cl1) (H2···Cl1) (H7A···Cl1) (H6A···O1) (H2···O1) (H5B···O2)

angle (°) and atoms 169.34 (O2-H2A···Cl1) 138.53 (C2-H2···Cl1) 138.08 (C7-H7A···Cl1) 128.95 (C7-H7B···Cl1) 82.88 (C2-H2···Cl1) 99.59 (C7-H7A···Cl1) 152.45 (C6-H6A···O1) 138.19 (C2-H2···O1) 138.60 (C7-H5B···O2)

Interaction with a cation in other ion pair.

intermolecular interactions and to probe the importance of the H-bond for the supramolecular aggregate formation. Table 3 summarizes results under optimized conditions. Table 3. Relaxation time (s) for MAI.Cl (110 mmol/L) in different solvents.

hydrogen C2-H C4-H and C5-H C6H3 C7H2

T1 (error) in T1 (error) in D2O D2O/CD3OD (1:1 v/v)

T1 (error) in D2O/CD3CN (1:1 v/v)

5.843 (±0.271) 6.254 (±0.224)

4.145 (±0.107) 4.691 (±0.100)

5.981 (±0.116) 6.457 (±0.205)

1.671 (±0.046) 2.699 (±0.105)

1.861 (±0.065) 1.092 (±0.022)

1.681 (±0.030) 2.571 (±0.037)

Clearly, there is a solvent effect over T1 measurement. Hence, at this point we conclude that methanol has a direct influence on the aggregation state of MAI.Cl. To corroborate such hypothesis, T1 measurements were performed by varying the concentration for the three solvent systems (Figure 4). Water is known to directly effects the 3D supramolecular structures of imidazolium-based ILs. Water−cation and water− anion interactions alter the primary structure of the pure IL by changing its primary supramolecular interactions16 (cation− anion) and this effect can be monitored by NMR.79−81 The 17880



Article

Figure 4. T1 values for the hydrogens of MAI.Cl under different concentrations. Each point refers to an independent experiment. From top to bottom: D2O, D2O/CD3OD (1:1 v/v) and D2O/CD3CN (1:1 v/v).

nonfunctionalized ILs.87 The effects observed herein likely are a consequence of supramolecular aggregates formation and different solvents proportions at a fixed concentration had no effect over aggregates (Figure S6). Conductivity Analysis. Conductivity has been used as a powerful tool to study IL behavior (aggregate states) in solution because the conductivity measurement is directly associated with the free ions in solution.89 Conductivity has already been successfully used to evaluate the aggregation behavior of aqueous solutions of ILs.85 The measured conductivities have been converted to molar conductivities and plotted (Figure 6) according to Kohlrausch’s empirical law (that is, following the equation Λm = Λ0 − k·C−1/2, where C is the concentration) and in different solvents and mixtures (water, methanol, acetonitrile, methanol−water, and acetonitrile−water mixtures). Two distinct breaks in the Kohlrausch plots are noted, which indicate two regimes of differing aggregate nature, as previously shown for nonfunctionalized ILs.85 Table 4 reports the concentrations at which the break points occur. In general, the addition of methanol clearly facilitate the dissociation of the ion pairs and the breaking of the larger aggregates. For higher methanol concentrations, the second regime of aggregation (β) was not observed. For MeCNcontaining solutions, both the first (α) and the second (β) breaks could be easily determined. The values for the β regime in the MeCN-containing solutions at low concentrations were however by far lower when compared with methanolcontaining solutions. The results again indicate the methanol effect toward ion pairs dissociations and aggregates breaking. In all, the results indicate that the competitive interactions (especially H-bonds) between the MAI cation and methanol is by far more pronounced than those observed with MeCN. SAXS Analyses. Compared to X-ray diffraction, SAXS has a modest resolution (1−3 nm) that is not sufficient to reveal the atomic structure of materials. SAXS is, however, a wellestablished technique for studying the morphology, shape (spherical, cylindrical, platelet, cubic, etc.), and size distribution of a multiphase sample as well as for obtaining information of

nanostrucutural parameters, such as orientation, degree of orientation, mean distance between particles, and large molecules. Structural information on inhomogeneities of the electron density in the samples are also available. SAXS was therefore applied to help understanding the local organization of cations and anions in MAI.Cl, especially because ILs should show a complex local organization with self-aggregating polar and nonpolar domains of the nanometer size.5 This knowledge is very important, in particular, because the resulting ion−ion association will impact on the ionic transport properties. More detailed information about the interaction of ILs with different solvents may be therefore obtained from SAXS analyses. Figure 7 shows data analysis for saturated aqueous and methanolic solutions of MAI.Cl. Figure 7 depicts the correlation (γ(r)) and interface distribution (G(r)) functions of MAI.Cl dispersed in water and methanol solvents. Using the two phase model,90−92 it was possible to obtain the length of the aggregates. In water it is noted an increase to high r values of the position of maxima in the correlation function corresponding to an enhancement of the most probable distance between the two centers of gravity (TSIL aggregates) represented as long period (L). On the other hand, the distance, Lm, represented as the position of the first minimum in the correlation function, which is interpreted as the most probable distance between the centers of gravity of the TSIL aggregates and their adjacent solvent regions. When the aggregate of MAI.Cl is found dispersed in the solvent, a one-dimensional ideal lattice is formed and the values of L and Lm coincide. If this super lattice is not ideal, however, the position of the maximum, L, and minimum, Lm, in the correlation function may be slightly shifted. This shift is clearly indicated by the intensity values of the γ(r) function via the presence of semiordered phases for MAI.Cl in water, which is more organized than the methanolic solution. Again, this result indicates that MAI.Cl is mainly found aggregated in aqueous solutions, likely because the water molecules preferentially interact with its anions domain through an H-bonding network, whereas the oxygen atoms of water interact with the acidic 17881



Article

Figure 5. Absorbance vs concentration and wavenumber vs concentration at different concentration of MAI.Cl in water, methanol, acetonitrile, methanol−water and acetonitrile−water mixtures.

Electrospray (Tandem) Mass Spectrometry Analyses: ESI-MS(/MS). Mass spectrometry has proved to be an outstanding tool to investigate ILs and TSILs, as recently reviewed.98 We have already described important properties of ILs/TSILs using ESI-MS(/MS).67,99−101 We therefore used ESI-MS(/MS) to investigate the gas-phase chemistry and association behavior of MAI.Cl, initiating our investigation with the ESI(+)-MS (Figure 8) of an aqueous solution of MAI.Cl (50 μM). Interestingly, not only the free MAI cation of m/z 141 was fished out from the solution by ESI(+)-MS, but also two of its supramolecular aggregates of m/z 281 and 421. These unique supramolecular ions were therefore characterized through collision-induced dissociation (Figure 9). Scheme 1 summarizes the solution chemistry of MAI.Cl revealed by ESI(+)-MS(/MS) and the gaseous species that were transferred and found to represent long-lived gaseous species. Considering that methanol displayed the most pronounced effect toward aggregate dissociation, we also monitored a 50 μM solution of a methanol:water mixture (1:1 v/v) via ESI(+)-MS (Figure 10). In the methanol/water solution, indeed, the supramolecular cation of m/z 421 was nearly suppressed corroborating again

hydrogens of MAI.Cl. This system has, therefore, an excess of the mixing enthalpy, as already noted for the interactions of ILs and water.93 Methanol interactions proved, however, to be weaker than those involving water molecules, in accordance with previous results for imidazolium-based ILs.94 Applying the G(r) function to the experimental data, the first maximum can be estimated as disorder solvent-phase represented by Lm. The model considers that MAI.Cl (semiordered phase) are surrounded by solvent (semiordered phase). This result was obtained from the subtraction of L from Lm. The value obtained represent the distance between the two scattering centers without solvent returning the aggregates molecular lengths of 1.28 and 0.90 nm for water and methanol solutions, respectively. Note that this result also demonstrates that MAI.Cl is mainly aggregate in aqueous solutions. Considering the molecular diameter of water of 0.25 nm95 and 0.42 nm96 for methanol, it is possible to determine the number of molecules neighboring each molecule of MAI.Cl. For the aqueous solution, up to four molecules were found surrounding MAI.Cl and two for methanol. This difference between water and methanol is most likely due to the superior ability of water to solvate the chloride anion97 and therefore the distance between aggregates neighbors is increased. 17882



Article

Figure 6. (Left) C−1/2 vs Λm of MAI.Cl at different H2O/MeOH mixtures in several concentrations. (Right) C−1/2 vs Λm of MAI.Cl at different H2O/MeCN mixtures in several concentrations.

Table 4. Relaxation Time (s) for MAI.Cl (110 mmol/L) in Different Solvents

Scheme 1. Supramolecular Cations (from Aggregation) Observed in the ESI(+)-MS(/MS) Experiments

concentration (mmol/L) solvent and proportion mixture

α

β

H2O/CH3OH 0:1 H2O/CH3OH 3:1 H2O/CH3OH 1:1 H2O/CH3OH 1:3 H2O/CH3OH 0:1 H2O/CH3CN 0:1 H2O/CH3CN 3:1 H2O/CH3CN 1:1 H2O/CH3CN 1:3 H2O/CH3CN 0:1

2.54−3.38 2.53−3.38 3.38−5.05 3.38−5.05 3.38−5.05 2.51−3.35 3.35−5.00 2.51−3.35 3.35−5.00 5.00−6.65

11.64−13.26 19.63−22.76

11.52−13.13 13.13−14.72 16.31−19.44 16.91−19.44 19.44−22.54

Table 5. Relative Interaction Energies (Internal Energies, ΔE) for the Cation−Anion Interaction at Different Positions at MP2/6-311+g* Level of Theory relative energies (kcal mol−1) ΔE internal ΔE orbitalar ΔE steric

C2-H2···Cl1 C7-H7B···Cl1 0.00 0.00 0.00

5.71 −0.30 6.01

O2-H2A···Cl1

C7-H7A···Cl1

20.93 −2.20 23.13

0.19 −0.80 0.99

MAI.Cl. Its structure was fully optimize and the best superimposition between the X-ray and the calculated structure obtained using the basis set function 6−311+g* and MP2 as the method (see Table S1 for all tested conditions and RMSD values) was selected for the forthcoming theoretical calculations and analyses. After the level of calculations was determined, the crystallographic coordinates (from a single crystal X-ray analysis) were taken frozen during all calculations. Hybrid methods (at different levels of theory) have also been evaluated (Table S2), but calculations at MP2/6−311+g* displayed good accuracy when compared to hybrid methods. The energetics associated with the deconvolution followed Morokuma’s recommendations102 for energy decomposition analysis, and the total energy (internal energy) was the sum of

Figure 7. SAXS analyses for MAI.Cl in methanol and water (saturated solutions).

the methanol effect in promoting supramolecular aggregate dissociation. The supramolecular ion of m/z 281 was also considerably less abundant than in pure aqueous solution. Theoretical Calculations. Theoretical calculations have also been performed to achieve a better understanding of the nature of the contributions for the aggregate formation of 17883



Article

Figure 8. ESI(+)-MS of an aqueous solution of MAI.Cl (50 μM).

Figure 9. ESI(+)-MS/MS of the supramolecular cations of m/z 421 (top) and m/z 281 (bottom).

Figure 11 shows the relative energies of ion-pairing and the considered interactions between Cl− and the different positions of the MAI cation (especially for Coulombic contributions), as observed by X-ray analysis (Figure 3 and Table 2). Figure 11 shows that O2-H2A···Cl1 has the most pronounced orbitalar contribution, whereas C2-H2···Cl1 is the most pronounced interaction associated with steric interaction (Coulombic ionpairing), in accordance with the data from X-ray analysis. The other

the steric (related to electrostatic interactions) and orbitalar contributions, according to eq 1. ΔE = ΔEsteric + ΔEorb

(1)

where ΔE is the internal energy (total energy of the contribution), ΔEsteric is the steric energy (associated with electrostatic attraction and Pauling repulsion’s energies), and ΔEorb is the orbitalar contribution. Table 5 shows the relative energies values. 17884



Article

Figure 10. ESI(+)-MS of methanol/water (1:1 v/v) solution of MAI.Cl (50 μM).

Table 6. Electron Density (ρ), Laplacian ρ(r), and Ellipticity (ε) Calculated for MAI.Cl bond path

ρ(r)

Laplacian of ρ(r)

ellipticity (ε)

Cl1···C2 Cl1···H2 Cl1···H7A Cl1···H2A Cl1···H7B Cl1···H5

0.009 0.007 0.009 0.026 0.008 0.005

+0.0253 +0.0213 +0.0299 +0.0890 +0.0268 +0.0161

0.15 0.07 0.12 0.01 0.24 0.09

point” (BCP), that is, the point with the minimal ρ value along the bond path (Figure 13). The charge density ρ(r) characterizes each point in space and allows to deduce the type of interaction, that is, H-bond, van der Waals, and so on. The gradient of ρ(r), the Laplacian function of ρ(r), and the matrix of the second derivatives of ρ(r) (Hessian matrix) also characterize the system, as reviewed elsewhere.103−106 The Laplacian of the charge density at the bond critical point found between 0.024 and 0.131(9) (atomic units) may be associated with H-bonds, as previously determined.107,108 As Figure 13 shows, O2-H2A···Cl1 interaction is the strongest H-bond (0.089 au), whereas the interaction associated with C2-H2···Cl1 contribution (0.021 au) is in the lower limit to be considered a H-bond (Table 6). The charge density values for H-bonds are in the range of 0.002−0.035 (atomic units).108 Despite Table 6 indicating values within this range, other criteria must also be satisfied. The ellipticity values ε < 0.1 are associated with well-defined H-bonds.108 The analysis of all parameters calculated using QTAIM indicates at least three strong H-bond, that is, O2-H2A···Cl1, C2-H2···Cl1, and C5-H5···Cl1

Figure 11. Relative energies (internal energy) of cation−anion interactions for the chloride anion and the MAI cation at different positions based on the X-ray structure (inset). Note the relative energy of 0.00 kcal mol−1 has the most pronounced Coulombic interaction, whereas the relative energy of 20.93 has the most pronounced orbitalar contribution.

two interactions are energetically close and have therefore similar contributions. Using the natural bonding orbital (NBO) analyses it was possible a better understanding on the contribution of each of these interactions related to orbitalar contribution (Figure 12). NBO analyses are again found in accordance with the conclusion that the most strong orbitalar interaction is that of O2-H2A···Cl1. Interesting, the C2-H2···Cl1 interaction has a negligible contribution to the system stabilization, whereas the other two interactions had similar contribution. These results are again similar to those obtained from the X-ray data (Figure 3 and Table 2). Finally, Baders quantum theory of “atoms in molecules” (QTAIM) was used to evaluate the so-called “bond critical

Figure 12. Interaction energies (values in kcal mol−1) from natural bonding orbital (NBO) analyses (left) and orbital interaction (HOMO and LUMO) for the O2-H2A···Cl1 interaction (calculated for this ion pair). 17885



Article

Figure 13. Results from quantum theory of “atoms in molecules” applied for the task-specific ionic liquid MAI.Cl. (A) Critical points (show as green spots; see between the represented bond paths and interactions) and the calculated values for the Laplacian function of ρ(r) in their bond critical point. (B, D) Gradient vectors fields of charge densities associated with the representative topologies of the calculated electron density function for the atoms found in the imidazolium ring (B) and for those in the side chain (D). Note that (B) and (D) also show the atoms domains and their individual contributions in the molecule. (C) Three-dimensional view for the whole structure of MAI.Cl of the calculated Laplacian function of ρ(r).

corrections for all of the calculated structures. This material is available free of charge via the Internet at http://pubs.acs.org.

Calculations indicate therefore that electrostatic interactions play major roles for the ion-pairing in the structure of MAI.Cl. H-bonds, however, also play crucial roles, especially for the directionality and for the additional structural stabilization, therefore, in accordance with recent conclusions for some TSILs39 and with some recent organizational theory for ILs/TSILs.5

■

*E-mail: [email protected].

■

Author Contributions

CONCLUSIONS The condensed, solution, and gas-phase behavior of the TSIL 1-methyl-3-carboxymethylimidazolium chloride (MAI.Cl) has been investigated. X-ray analysis revealed the strong cation− anion interactions and some H-bond contributions. NMR, UV−vis, conductivity, and SAXS analyses revealed the preferential aggregation of MAI.Cl in aqueous solution in a perfect parallel to the observations previously described for nonfunctionalized ILs. ESI-MS(/MS) was able to fish out from solutions supramolecular aggregates of MAI.Cl and their abundances, as compared to the MAI cation, and the results were in accordance with the observation that the TSIL MAI.Cl was mainly aggregated in water rather than in organic protic solvents. Theoretical calculations showed main MAI.Cl interactions and how important their contributions are for its supramolecular organization. These data could be used as the basis for future works aiming at a better comprehension of the organization and aggregation behavior of TSILs, eventually aiding rational design of ILs/TSILs with specific physical and chemical properties.

■

AUTHOR INFORMATION

Corresponding Author

#

All authors contributed equally to this work.

Present Address ⊥

(M. F.) Institute of Metrology - Inmetro - 25250-020 Duque de Caxias, Rio de Janeiro (RJ), Brazil

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work has been partially supported by CAPES, CNPq, FINEP-MCT, FINATEC, FAPESP, FAPDF, INCT-Catalysis, DPP-UnB, and ANP-PETROBRAS. B.A.D.N. thanks INCTCatalysis and CNPq. LNLS is greatly acknowledged for the use of its facilities. All founding agencies are acknowledged for partial financial support. All the authors are in debt to Dr. Davi A. C. Ferreira for insightful suggestions.

■

REFERENCES

(1) Hallett, J. P.; Welton, T. Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2. Chem. Rev. 2011, 111, 3508− 3576. (2) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Ionic Liquid (Molten Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102, 3667− 3691.

ASSOCIATED CONTENT

S Supporting Information *

Experimental details, NMR spectra, UV−vis and second derivatives, tables, figures, Cartesian coordinates, energies, and 17886



Article

alized Imidazolium Ionic Liquids. J. Braz. Chem. Soc. 2008, 19, 426− 433. (26) Cho, C. W.; Jungnickel, C.; Stolte, S.; Preiss, U.; Arning, J.; Ranke, J.; Krossing, I.; Thoming, J. Determination of LFER Descriptors of 30 Cations of Ionic Liquids Progress in Understanding Their Molecular Interaction Potentials. ChemPhysChem 2012, 13, 780−787. (27) Twu, P.; Zhao, Q. C.; Pitner, W. R.; Acree, W. E.; Baker, G. A.; Anderson, J. L. Evaluating the Solvation Properties of Functionalized Ionic Liquids with Varied Cation/Anion Composition Using the Solvation Parameter Model. J. Chromatogr., Part A 2011, 1218, 5311− 5318. (28) Luo, S. C.; Sun, S. W.; Deorukhkar, A. R.; Lu, J. T.; Bhattacharyya, A.; Lin, I. J. B. Ionic Liquids and Ionic Liquid Crystals of Vinyl Functionalized Imidazolium Salts. J. Mater. Chem. 2011, 21, 1866−1873. (29) Liu, X. M.; Song, Z. X.; Wang, H. J. Density Functional Theory Study on the −SO3H Functionalized Acidic Ionic Liquids. Struct. Chem. 2009, 20, 509−515. (30) Gutowski, K. E.; Maginn, E. J. Amine-Functionalized TaskSpecific Ionic Liquids: A Mechanistic Explanation for the Dramatic Increase in Viscosity upon Complexation with CO2 from Molecular Simulation. J. Am. Chem. Soc. 2008, 130, 14690−14704. (31) Yu, G. R.; Zhang, S. J.; Zhou, G. H.; Liu, X. M.; Chen, X. C. Structure, Interaction and Property of Amino-Functionalized Imidazolium ILs by Molecular Dynamics Simulation and Ab Initio Calculation. AIChE J. 2007, 53, 3210−3221. (32) Paul, A.; Samanta, A. Solute Rotation and Solvation Dynamics in an Alcohol-Functionalized Room Temperature Ionic Liquid. J. Phys. Chem. B 2007, 111, 4724−4731. (33) Zhang, Q. H.; Li, Z. P.; Zhang, J.; Zhang, S. G.; Zhu, L. Y.; Yang, J.; Zhang, X. P.; Deng, Y. Q. Physicochemical Properties of NitrileFunctionalized Ionic Liquids. J. Phys. Chem. B 2007, 111, 2864−2872. (34) Saha, S.; Hamaguchi, H. O. Effect of Water on the Molecular Structure and Arrangement of Nitrile-Functionalized Ionic Liquids. J. Phys. Chem. B 2006, 110, 2777−2781. (35) Fei, Z. F.; Zhao, D. B.; Geldbach, T. J.; Scopelliti, R.; Dyson, P. J. Structure of Nitrile-Functionalized Alkyltrifluoroborate Salts. Eur. J. Inorg. Chem. 2005, 860−865. (36) Lee, K. M.; Chang, H. C.; Jiang, J. C.; Lu, L. C.; Hsiao, C. J.; Lee, Y. T.; Lin, S. H.; Lin, I. J. B. Probing C-H···X Hydrogen Bonds in Amide-Functionalized Imidazolium Salts Under High Pressure. J. Chem. Phys. 2004, 120, 8645−8650. (37) Stancik, C. M.; Lavoie, A. R.; Schutz, J.; Achurra, P. A.; Lindner, P.; Gast, A. P.; Waymouth, R. M. Micelles of ImidazoliumFunctionalized Polystyrene Diblock Copolymers Investigated with Neutron and Light Scattering. Langmuir 2004, 20, 596−605. (38) Allen, J. J.; Schneider, Y.; Kail, B. W.; Luebke, D. R.; Nulwala, H.; Damodaran, K. Nuclear Spin Relaxation and Molecular Interactions of a Novel Triazolium-Based Ionic Liquid. J. Phys. Chem. B 2013, 117, 3877−3883. (39) Katsyuba, S. A.; Vener, M. V.; Zvereva, E. E.; Fei, Z. F.; Scopelliti, R.; Laurenczy, G.; Yan, N.; Paunescu, E.; Dyson, P. J. How Strong Is Hydrogen Bonding in Ionic Liquids? Combined X-ray Crystallographic, Infrared/Raman Spectroscopic, and Density Functional Theory Study. J. Phys. Chem. B 2013, 117, 9094−9105. (40) Zhao, W.; Leroy, F.; Heggen, B.; Zahn, S.; Kirchner, B.; Balasubramanian, S.; Muller-Plathe, F. Are There Stable Ion-Pairs in Room-Temperature Ionic Liquids? Molecular Dynamics Simulations of 1-n-Butyl-3-methylimidazolium Hexafluorophosphate. J. Am. Chem. Soc. 2009, 131, 15825−15833. (41) Wong, W. L.; Wong, K. Y. Recent development in functionalized ionic liquids as reaction media and promoters. Can. J. Chem. 2012, 90, 1−16. (42) Zhao, H.; Song, Z. Y.; Olubajo, O.; Cowins, J. V. New EtherFunctionalized Ionic Liquids for Lipase-Catalyzed Synthesis of Biodiesel. Appl. Biochem. Biotechnol. 2010, 162, 13−23. (43) Liu, Y.; Wang, S. S.; Liu, W.; Wan, Q. X.; Wu, H. H.; Gao, G. H. Transition-Metal Catalyzed Carbon−Carbon Couplings Mediated

(3) Welton, T. Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071−2083. (4) Plechkova, N. V.; Seddon, K. R. Applications of Ionic Liquids in the Chemical Industry. Chem. Soc. Rev. 2008, 37, 123−150. (5) Dupont, J. From Molten Salts to Ionic Liquids: A “Nano” Journey. Acc. Chem. Res. 2011, 44, 1223−1231. (6) Neto, B. A. D.; Spencer, J. The Impressive Chemistry, Applications and Features of Ionic Liquids: Properties, Catalysis and Catalysts and Trends. J. Braz. Chem. Soc. 2012, 23, 987−1007. (7) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Mayton, R.; Sheff, S.; Wierzbicki, A.; Davis, J. H.; Rogers, R. D. Task-Specific Ionic Liquids for the Extraction of Metal Ions From Aqueous Solutions. Chem. Commun. 2001, 135−136. (8) Sebesta, R.; Kmentova, I.; Toma, S. Catalysts with Ionic Tag and Their Use in Ionic Liquids. Green Chem. 2008, 10, 484−496. (9) Lombardo, M.; Trombini, C. Ionic Tags in Catalyst Optimization: Beyond Catalyst Recycling. ChemCatChem 2010, 2, 135−145. (10) Lee, S. G. Functionalized Imidazolium Salts for Task-Specific Ionic Liquids and Their Applications. Chem. Commun. 2006, 1049− 1063. (11) Luska, K. L.; Moores, A. Functionalized Ionic Liquids for the Synthesis of Metal Nanoparticles and their Application in Catalysis. ChemCatChem 2012, 4, 1534−1546. (12) Kolbeck, C.; Killian, M.; Maier, F.; Paape, N.; Wasserscheid, P.; Steinruck, H. P. Surface Characterization of Functionalized Imidazolium-Based Ionic Liquids. Langmuir 2008, 24, 9500−9507. (13) Dupont, J.; Scholten, J. D. On the Structural and Surface Properties of Transition-Metal Nanoparticles in Ionic Liquids. Chem. Soc. Rev. 2010, 39, 1780−1804. (14) Weingaertner, H. Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies. Angew. Chem., Int. Ed. 2008, 47, 654−670. (15) Dupont, J. On the Solid, Liquid and Solution Structural Organization of Imidazolium Ionic Liquids. J. Braz. Chem. Soc. 2004, 15, 341−350. (16) Mele, A.; Tran, C. D.; Lacerda, S. H. D. The Structure of a Room-Temperature Ionic Liquid with and without Trace Amounts of Water: The Role of C-H···O and C-H···F Interactions in 1-n-Butyl-3methylimidazolium Tetrafluoroborate. Angew. Chem., Int. Ed. 2003, 42, 4364−4366. (17) D’Anna, F.; Ferrante, F.; Noto, R. Geminal Ionic Liquids: A Combined Approach to Investigate Their Three-Dimensional Organisation. Chem.Eur. J. 2009, 15, 13059−13068. (18) Zhang, L. F.; Fu, X. L.; Gao, G. H. Anion-Cation Cooperative Catalysis by Ionic Liquids. ChemCatChem 2011, 3, 1359−1364. (19) Fumino, K.; Wulf, A.; Ludwig, R. The Cation−Anion Interaction in Ionic Liquids Probed by Far-Infrared Spectroscopy. Angew. Chem., Int. Ed. 2008, 47, 3830−3834. (20) Zahn, S.; Uhlig, F.; Thar, J.; Spickermann, C.; Kirchner, B. Intermolecular Forces in an Ionic Liquid (Mmim Cl) versus Those in a Typical Salt (NaCl). Angew. Chem., Int. Ed. 2008, 47, 3639−3641. (21) Singh, T.; Rao, K. S.; Kumar, A. Effect of Ethylene Glycol and Its Derivatives on the Aggregation Behavior of an Ionic Liquid 1-Butyl3-methyl Imidazolium Octylsulfate in Aqueous Medium. J. Phys. Chem. B 2012, 116, 1612−1622. (22) Kossmann, S.; Thar, J.; Kirchner, B.; Hunt, P. A.; Welton, T. Cooperativity in Ionic Liquids. J. Chem. Phys. 2006, 124, 174506. (23) Blesic, M.; Lopes, A.; Melo, E.; Petrovski, Z.; Plechkova, N. V.; Lopes, J. N. C.; Seddon, K. R.; Rebelo, L. P. N. On the SelfAggregation and Fluorescence Quenching Aptitude of Surfactant Ionic Liquids. J. Phys. Chem. B 2008, 112, 8645−8650. (24) Wang, X. Q.; Yu, L.; Jiao, J. J.; Zhang, H. N.; Wang, R.; Chen, H. Aggregation Behavior of COOH-Functionalized Imidazolium-Based Surface Active Ionic Liquids in Aqueous Solution. J. Mol. Liquid. 2012, 173, 103−107. (25) Schrekker, H. S.; Silva, D. O.; Gelesky, M. A.; Stracke, M. P.; Schrekker, C. M. L.; Goncalves, R. S.; Dupont, J. Preparation, Cation− Anion Interactions and Physicochemical Properties of Ether-Function17887



Article

with Functionalized Ionic Liquids, Supported-Ionic Liquid Phase, or Ionic Liquid Media. Curr. Org. Chem. 2009, 13, 1322−1346. (44) Luo, S. Z.; Mi, X. L.; Zhang, L.; Liu, S.; Xu, H.; Cheng, J. P. Functionalized Ionic Liquids Catalyzed Direct Aldol Reactions. Tetrahedron 2007, 63, 1923−1930. (45) Hernandez, J. G.; Juaristi, E. Recent Efforts Directed to the Development of More Sustainable Asymmetric Organocatalysis. Chem. Commun. 2012, 48, 5396−5409. (46) Luo, S. Z.; Zhang, L.; Cheng, J. P. Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands. Chem.−Asian J. 2009, 4, 1184−1195. (47) Budagumpi, S.; Haque, R. A.; Salman, A. W. Stereochemical and Structural Characteristics of Single- And Double-Site Pd(II)-NHeterocyclic Carbene Complexes: Promising Catalysts in Organic Syntheses Ranging from C−C Coupling to Olefin Polymerizations. Coord. Chem. Rev. 2012, 256, 1787−1830. (48) Gu, Y. L.; Li, G. X. Ionic Liquids-Based Catalysis with Solids: State of the Art. Adv. Synth. Catal. 2009, 351, 817−847. (49) Bugaut, X.; Glorius, F. Organocatalytic Umpolung: NHeterocyclic Carbenes and Beyond. Chem. Soc. Rev. 2012, 41, 3511−3522. (50) Lee, J. W.; Shin, J. Y.; Chun, Y. S.; Bin Jang, H.; Song, C. E.; Lee, S. G. Toward Understanding the Origin of Positive Effects of Ionic Liquids on Catalysis: Formation of More Reactive Catalysts and Stabilization of Reactive Intermediates and Transition States in Ionic Liquids. Acc. Chem. Res. 2010, 43, 985−994. (51) Yang, Z. Hofmeister Effects: An Explanation for the Impact of Ionic Liquids on Biocatalysis. J. Biotechnol. 2009, 144, 12−22. (52) dos Santos, M. R.; Diniz, J. R.; Arouca, A. M.; Gomes, A. F.; Gozzo, F. C.; Tamborim, S. M.; Parize, A. L.; Suarez, P. A. Z.; Neto, B. A. D. Ionically Tagged Iron Complex-Catalyzed Epoxidation of Olefins in Imidazolium-Based Ionic Liquids. ChemSusChem 2012, 5, 716−726. (53) Peppel, T.; Roth, C.; Fumino, K.; Paschek, D.; Kockerling, M.; Ludwig, R. The Influence of Hydrogen-Bond Defects on the Properties of Ionic Liquids. Angew. Chem., Int. Ed. 2011, 50, 6661− 6665. (54) Fumino, K.; Reichert, E.; Wittler, K.; Hempelmann, R.; Ludwig, R. Low-Frequency Vibrational Modes of Protic Molten Salts and Ionic Liquids: Detecting and Quantifying Hydrogen Bonds. Angew. Chem., Int. Ed. 2012, 51, 6236−6240. (55) Dong, K.; Zhang, S. J. Hydrogen Bonds: A Structural Insight into Ionic Liquids. Chem.Eur. J. 2012, 18, 2748−2761. (56) Tsuzuki, S.; Tokuda, H.; Mikami, M. Theoretical analysis of the hydrogen bond of imidazolium C-2-H with anions. Phys. Chem. Chem. Phys. 2007, 9, 4780−4784. (57) Lassegues, J. C.; Grondin, J.; Cavagnat, D.; Johansson, P. New Interpretation of the CH Stretching Vibrations in Imidazolium-Based Ionic Liquids. J. Phys. Chem. A 2009, 113, 6419−6421. (58) Danten, Y.; Cabaco, M. I.; Besnard, M. Interaction of Water Highly Diluted in 1-Alkyl-3-methyl Imidazolium Ionic Liquids with the PF6− and BF4− Anions. J. Phys. Chem. A 2009, 113, 2873−2889. (59) Fei, Z. F.; Zhao, D. B.; Geldbach, T. J.; Scopelliti, R.; Dyson, P. J. Bronsted Acidic Ionic Liquids and Their Zwitterions: Synthesis, Characterization and pK(a) Determination. Chem.Eur. J. 2004, 10, 4886−4893. (60) Lissner, E.; de Souza, W. F.; Ferrera, B.; Dupont, J. Oxidative Desulfurization of Fuels with Task-Specific Ionic Liquids. ChemSusChem 2009, 2, 962−964. (61) Zhang, H.; Cui, H. Synthesis and Characterization of Functionalized Ionic Liquid-Stabilized Metal (Gold and Platinum) Nanoparticles and Metal Nanoparticle/Carbon Nanotube Hybrids. Langmuir 2009, 25, 2604−2612. (62) Li, J. Z.; Peng, Y. Q.; Song, G. H. Mannich Reaction Catalyzed by Carboxyl-Functionalized Ionic Liquid in Aqueous Media. Catal. Lett. 2005, 102, 159−162. (63) Oliveira, F. F. D.; dos Santos, M. R.; Lalli, P. M.; Schmidt, E. M.; Bakuzis, P.; Lapis, A. A. M.; Monteiro, A. L.; Eberlin, M. N.; Neto, B. A. D. Charge-Tagged Acetate Ligands As Mass Spectrometry Probes

for Metal Complexes Investigations: Applications in Suzuki and Heck Phosphine-Free Reactions. J. Org. Chem. 2011, 76, 10140−10147. (64) Lalli, P. M.; Rodrigues, T. S.; Arouca, A. M.; Eberlin, M. N.; Neto, B. A. D. N-heterocyclic carbenes with negative-charge tags: direct sampling from ionic liquid solutions. RSC Adv. 2012, 2, 3201− 3203. (65) Ramos, L. M.; Guido, B. C.; Nobrega, C. C.; Corrêa, J. R.; Silva, R. G.; de Oliveira, H. C. B.; Gomes, A. F.; Gozzo, F. C.; Neto, B. A. D. The Biginelli Reaction with an Imidazolium-Tagged Recyclable Iron Catalyst: Kinetics, Mechanism, and Antitumoral Activity. Chem.Eur. J. 2013, 19, 4156−4168. (66) Diniz, J. R.; Correa, J. R.; Moreira, D. d. A.; Fontenele, R. S.; de Oliveira, A. L.; Abdelnur, P. V.; Dutra, J. D. L.; Freire, R. O.; Rodrigues, M. O.; Neto, B. A. D. Water-Soluble Tb3+ and Eu3+ Complexes with Ionophilic (Ionically Tagged) Ligands as Fluorescence Imaging Probes. Inorg. Chem. 2013, 52, 10199−10205. (67) Medeiros, G. A.; da Silva, W. A.; Bataglion, G. A.; Ferreira, D. A. C.; de Oliveira, H. C. B.; Eberlin, M. N.; Neto, B. A. D. Probing the Mechanism of the Ugi Four-Component Reaction with ChargeTagged Reagents by ESI-MS(/MS). Chem. Commun. 2014, 50, 338− 340. (68) Ramos, L. M.; Tobio, A.; dos Santos, M. R.; de Oliveira, H. C. B.; Gomes, A. F.; Gozzo, F. C.; de Oliveira, A. L.; Neto, B. A. D. Mechanistic Studies on Lewis Acid Catalyzed Biginelli Reactions in Ionic Liquids: Evidence for the Reactive Intermediates and the Role of the Reagents. J. Org. Chem. 2012, 77, 10184−10193. (69) Medeiros, A.; Parize, A. L.; Oliveira, V. M.; Neto, B. A. D.; Bakuzis, A. F.; Sousa, M. H.; Rossi, L. M.; Rubim, J. C. Magnetic Ionic Liquids Produced by the Dispersion of Magnetic Nanoparticles in 1-nButyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide (BMI.NTf2). ACS Appl. Mater. Interfaces 2012, 4, 5458−5465. (70) Neto, B. A. D.; Meurer, E. C.; Galaverna, R.; Bythell, B. J.; Dupont, J.; Cooks, R. G.; Eberlin, M. N. Vapors from Ionic Liquids: Reconciling Simulations with Mass Spectrometric Data. J. Phys. Chem. Lett. 2012, 3, 3435−3441. (71) dos Santos, M. R.; Gomes, A. F.; Gozzo, F. C.; Suarez, P. A. Z.; Neto, B. A. D. Iron Complex with Ionic Tag-Catalyzed Olefin Reduction under Oxidative ConditionsA Different Reaction for Iron. ChemSusChem 2012, 5, 2383−2389. (72) Dubey, R.; Lim, D. Weak Interactions: A Versatile Role in Aromatic Compounds. Curr. Org. Chem. 2011, 15, 2072−2081. (73) Dupont, J.; Suarez, P. A. Z.; De Souza, R. F.; Burrow, R. A.; Kintzinger, J. P. C-H-π Interactions in 1-n-Butyl-3-methylimidazolium Tetraphenylborate Molten Salt: Solid and Solution Structures. Chem.Eur. J. 2000, 6, 2377−2381. (74) Consorti, C. S.; Suarez, P. A. Z.; de Souza, R. F.; Burrow, R. A.; Farrar, D. H.; Lough, A. J.; Loh, W.; da Silva, L. H. M.; Dupont, J. Identification of 1,3-Dialkylimidazolium Salt Supramolecular Aggregates in Solution. J. Phys. Chem. B 2005, 109, 4341−4349. (75) Dong, K.; Zhang, S. J.; Wang, D. X.; Yao, X. Q. Hydrogen Bonds in Imidazolium Ionic Liquids. J. Phys. Chem. A 2006, 110, 9775−9782. (76) Steiner, T. The Hydrogen Bond in the Solid State. Angew. Chem., Int. Ed. 2002, 41, 48−76. (77) Vold, R. L.; Waugh, J. S.; Klein, M. P.; Phelps, D. E. Measurement of Spin Relaxation in Complex Systems. J. Chem. Phys. 1968, 48, 3831−3832. (78) Desando, M. A.; Lahajnar, G.; Sepe, A. Proton Magnetic Relaxation and the Aggregation of n-Octylammonium n-Octadecanoate Surfactant in Deuterochloroform Solution. J. Colloid Interface Sci. 2010, 345, 338−345. (79) Zhao, Y.; Gao, S. J.; Wang, J. J.; Tang, J. M. Aggregation of Ionic Liquids C(n)mim Br (n = 4, 6, 8, 10, 12) in D2O: A NMR Study. J. Phys. Chem. B 2008, 112, 2031−2039. (80) Remsing, R. C.; Liu, Z. W.; Sergeyev, I.; Moyna, G. Solvation and Aggregation of N,N ′-Dialkylimidazolium Ionic Liquids: A Multinuclear NMR Spectroscopy and Molecular Dynamics Simulation Study. J. Phys. Chem. B 2008, 112, 7363−7369. 17888



Article

(81) Martins, C. T.; Sato, B. M.; El Seoud, O. A. First Study on the Thermo-Solvatochromism in Aqueous 1-(1-Butyl)-3-methylimidazolium Tetrafluoroborate: A Comparison between the Solvation by an Ionic Liquid and by Aqueous Alcohols. J. Phys. Chem. B 2008, 112, 8330−8339. (82) Ananikov, V. P. Characterization of Molecular Systems and Monitoring of Chemical Reactions in Ionic Liquids by Nuclear Magnetic Resonance Spectroscopy. Chem. Rev. 2011, 111, 418−454. (83) Spickermann, C.; Thar, J.; Lehmann, S. B. C.; Zahn, S.; Hunger, J.; Buchner, R.; Hunt, P. A.; Welton, T.; Kirchner, B. Why Are Ionic Liquid Ions Mainly Associated in Water? A Car-Parrinello Study of 1Ethyl-3-methyl-imidazolium Chloride Water Mixture. J. Chem. Phys. 2008, 129, 104505. (84) Singh, T.; Kumar, A. Cation-anion-water interactions in aqueous mixtures of imidazolium based ionic liquids. Vib. Spectrosc. 2011, 55, 119−125. (85) Bowers, J.; Butts, C. P.; Martin, P. J.; Vergara-Gutierrez, M. C.; Heenan, R. K. Aggregation Behavior of Aqueous Solutions of Ionic Liquids. Langmuir 2004, 20, 2191−2198. (86) Singh, T.; Kumar, A. Aggregation Behavior of Ionic Liquids in Aqueous Solutions: Effect of Alkyl Chain Length, Cations, And Anions. J. Phys. Chem. B 2007, 111, 7843−7851. (87) Zhang, H. C.; Liang, H. J.; Wang, J. J.; Li, K. Aggregation Behavior of Imidazolium-Based Ionic Liquids in Water. Z. Phys. Chem. 2007, 221, 1061−1074. (88) Neumann, B. On the Aggregation Behavior of Pseudoisocyanine Chloride in Aqueous Solution As Probed by UV/vis Spectroscopy and Static Light Scattering. J. Phys. Chem. B 2001, 105, 8268−8274. (89) Vila, J.; Gines, P.; Rilo, E.; Cabeza, O.; Varela, L. M. Great Increase of the Electrical Conductivity of Ionic Liquids in Aqueous Solutions. Fluid Phase Equilib. 2006, 247, 32−39. (90) Wang, Y. D.; Cakmak, M. Spatial Variation of Structural Hierarchy in Injection Molded PVDF and Blends of PVDF with PMMA. Part II. Application of Microbeam WAXS Pole Figure and SAXS Techniques. Polymer 2001, 42, 4233−4251. (91) Korgel, B. A.; Fitzmaurice, D. Small-Angle X-Ray-Scattering Study of Silver-Nanocrystal Disorder-Order Phase Transitions. Phys. Rev. B 1999, 59, 14191−14201. (92) Verma, R.; Marand, H.; Hsiao, B. Morphological Changes During Secondary Crystallization and Subsequent Melting in Poly(Ether Ether Ketone) as Studied by Real Time Small Angle X-Ray Scattering. Macromolecules 1996, 29, 7767−7775. (93) Ficke, L. E.; Brennecke, J. F. Interactions of Ionic Liquids and Water. J. Phys. Chem. B 2010, 114, 10496−10501. (94) Lopes, J. N. C.; Gomes, M. F. C.; Padua, A. A. H. Nonpolar, Polar, and Associating Solutes in Ionic Liquids. J. Phys. Chem. B 2006, 110, 16816−16818. (95) Schatzbe., P. On Molecular Diameter of Water from Solubility and Diffusion Measurements. J. Phys. Chem. 1967, 71, 4569−4570. (96) Perera, A.; Sokolic, F.; Zoranic, L. Microstructure of Neat Alcohols. Phys. Rev. E 2007, 75, 060502. (97) Kemp, D. D.; Gordon, M. S. Theoretical Study of the Solvation of Fluorine and Chlorine Anions by Water. J. Phys. Chem. A 2005, 109, 7688−7699. (98) Dupont, J.; Eberlin, M. N. Structure and Physico-Chemical Properties of Ionic Liquids: What Mass Spectrometry is Telling Us. Curr. Org. Chem. 2013, 17, 257−272. (99) Alvim, H. G. O.; de Lima, T. B.; de Oliveira, H. C. B.; Gozzo, F. C.; de Macedo, J. L.; Abdelnur, P. V.; Silva, W. A.; Neto, B. A. D. Ionic Liquid Effect over the Biginelli Reaction under Homogeneous and Heterogeneous Catalysis. ACS Catal. 2013, 3, 1420−1430. (100) Alvim, H. G. O.; Lima, T. B.; de Oliveira, A. L.; de Oliveira, H. C. B.; Silva, F. M.; Gozzo, F. C.; Souza, R. Y.; da Silva, W. A.; Neto, B. A. D. Facts, Presumptions, and Myths on the Solvent-Free and Catalyst-Free Biginelli Reaction. What is Catalysis for? J. Org. Chem. 2014, 79, 3383−3397. (101) Alvim, H. G. O.; Bataglion, G. A.; Ramos, L. M.; de Oliveira, A. L.; de Oliveira, H. C. B.; Eberlin, M. N.; de Macedo, J. L.; da Silva, W. A.; Neto, B. A. D. Task-Specific Ionic Liquid Incorporating Anionic

Heteropolyacid-Catalyzed Hantzsch and Mannich Multicomponent Reactions. Ionic Liquid Effect Probed by ESI-MS(/MS). Tetrahedron 2014, 70, 3306−3313. (102) Kitaura, K.; Sakaki, S.; Morokuma, K. Bonding in Ni(PH3)2(C2H4) and Ni(PH3)2(C2H2). Ab Initio SCF-MO Study. Inorg. Chem. 1981, 20, 2292−2297. (103) Bader, R. F. W.; Popelier, P. L. A.; Keith, T. A. Theoretical Definition of a Functional-Group and the Molecular-Orbital Paradigm. Angew. Chem., Int. Ed. 1994, 33, 620−631. (104) Bone, R. G. A.; Bader, R. F. W. Identifying and Analyzing Intermolecular Bonding Interactions in Van der Waals Molecules. J. Phys. Chem. 1996, 100, 10892−10911. (105) Hernandez-Trujillo, J.; Bader, R. F. W. Properties of Atoms in Molecules: Atoms Forming Molecules. J. Phys. Chem. A 2000, 104, 1779−1794. (106) Bader, R. F. W. A Bond Path: A Universal Indicator of Bonded Interactions. J. Phys. Chem. A 1998, 102, 7314−7323. (107) Koch, U.; Popelier, P. L. A. Characterization of C-H-O Hydrogen Bonds on the Basis of the Charge Density. J. Phys. Chem. 1995, 99, 9747−9754. (108) Shishkin, O. V.; Palamarchuk, G. V.; Gorb, L.; Leszczynski, J. Intramolecular Hydrogen Bonds in Canonical 2′-Deoxyribonucleotides: An Atoms in Molecules Study. J. Phys. Chem. B 2006, 110, 4413−4422.

17889


Structural Organization and Supramolecular Interactions of the Task

Recommend Documents