1H NMR Relaxometry and Diffusometry Study of Magnetic and

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H NMR Relaxometry and Diffusometry Study of Magnetic and NonMagnetic Ionic Liquid-Based Solutions: Co-Solvent and Temperature Effects Maria Jardim Beira, Carla I. Daniel, Pedro L. Almeida, Marta C. Corvo, Andreia A. Rosatella, Carlos A. M. Afonso, and Pedro J. Sebastiao J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b07929 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 30, 2017

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The Journal of Physical Chemistry

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H NMR Relaxometry and Diffusometry Study of

Magnetic and Non-Magnetic Ionic Liquid-Based Solutions: Co-Solvent and Temperature Effects Maria Beira,† Carla I. Daniel,‡ Pedro L. Almeida,¶ Marta C. Corvo,¶ Andreia A. Rosatella,§ Carlos A. M. Afonso,§ and Pedro J. Sebastião∗,† †Center of Physics and Engineering of Advanced Materials, Departamento de F´ısica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal ‡REQUIMTE/LAQV, Departamento de Qu´ımica, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal ¶CENIMAT- Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal §Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003, Lisboa, Portugal E-mail: [email protected]

Abstract In this work, 1 H NMR relaxometry and diffusometry as well as viscometry experiments were carried out as a means to study the molecular dynamics of magnetic and non-magnetic ionic liquid-based systems. In order to evaluate the effect of a co-solvent on the super-paramagnetic properties observed for Aliquat-iron-based magnetic ionic liquids, mixtures comprising different concentrations, 1% and 10% (v/v), of DMSO-d6

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were prepared and studied. The results for both magnetic and non-magnetic systems were consistently analyzed an suggest that, when at low concentrations, DMSO-d6 promotes more structured ionic arrangements, thus enhancing these super-paramagnetic properties. Furthermore, the analysis of temperature and water concentration effects allowed to conclude that neither one of these variables significantly affected the superparamagnetic properties of the studied magnetic ionic liquids.

Introduction Understanding the molecular interactions has been one of the main targets of different scientific studies regarding pure liquids and mixtures. It is fundamental to know the characteristics and structure of the compounds involved in a liquid matrix in order to understand ion-ion and ion-solvent interactions. 1 The versatility and unique physico-chemical properties of ionic liquids, ILs, make them one of the most studied systems, having distinct applicability in fields such as electrochemistry, novel chemical synthesis, biocatalysis, and biology. 2–4 ILs are a special class of chemical compounds which combine the organic nature of organic solvents and the ionic nature of inorganic salts. They are characterized by an extremely low volatility, good solvation ability, high thermal and chemical stability and high conductivity. In addition, their properties can be widely tuned by properly choosing the cation-anion combination. 5–7 Although the organic and ionic nature of these compounds have been deeply explored, their microscopic physical behavior due to the interactions between the ions is not clearly understood. 5 Experimental approaches based on spectroscopy techniques, namely IR and NMR, and distinct molecular dynamics simulation tools have been used to study different physical and chemical properties of pure liquids and binary or ternary systems. 5–12 For a variety of ILs, whose cations are characterized by different alkyl chain lengths, it is known that the chains tend to segregate from the polar parts, creating non-polar domains, and that the charged species constitute an ionic network. 5 2


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Regarding IL/co-solvent systems, which have been attracting substantially larger interest when compared with pure ILs, the balance formation of the ion pairs (ion-solvent and cationanion interactions in solution) is one of the features that most influences their physicochemical properties - viscosity, density, polarity, solvation ability, self-diffusion and response to external stimuli (e.g. magnetic, electric, pH). Furthermore, ionic-dipole and hydrogenbonding can also play a fundamental role in the molecular interactions and local molecular organization, as shown in recent studies of ILS/DMSO mixtures. 6,13–16 A study by Tokuda et al. 17 on mixtures comprising ammonium cation-based ILs and either propylenecarbonate or 1,2 dichloroethane shows that the addition of these organic solvents promoted the ionic association and contributed to an increase of the ionic diffusion. Li et al. 6 also concluded that organic solvents (namely acetone, chloroform and pyridine) enhance the ionic association when added to ILs, while water produces the opposite effect because of its high dielectric constant and ability to form strong bonds with the anions. In this work it was also shown that the solvents significantly affected the density, viscosity and conductivity of the studied imidazolium-based ionic liquids. In addition, a more recent comparative study regarding solutions of ionic liquids based on different cations and anions - IL/H2 O and IL/DMSO- shows that the water molecules seem to have the ability to break cation-anion bonds and that DMSO has a weaker solvation ability, giving rise to ion pairs or clusters and only to a small amount of free ions in these mixtures. 14 A particular subgroup of ILs, magnetic ionic liquids (MILs), has gained relevance over the last few years, since their physico-chemical properties can be changed when the system is subjected to an external magnetic field. The dependence between the local molecular organization and the external stimuli, potentially enables the latter to affect the charge distribution in MILs and, thus, their viscosity, solubility and/or ability to solvate other chemical compounds. 18–22 In recent works, Daniel et al. 21 ,22 studied the molecular dynamics of IL/MIL and MIL/DMSO systems using 1 H-NMR relaxometry. The results have shown that mixtures containing mag-

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netic and non-magnetic ionic liquids, exhibit super-paramagnetic properties 21,22 as the ones observed for systems comprising iron oxide nanoparticles. This relaxation behavior was related to a possible coupling of the magnetic moments of the anions in the system. Moreover, the pronounced super-paramagnetic effect observed for the phosphonium salt-based IL/MIL mixture was not detected when the non-magnetic ionic liquid was replaced by DMSO. These results suggest a different local molecular interaction in IL/MIL and DMSO/MIL systems due to their obviously different structure and nature. 22 The distinct physical behaviors of MIL/solvent mixtures motivated the present work, performed as a way to better understand the influence of ion-ion and ion-solvent interactions in their physico-chemical properties, namely, viscosity, self-diffusion and in the superparamagnetic behavior. 1 H-NMR (relaxometry and diffusometry) and viscometry measurements (under different magnetic field conditions) were conducted on Aliquat based magnetic and non-magnetic ionic liquids comprising different concentrations, 1% and 10% (v/v), of DMSO-d6. The use of fully deuterated dimethylsulfoxide made it possible to study the proton spin relaxation of the protonated molecular species in the mixtures, namely the [Aliquat]+ ions. The effect of water, as a co-solvent, in the properties and magnetic behavior of the Aliquat-based systems was analyzed and relaxometry studies at different temperatures were also performed.

Experimental Materials Several ionic liquid samples were studied in this work: [Aliquat][Cl], mixtures of [Aliquat][Cl] and [Aliquat][FeCl4 ], and mixtures of these ionic liquids with deuterated dimethylsulfoxide. [Aliquat][Cl] and [Aliquat][FeCl4 ] were synthesized according to the procedure reported in the literature. 23,24 In Table 1 are presented the water content, average molar mass, and density of the stud4


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Table 1: Water content, average molar mass, and density of the studied samples. (*) Values reported by Daniel et al. 21 . “aged” refers to new values obtained for aged samples. Water Content (% wt)

Average Molar Mass (g.mol−1 )

(g.cm−3 )

5.8*

404.2 –

0.88* –

(aged: 7.9)

405.8 –

1.03* –

[Aliquat][Cl] / (1% v/v) DMSO-d6

3.0

401.0

0.884

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ] / (1% v/v) DMSO-d6

2.3

402.6

0.893


2.8

372.2

0.912

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ] / (10% v/v) DMSO-d6

2.1

373.8

0.915

IL

[Aliquat][Cl]

(aged: 7.9)

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ]

5.5*

Density

ied mixtures. The water content was estimated using the values obtained by Karl Fisher titration for the separate components in the mixtures and taking the respective volume percentage into account; the average molar mass of the mixtures was also determined taking into consideration the individual components ratio; and the density was measured gravimetrically at 25o C, using a picnometer. The concentration of magnetic particles was determined through Flame Atomic Absorption Spectroscopy, leading to the values of 0.0144 and 0.0147 mol L−1 for the magnetic ionic liquids mixed with 1 and 10% DMSO-d6, respectively. Regarding the samples studied by Daniel et al. 21 , which were not mixed with DMSO, a value

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of 0.012 mol L−1 was reported.

Methods Viscosity Measurements The viscosity of the analyzed systems was measured through capillary viscometry, according to the procedure described in reference 25 and considering an uncertainty of 0.003 Pa · s. The dependence of the viscosity on the applied magnetic field was determined using a home-built system composed of a glass capillary Ubbelohde viscometer – 3C, manufactured and calibrated by the Cannon Instrument company, placed between a GMW dipole electromagnet 3473-70 with a 75 mm pole gap (by GMW Associates, USA) at controlled temperature. The details of the setup are presented in the supporting information, SI (Figure S1). All viscosity measurements were made at 25 ± 1 o C.

Nuclear Magnetic Resonance The spin-lattice relaxation time, T1 =R1−1 , was measured with a 10% uncertainty, using two complementary experimental techniques and three different spectrometers, in order to cover a broad frequency range. From 10kHz to 9MHz the T1 was measured with a homedeveloped fast field-cycling (FFC) relaxometer, operating with a polarisation and detection fields of ≈ 0.215T and a switching time less than 3 ms. 26 A variable field (0.2 - 2T) iron-core electromagnet and a Bruker 7T superconductor magnet, both paired with a Bruker Avance II spectrometer, were used to measure the spin-lattice relaxation time across the 10-100MHz frequency range and at 300MHz, respectively. The measurements above 10MHz were all performed from the lowest to the highest magnetic field, using the conventional inversion recovery pulse sequence with phase cycling, to remove the DC bias components from the signal.

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1

H NMR spectra were obtained at 25o C, using the Bruker Avance II spectrometer op-

erating at 300MHz, for the [Aliquat][Cl]-based samples, studied by Daniel et al. 21 , for the aged [Aliquat][Cl]-based samples and the new samples mixed with DMSO-d6. The self diffusion coefficient, D, was measured using a pulsed gradient stimulated echo sequence, 27 a Bruker Diff 30 probe (or a micro-imaging probe), a magnetic field gradient unit and a Bruker7 T superconductor connected to a Bruker Avance III NMR console. In this case, the increase of the magnetic field gradient leads to an attenuation of the free induction decay signal, expressed by the following equation: ∆ 1 2 2 3 − , I = I0 exp −γ1 H G Dδ δ 3

(1)

where γ1 H is the proton gyromagnetic ratio, G is the gradient strength, δ is the length of the gradient pulses and ∆ is the delay between pulsed gradients. In these NMR experiments, the temperature was controlled by the heating or cooling of a continuous compressed air flux and was measured with a 0.5 o C uncertainty.

Results The viscosity is one of the properties of magnetic ionic liquids that can be affected by the applied external magnetic field. In order to evaluate this dependence, viscosity measurements at different magnetic field strengths were performed and the obtained results are summarized in Table 2. The translational self-diffusion constant was obtained fitting equation 1 to the experimental echo intensity decay signal obtained for different values of ∆ and δ. Some results dispersion was observed depending on the specific NMR probe used (Bruker Diff 30 or a micro-imaging probe) and on the measurement parameters settings (∆ and δ). In Table 2 is presented an average of all the measured values with different experimental conditions. For the samples composed of metal ions, a small viscosity decrease was detected between the

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values measures at 0 and 2 Tesla. A more accurate variation profile could not be obtained because the setup represented in Figure S1 does not allow for a good temperature control. In fact, during the measurements the temperature could vary up to 2o C and this can mask and affect the small magnetic field dependence observed for these magnetic ionic liquids mixed with DMSO-d6. The experimental NMR relaxometry results obtained for the samples comprising DMSOd6 in their composition are presented in Figure 1 along with the results obtained by Daniel et al. 21 , in the absence of this co-solvent. For all the studied samples it was observed a biexponential behavior of the longitudinal relaxation time, as also reported in. 21 This biexponential behavior was assigned to the existence of two different spin populations within the cation chemical structure: the more rigid (CH2) and more mobile (CH3) parts of the aliphatic chains. In fact, the [Aliquat]+ cation is composed of four aliphatic chains, three of which are quite long (see Figure 2) and its charge is located at the central nitrogen atom. R1,CH2 and R1,CH3 are the relaxation rates of the two spin populations, but the indexes CH2 and CH3 are merely a way of simplifying the notation. The ratio between spin populations was kept constant and fixed to the same value used by Daniel et al. 21 , considering the terminal methylene and methyl groups as the more mobile section and the remaining methylene groups as the more rigid part. In Figure 1, a) - c), and Figure 1, b) - d), are presented the obtained relaxation rate results for both spin population of the [Aliquat][Cl] / [Aliquat][FeCl4 ] mixtures and for the non-magnetic [Aliquat][Cl] solutions, respectively. By closely observing the high frequency range in Figure 1, a) - c), it can be seen that R1,CH2 and R1,CH3 increase with the addition of 1% (v/v) of DMSO-d6, but adding 10% (v/v) of DMSO-d6 does not produce a further increase. In fact, the relaxation rate for the two spin populations decreases with respect to the ones obtained for the samples mixed with 1% (v/v) of DMSO-d6. In Figure 1, b) - d), across the low frequency range, R1,CH2 and R1,CH3 increase when

8


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adding 1% (v/v) of DMSO-d6 and this effect is reversed when adding 10% (v/v) of the same co-solvent. Although the increase observed for the [Aliquat][Cl] + 1% (v/v) DMSOd6 mixture could also be associated with water content differences, this reversed effect is in agreement with the 1 H NMR spectra obtained for the non-magnetic samples, which are presented in Figure 3. The addition of 1% (v/v) DMSO-d6 seems to cause a broadening of the NMR lines, comparing with the neat [Aliquat][Cl] while a 10% concentration of the DMSO-d6 leads to a spectral line narrowing. These results suggest that, for larger concentrations of DMSO, there is a micro-segregation effect, leading to the appearance of micro-domains with different concentrations of DMSO. There is also the possibility for these microdomains to disperse away from the polar regions. This micro-segregation/aggregation effect depennding on the concentration of the doping particles which has been observed for systems containing nanoparticles dispersed in polymers. In fact, for some of these systems, aggregation of nanoparticles above a critical concentration has been reported. 28 Spin lattice relaxation profiles were obtained for old samples of [Aliquat][Cl] and [Aliquat][Cl] + 1% (v/v) [Aliquat][FeCl4 ] (originally studied in 21 ) at 5, 25 and 70 o C, and the results for the less mobile spin population are presented in Figure 4 a) and b), respectively. By comparing the raw relaxometry data presented in Figure 4 a) and b) it is clear that the temperature variation produces a much larger effect on the non-magnetic system, especially from 25 to 70 o C. However, it is interesting to note that the NMRD profiles obtained at 5 and 25 o C present very small differences both for the magnetic and non-magnetic studied systems.

Analysis and Discussion Theoretical Model In general, any process that induces fluctuations of the magnetic field in the vicinity of a nucleus is a possible relaxation mechanism and it is usually possible to write each relaxation 9



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mechanism as: T1−1 = R1 = Ec2 f (τi ),

(2)

where Ec is the associated strength and τi are correlation times (e.g. average time between molecular collisions, characteristic rotation times, etc). In a large number of cases, there is a coexistence of several of these relaxation mechanisms, but given the different time scales at which they occur and/or their statistical independence, the total relaxation rate is well approximated by the sum of the several relaxation rate contributions:

1 = T1

1 T1

"

+ Rot1

1 T1

#

Rot2 CH2

+

1 T1

CR

1 + T1 SD 1 + . T1 P M MIL

(3)

In equation 3 are included the relevant contributions to the longitudinal relaxation in the studied systems. The subscripts Rot, SD, CR and P M represent the contribution from rotational diffusion, translational self diffusion, 1 H -

35

Cl cross-relaxation and paramagnetic

relaxation, respectively. The paramagnetic relaxation contribution is required to analyze the systems composed of metal ions ([FeCl4 ]). Rotational diffusion, Rot1 /Rot2 To the authors knowledge there is no specific theoretical model to describe the rotational dynamics of molecules such as the [Aliquat]+ cations. In previous studies ( 21,22 ) it was shown that it is possible to describe the rotation and reorientations of such molecules using the sum of two Bloembergen, Purcell and Pound (BPP) contributions to account for the different mobility of the molecules/molecular sections. The frequency dependence of each

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BPP relaxation rate is given by:

1 T1

= ARoti

Roti

τRoti 4τRoti , + 2 2 4τ 2 1 + ω 2 τRot 1 + ω Rot i i

(4)

with ARoti = 9µ20 γ14H h ¯ 2 /(128π 2 ri6ef f ), where rief f is the effective distance between intramolecular spins. 29

Translational diffusion, SD This relaxation mechanism is better described by the Torrey model for translational diffusion. 30 The model was derived from the aforementioned BPP model in order to improve the diffusion treatment, which was admittedly crude. Torrey assumes a random jump like solution where the molecules have equal probabilities of jumping in any direction from an initial state into another. The longitudinal relaxation time contribution is the following:

1 T1

= Cd SD

nτD [T (ωτD ) + 4T (2ωτD )] , d3

(5)

where, 1 Cd = 2

¯ 3µ0 γ12H h 8π

2 .

(6)

T (ωτD ) is an analytical and dimensionless function which depends on the average time between jumps, the mean square jump distance and on the lateral distance between neighboring molecules, d. In practice, the [Aliquat]+ cations can present a global cylindrical shape, when the three long chains are stretched and packed parallel to each other. The mean square jump distance is related to the diffusion constant through:

2 r = 6τD D.

(7)

For magnetic ionic liquids, it has been observed that the viscosity and diffusion constant can be magnetic field dependent. In previous studies ( 21,22 ) the diffusion constant dependence 11



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on the external magnetic field was well explained by the following empirical model:

D = D0 [1 + (γ1 H Bτv2 )p2 ],

(8)

where τv2 and p2 are parameters which explain the diffusion constant increase for increasing magnetic field strengths. Furthermore, for these systems, it was observed that the self diffusion coefficient can be related to the viscosity through the equation: √ T α , D=C η

(9)

1/2

with C = 7.48 × 10−8 Mw /(V 0.6 ), Mw being the molecular weight and V the molar volume. Basically, for liquids with polar molecules, such as ionic liquids, the Stokes-Einstein equation has to take into account the strong electrostatic forces between the ions and, therefore, an association degree, α, is used.

Cross-relaxation, CR When different nuclear species exist, it is possible to observe cross relaxation, as a consequence of the establishment of an equilibrium temperature between the nuclear spins. If the spin systems are mainly described by the dipolar interaction, this type of relaxation would only be relevant if the gyromagnetic ratios of the different nuclei were similar to each other. However, the effects of cross relaxation can be observed if one of the spin systems is associated with a quadrupolar moment (only for spins larger than

1 2

) . 31

As it can be seen in Table 1, all the ILs are based on anions which contain chlorine. Its most abundant isotope is

35

Cl (∼ 76%), characterized by a nuclear spin of 3/2. In previous

studies ( 21,22 ) 35 Cl - 1 H cross-relaxation contributions to the longitudinal relaxation rate were

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observed for Aliquat-based systems. This contribution is given by:

1 T1

= ACRi CRi

τCRi , 2 1 + (ω − ωCRi )2 τCR i

(10)

where ACRi describes the strength of the interaction and τCRi its characteristic time for each of the ωCRi frequencies associated with the quadrupolar hamiltonean of the

35

Cl spin

system. 32 From equation 10 it is possible to observe that when ω = ωCRi the cross relaxation contribution reaches a maximum value.

Paramagnetic Relaxation, P M To describe the paramagnetic relaxation, the outer-sphere relaxation model was used. This approach applies to protons which move or diffuse close to magnetic ions or particles but do not bind with them. In references 21,22 this model successfully fits to the experimental results obtained for magnetic ionic liquids and explains the high frequency behavior of the used compounds, which are very similar to the ones that were studied in this work. The relaxation rate contribution from the outer-sphere model is given by: 33,34

1 T1

( = 6τd c Sc2 J1 (ω, τd , τs → ∞)

PM

) i x − Sc2 J1 (ω, τd , τs ) , −Sc cotan 2S

(11)

where x = S¯ hγe B0 /(kT ) and c can be written as:

c=

16π h ¯ 2 NA [M ]γe γ1 H . 135000 r3

(12)

NA is the Avogadro’s number, [M ] is the molar concentration of magnetic particles (in moles per liter), r is the distance of closest approach between ions, S is the electronic spin along

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the applied magnetic field, τd is the diffusion time constant and equal to hr2 i /D, τs is the longitudinal electronic relaxation time and Sc can be written as: ω 1 ω 2S + 1 −1 −1 tanh (2S + 1) − tanh , Sc = 2 ωr 2 ωr

(13)

with ωr = 2γ1 H kT /(¯hγe ). The spectral densities in equation 11 are given by: J1 (ω, τd , τs ) = Re

1 + ε1/2 /4 1 + ε1/2 + 4ε/9 + ε3/2 /9

,

(14)

where ε = (iω + 1)τd /τs .

Model Fitting The NMR dispersion results obtained for the studied samples, which are listed in Table 1, were fitted to the theoretical model described by equation 3, using a non-linear least squares method with a global minimum target. 35 In this equation, the index MIL marks the term that was used only for the samples comprising magnetic particles. The index CH2 associates with an additional term used to describe the more complex rotation/reorientation dynamics of the more rigid part of the long aliphatic chains. The complete set of fitting reports for all the samples, as well as a summary of the fitting parameters obtained for the best fits, are provided in the supporting information, in Table 3 and in Table 4. In Figure 5 are presented the best model fitting curves to the experimental results shown in Figure 1 regarding the samples which contain a 10% (v/v) concentration of DMSO-d6. The associated fitting parameters and respective uncertainties are listed in Table 3. For the majority of the parameters it was possible to estimate an uncertainty from the variation of the global fits χ2 associated to each fitting variable independently, within a confidence level of 68%. However, for some CR and Rot2 parameters it was only possible to estimate an approximate value. 14


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The fitting process was made simultaneously for the samples containing [Aliquat][FeCl4 ] and for the analogous non-magnetic samples, characterized by the same co-solvent concentration and lacking the metal ions. In addition, both R1,CH2 and R1,CH3 experimental NMRD results were fitted together (see Figure 5). In this way, it was possible to better decouple the paramagnetic relaxation contribution from the remaining mechanisms and, to some extent, use the results obtained for the non-magnetic ionic liquid as a starting point to establish the baseline for the NMRD data of the magnetic system. As the diffusion measurements were performed at 7 T, the self-diffusion relaxation model was expressed in terms of diffusion constant at 7 T, taking into account the magnetic field dependence described by the empirical model of equation 8. This allowed for a direct comparison between the values measured through NMR diffusometry and those obtained from the fit, presented in Table 2 and 3, respectively (see also SI). Furthermore, in order to avoid over-parameterization the same value of r was considered for the distance of closest approach between ions in the paramagnetic relaxation model and for the mean jump distance in the translational diffusion model. The spin density, estimated using the density and molecular weight of the samples, and the density of magnetic particles were fixed parameters (see Table 3). In the absence of magnetic particles, the sample mixed with 1% (v/v) of DMSO-d6 presented a decrease in the diffusion constant according to both the relaxometry and diffusometry results, which, in view of the classical Stokes-Einstein relation, is not expected, given the decrease in viscosity measured - comparing with the values reported by Daniel et al. 21 for the neat [Aliquat][Cl] (see Table 2). Clearly, taking equation 9 into account, this can be understood if the association factor, α, also decreases for a 1% DMSO concentration. Moreover, the determined average intermolecular distance, d, which is, in practice, the distance between the cations, is different for each spin population and smaller in the case of the methylene groups, closer to the nitrogen atom. This suggests that DMSO, at low concentrations, contributes to a more compact ionic aggregation and provides a more

15



structured environment. Since the cations are the same for the magnetic and non-magnetic systems, it is possible to conclude that the more compact structure created by the addition of low DMSO-d6 concentrations is one of the reasons for the enhanced superparamagnetic properties of the analogous magnetic systems. However, in the case of the samples containing the [FeCl4 ]− ions, a diffusion coefficient decrease with the addition of DMSO was not detected. This happens, possibly, due to a more pronounced affinity between DMSO and the iron anionic complex, which reduces the effect on the aliphatic chains and explains why a global fit could be obtained using only one value of d for R1,CH2 and R1,CH3 , as observed for the systems without DMSO. Since DMSO is a polar solvent, a preferred interaction with the polar regions of the ionic species could be expected, both for the magnetic and non-magnetic systems. However, it has been reported that, when at low concentrations, such as the ones used in this study, DMSO prefers to interact with the cations (for ionic liquids with similar cationic structures) 14,36 and, therefore, a change in the dynamics of the protonated aliphatic chains of the cation can occur, as the relaxometry results presented here also suggest. In view of the effect of DMSO in the local molecular organization, it is reasonable to assume that the cross-relaxation mechanism between the hydrogen protons and the chlorine nuclei might be different (comparing to the samples without DMSO studied by Daniel et al. 21 ) as a result of the change in the electric field gradient at the chlorines site. In the non-magnetic systems studied here, it was not possible to clearly identify the characteristic R1 cusps as observed by Daniel et al. 21 for the samples without DMSO. Nevertheless, the cross-relaxation contribution is definitely needed to fully describe the results and, therefore, a single contribution from this relaxation mechanism was used, either for R1,CH2 and R1,CH3 , for the sake of simplicity. Furthermore, the considered CR contribution was fixed in the model used to fit the data obtained for the analogous magnetic ionic liquid, since it is completely masked by that of the paramagnetic relaxation mechanism. The presence of increasing concentrations of DMSO-d6 in the samples leads to a de-

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crease of the correlation times associated with fast rotations/reorientation (Rot1), which is consistent with the faster molecular motions produced by the decrease in viscosity. On the other hand, with the exception of the electronic relaxation time, τs , the fitting parameters associated with the paramagnetic relaxation mechanism seem to be in agreement with the aforementioned reversed behavior observed in the raw relaxometry data and in the 1 H NMR spectra, presented in Figures 1 and 3, respectively. Clearly, adding 10% (v/v) DMSO-d6 does not accentuate the effect of the addition of 1% (v/v) of the same co-solvent (see Table 3). The slow rotations/reorientations relaxation contributions (Rot2), considered in the analysis of R1,CH2 , are clearly more effective across the low frequency range of the relaxation dispersion curve (see Figure 1, c) - d)), competing with the translational diffusion contribution. Therefore, aside from accounting for the cations anisometry, these slower rotation, can be partly seen as a correction to the self diffusion model used in the data analysis, in view of its oversimplified nature. The Torrey model does not take into account possible aliphatic chain interdigitations which can occur for complex systems such as the [Aliquat]+ cation. It is important to note that , despite the oversimplified translational diffusion model considered and the experimental difficulties encountered during the PFG NMR experiments (whose result depends on (δ, ∆ and the maximum magnetic field gradient applied)), the self diffusion results obtained by fitting the proton spin-lattice relaxation dispersion data and those obtained through 1 H NMR diffusometry are consistent and the fitted diffusion constants were set as close as possible to the values obtained by PFG NMR without changing the theoretical model used for each of the studied systems. New experiments at 25o C were performed in previously studied samples 21 in order to determine whether the longitudinal relaxation dispersion presented the same behavior as reported in this reference. In Figure 6 are presented the results obtained for the aged samples and those reported by Daniel et al. 21 for freshly prepared samples. In addition, the best model fitting curves for the aged samples are also presented.

17



From the analysis of Figure 6 it is clear that the relaxation rate dispersion results obtained for the fresh and aged samples are characterized by the same overall profile, but the latter present a slight decrease across the entire frequency range, consistent with an increase of the diffusion coefficient. This increase is supported by the obtained relaxometry and diffusometry results (see supporting information). In Figure S2 are presented the 1 H NMR spectra, normalized to the maximum peak intensity, obtained at 7 Tesla for both the aged and fresh samples. The line at around 4 ppm chemical shift, usually associated with the water signal, puts in evidence a larger water content in the aged sample, possibly, as a result of absorption within the storage time. The relative intensity of the water peaks in the spectra is consistent with a 1 to 2% water absorption by these aged samples, confirmed by Karl Fisher titration (see Table 1). As previously observed for the samples mixed with DMSO, the presence of water as a co-solvent in a larger concentration seems to affect the molecular organization of the ion pairs and, thus, the diffusion constant. From the relaxometry results, it is clear that the super-paramagnetic relaxation effect is still present in the aged system. The results show, however, a slight reduction of the super-paramagnetic properties, which is consistent with water having the ability to break the ionic bonds, even when at low concentrations, as reported in the works of Zhao et al. 14 and which is a completely different behavior than that observed for DMSO. Water is a polar solvent and, for that reason, it would be expected that it interacts more with the polar part of the sample and a lot less with the hydrophobic aliphatic chains of the cation. According to the molecular dynamics simulation reported in, 14 water has a clear preference for the anion in ionic liquids, which, in this case, is the Cl− . This can be understood in the data by the change of the cross relaxation component of the system, since Cl− is the source of this relaxation mechanism. As observed for the samples containing DMSO-d6, the results obtained for the aged samples do not show the same two cusps and only one cross-relaxation contribution was considered.

18


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The slow rotations/reorientations contributions obtained for the less mobile part of the chain seem to indicate that these local motions become slower in the presence of water, possibly due to an even stronger interdigitation of the carbon chains as a result of their hydrophobic nature (consistent, also, with the smaller value obtained for the intermolecular interspin distance, d). Also, the correlation time increase observed for these slower rotations/ reorientations is much more pronounced for the non-magnetic ionic liquid, which is consistent with water having more affinity with the iron anionic complex than with the chloride anion, thus producing a smaller effect on the motion of the protonated chain of the magnetic ionic liquid. Finally, in Figure 7, are presented the NMR dispersion results obtained at different temperatures for the aged samples of [Aliquat][Cl] and [Aliquat][Cl] / [Aliquat][FeCl4 ] along with the best model fitting curves for the highest and lowest temperatures (see Figure 6 for the model fittings at 25o C). Table 4 contains the respective fitting parameters information. As it can be observed in Figure 7, a) - b), the dispersion profiles obtained at 70o C for the non-magnetic ionic liquid are much more affected by temperature than those of the magnetic system, in spite of the relatively small concentration of [Aliquat][FeCl4 ] added. Across the low frequency range, one of the dominant relaxation mechanism is translational diffusion (see supporting information for separate contributions) and it can be seen in the fitting parameters summary (Table 4) that the introduction of magnetic particles in the system impedes a more pronounced increase in the diffusion coefficient. In addition, for the nonmagnetic ionic liquid, the correlation time related to slower rotations/reorientations is much more affected by the temperature increase than that of the magnetic system (see Table 4). These results suggest that the presence of the iron anionic complex affects the activation energy of the slow rotations, which is lower for the non-magnetic ionic liquid. At 5o C, the consistent analysis of the relaxation rate was possible for all the frequencies only when considering a monoexponential decay of the longitudinal magnetization. These results are summarized in Figure 7, c) - d), together with the model fitting curves. This

19



monoexponential behavior at lower temperatures can be interpreted in terms of an averaging of the T1 values of the two populations due to the spin diffusion. The correlation times of the CH2 and CH3 groups become closer, which favors the description of the spin lattice relaxation by a single relaxation time. This can be interpreted in terms of what could be described as a progressive freezing of the molecular chains conformations (the chains reorient as rigid rods). From the obtained results it is possible to conclude that the super-paramagnetic effect is always present within the temperature range from 5-70o C. Moreover, it is noticeable that this effect is enhanced at lower temperatures, possibly as a consequence of an increased local molecular organization.

Conclusions In this work, the molecular dynamics of [Aliquat]-based ionic liquid mixtures with DMSOd6 was studied through 1 H NMR (relaxometry and diffusometry) and viscometry. The diffusometry and relaxometry results were consistently analyzed, taking into account the effect of the parameters, ∆ and δ, on the diffusion constant obtained value and the model simplifications regarding the existing spin populations and their relative proportions. It was determined that, at low concentrations (1 and 10% (v/v)), DMSO gives rise to more compact ionic aggregates, which is probably the reason why the super-paramagnetic properties of the [Aliquat][Cl] / [Aliquat][FeCl4 ] system were enhanced by the presence of this co-solvent. The effect of the DMSO on the super-paramagnetic properties is, however, not further enhanced when its concentration is changed form 1 to 10%. Therefore, the superparamagnetic properties may be reduced at higher DMSO concentrations, in agreement with previous observations. It was clearly demonstrated that DMSO-d6, in the used concentrations, produces a decrease in the viscosity of the studied MILs without compromising their super-paramagnetic properties. The small profile decrease observed in Figure 6 is not enough

20


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for the conclusions regarding the effect of DMSO-d6 to change and it would be even smaller had the measurements from reference 21 been done at 25 o C - see Figure 7. Moreover, if the measurements had been performed at the same temperature, the differences observed in Figure 1, showing the effect of the addition of DMSO-d6, would be more pronounced - see Figure 7. It was possible to conclude that, neither temperature (in the range 5o C to 70o C) nor the water absorbed by the system over time produced an appreciable effect towards a significant reduction of the super-paramagnetic properties. Nevertheless, it is clear from the results obtained at 5o C that this decrease in temperature produced a slight enhancement of the super-paramagnetic properties and that the increase in temperature up to 70o C produced a reversed effect. It is possible that a further increase of temperature produces a larger reduction or even the suppression of these properties. The fine adjustment of the superparamagnetic properties controlled by the water content is, however, not a real possibility due to the hydrophobicity of the ionic liquids used in this study.

Supporting Information Content In the Supporting Information it is presented a figure (Figure S1) showing the setup used for the viscosity measurements. Figure S2 presents the spectra for the fresh and aged magnetic ionic liquid studied in this work and is followed by Figure S3, which shows the integrals of different regions of the [Aliquat][Cl] spectrum, in order to justify the used population ratio. Table S1 summarizes the model fitting parameters for the aging effect study and Table S2 presents the molar fractions of the mixtures containing DMSO-d6. NMRD curves fitting reports for all the studied samples (and for each temperature), containing the mathematical expression of the fitted model, the associated curve and the value obtained for each parameter, can be consulted on the Supporting Information, as well. In addition, the curves for the separate contributions involved in the theoretical model - rotational diffusion, translational

21



self diffusion, 1 H -

35

Cl cross-relaxation and paramagnetic relaxation - are also available in

the fitting reports.

Acknowledgments The authors acknowledge Funda¸caõ para a Ciência e a Tecnologia (FCT) projects UID/CTM/ 01540/2013, UID/DTP/04138/2013, UID/CTM/50025, and POCI-01-0145-FEDER-007688. This work is also funded by FEDER funds through the COMPETE 2020 Programme. Andreia A. Rosatella thanks FCT project SFRH/BPD/75045/2010. Marta Corvo and Pedro Almeida wish to acknowledge LabNMR-CENIMAT at FCT-UNL and RNRMN for access to the facilities. RNRMN is supported with funds from the Foundation for Science and Technology.

References (1) Kinart, C. M.; Kinart, W. J. Physicochemical Methods Used to Study Internal Structures of Liquid Binary Mixtures. Physics and Chemistry of Liquids 2000, 38, 155–180. (2) Hallett, J. P.; Welton, T. Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2. Chemical Reviews 2011, 111, 3508–3576. (3) van Rantwijk, F.; Sheldon, R. A. Biocatalysis in Ionic Liquids. Chemical Reviews 2007, 107, 2757–2785. (4) Egorova, K. S.; Gordeev, E. G.; Ananikov, V. P. Biological Activity of Ionic Liquids and their Application in Pharmaceutics and Medicine. Chemical Reviews 2017, 117, 7132–7189. (5) Shi, R.; Wang, Y. T. Dual Ionic and Organic Nature of Ionic Liquids. Scientific Reports 2016, 6, 19644. 22


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(6) Li, W. J.; Zhang, Z. F.; Han, B. X.; Hu, S. Q.; Xie, Y.; Yang, G. Y. Effect of Water and Organic Solvents on the Ionic Dissociation of Ionic Liquids. Journal of Physical Chemistry B 2007, 111, 6452–6456. (7) Zhang, Q. G.; Wang, N. N.; Yu, Z. W. The Hydrogen Bonding Interactions Between the Ionic Liquid 1-Ethyl-3-Methylimidazolium Ethyl Sulfate and Water. Journal of Physical Chemistry B 2010, 114, 4747–4754. (8) Cocchi, M.; De Benedetti, P. G.; Seeber, R.; Tassi, L.; Ulrici, A. Development of Quantitative Structure-Property Relationships Using Calculated Descriptors for the Prediction of the Physicochemical Properties (n(D), p, bp, epsilon, eta) of a Series of Organic Solvents. Journal of Chemical Information and Computer Sciences 1999, 39, 1190–1203. (9) Elpidoforou, N.; Skarmoutsos, I.; Kainourgiakis, E.; Raptis, V.; Samios, J. Local Structure and Translational Dynamics of NMF (N-methylformamide)-DMF (N,Ndimethylformamide) Mixtures, Via Molecular Dynamics Simulation. Journal of Molecular Liquids 2017, 226, 16–27. (10) Perez-Pimienta, J. A.; Sathitsuksanoh, N.; Thompson, V. S.; Tran, K.; PonceNoyola, T.; Stavila, V.; Singh, S.; Simmons, B. A. Ternary Ionic Liquid–Water Pretreatment Systems of an Agave Bagasse and Municipal Solid Waste Blend. Biotechnology for Biofuels 2017, 10, 72. (11) Dalai, B.; Dash, S. K.; Singh, S. K.; Swain, B. B. H-1 NMR and Acoustic Response of Binary Mixtures of an Organophosphorous Extractant with 1-Alkanols (C-1-C-4, C-8). Journal of Molecular Liquids 2015, 208, 151–159. (12) Matsugami, M.; Yamamoto, R.; Kumai, T.; Tanaka, M.; Umecky, T.; Takamuku, T. Hydrogen Bonding in Ethanol-Water and Trifluoroethanol-Water Mixtures Studied by

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NMR and Molecular Dynamics Simulation. Journal of Molecular Liquids 2016, 217, 3–11. (13) Stange, P.; Fumino, K.; Ludwig, R. Ion Speciation of Protic Ionic Liquids in Water: Transition from Contact to Solvent-Separated Ion Pairs. Angewandte Chemieinternational Edition 2013, 52, 2990–2994. (14) Zhao, Y.; Wang, J.; Wang, H.; Li, Z.; Liu, X.; Zhang, S. Is There Any Preferential Interaction of Ions of Ionic Liquids with DMSO and H2 O? A Comparative Study from MD Simulation. The Journal of Physical Chemistry B 2015, 119, 6686–6695. (15) Govinda, V.; Attri, P.; Venkatesu, P.; Venkateswarlu, P. Evaluation of Thermophysical Properties of Ionic Liquids with Polar Solvent: A Comparable Study of Two Families of Ionic Liquids with Various Ions. Journal of Physical Chemistry B 2013, 117, 12535– 12548. (16) Liqun Zhang, Z. X., Yong Wang; Li, H. Comparison of the Blue-Shifted C-D Stretching Vibrations for DMSO-d6 in Imidazolium-Based Room Temperature Ionic Liquids and in Water. The Journal of Physical Chemistry B 2009, 113, 5978–5984. (17) Tokuda, H.; Baek, S.; Watanabe, M. Room-Temperature Ionic Liquid-Organic Solvent Mixtures: Conductivity and Ionic Association. Electrochemistry 2005, 73, 620–622. (18) Lee, S. H.; Ha, S. H.; Ha, S.-S.; Jin, H.-B.; You, C.-Y.; Koo, Y.-M. Magnetic Behavior of Mixture of Magnetic Ionic Liquid [bmim]FeCl4 and Water. J. Appl. Phys. 2007, 101, 09J102. (19) de Pedro, I.; Rojas, D. P.; Albo, J.; Luis, P.; Irabien, A.; Blanco, J. A.; Rodriguez Fernandez, J. Long-Range Magnetic Ordering in Magnetic Ionic Liquid: Emim[FeCl4]. Journal of Physics-condensed Matter 2010, 22, 296006.

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(20) de Pedro, I.; Rojas, D. P.; Blanco, J. A.; Rodriguez Fernandez, J. Antiferromagnetic Ordering in Magnetic Ionic Liquid Emim[FeCl4]. Journal of Magnetism and Magnetic Materials 2011, 323, 1254. (21) Daniel, C. I.; Chávez, F. V.; Feio, G.; Portugal, C. A.; Crespo, J. G.; Sebastião, P. J. 1 H NMR Relaxometry, Viscometry and PFG NMR Studies of Magnetic and Nonmagnetic Ionic Liquids. The Journal of Physical Chemistry B 2013, 117, 11877–11884. (22) Daniel, C. I.; Chávez, F. V.; Portugal, C. A.; Crespo, J. G.; Sebastião, P. J. 1 H NMR Relaxation Study of a Magnetic Ionic Liquid as a Potential Contrast Agent. The Journal of Physical Chemistry B 2015, 119, 11740–11747. (23) Del Sesto, R. E.; McCleskey, T. M.; Burrell, A. K.; Baker, G. A.; Thompson, J. D.; Scott, B. L.; Wilkes, J. S.; Williams, P. Structure and Magnetic Behavior of Transition Metal Based Ionic Liquids. Chem. Comm. 2008, 447–449. (24) Scovazzo, P.; Portugal, C. A.; Rosatella, A. A.; Afonso, C. A.; Crespo, J. G. Hydraulic Pressures Generated in Magnetic Ionic Liquids by Paramagnetic Fluid/Air Interfaces Inside of Uniform Tangential Magnetic Fields. Journal of Colloid and Interface Science 2014, 428, 16 – 23. (25) Tao, R.; Xu, X. Reducing the Viscosity of Crude Oil by Pulsed Electric or Magnetic Field. Energy & Fuels 2006, 20, 2046–2051. (26) Sousa, D.; Domingos Marques, G.; Cascais, J. M.; Sebastião, P. J. Desktop Fast-Field Cycling Nuclear Magnetic Resonance Relaxometer. Solid State NMR 2010, 38, 36–43. (27) Price, W. S. Pulsed-Field Gradient Nuclear Magnetic Resonance as a Tool for Studying Translational Diffusion .1. Basic Theory. Concepts In Magnetic Resonance 1997, 9, 299–336.

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(28) Brito, L. M.; Sebastião, P. J.; Tavares, M. I. B. NMR Relaxometry Evaluation of Nanostructured Starch-PLA Blends. Polymer testing 2015, 45, 161–167. (29) Bloembergen, N.; Purcell, E. M.; Pound, R. V. Relaxation Effect in Nuclear Magnetic Resonance Absorption. Physical Review 1948, 73, 679–712. (30) Torrey, H. C. Nuclear Spin Relaxation by Translational Diffusion. Physical Review 1953, 92, 962–969. (31) Sebastião, P. J. O. Estudo da Dinâmica Molecular em Cristais L´ıquidos com Polimorfismos Peculiares. Ph.D. thesis, Instituto Superior Técnico - Universidade de Lisboa, 1993. (32) Anoardo, E.; Pusiol, D. J.; Aguilera, C. NMR Study of the T1 Relaxation Dispersion in the Smectic Mesophase of 4 – Chlorophenyl 4 – Undecyloxybenzoate. Physical Review B 1994, 49, 8600–8607. (33) Gillis, P.; Roch, A.; Brooks, R. A. Corrected Equations for Susceptibility-Induced T2 – Shortening. Journal of Magnetic Resonance 1999, 137, 402–407. (34) Roch, A.; Muller, R. N.; Gillis, P. Theory of Proton Relaxation Induced by Superparamagnetic Particles. J. Chem. Phys. 1999, 110, 5403–5411. (35) Sebastião, P. J. The Art of Model Fitting to Experimental Results. European Journal of Physics 2014, 35, 015017. (36) Radhi, A.; Le, K. A.; Ries, M. E.; Budtova, T. Macroscopic and Microscopic Study of 1- Ethyl-3-methyl-imidazolium Acetate – DMSO Mixtures. The Journal of Physical Chemistry B 2015, 119, 1633–1640. capitalization

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Table 2: Viscosity and diffusion constant results obtained for the studied samples at 25o C. The estimated uncertainty of the viscosity was 0.003 Pa · s. The estimated relative uncertainty of the diffusion constant was 10%. (*) Values reported by Daniel et al. 21 .“aged” refers to new values obtained for aged samples. ViscosityViscosity Diffusion at at Constant B = 0T B = 2T at B = 7T (Pa · s) (Pa · s) (10−12 m2 /s)

IL

1.33* –

[Aliquat][Cl]

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ]

1.26* –


1.17* –

0.938

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ] / 0.923 (1% v/v) DMSO-d6 [Aliquat][Cl] / (10% v/v) DMSO-d6

0.916

0.231

[Aliquat][Cl] / (1% v/v) [Aliquat][FeCl4 ] / 0.238 (10% v/v) DMSO-d6

27

0.227


1.4* aged: 1.6

4.7* aged: 6.9

1.2

10.8

3.4

22.2


10

3

10

3

2

10

2

-1

R1,CH3(s )

10

b)

-1

R1,CH3(s )

a)

10

1

10

1

[Aliquat][Cl] + 1% [Aliquat][FeCl4] + 1% DMSO-d6 [Aliquat][Cl] + 1% [Aliquat][FeCl4] [Aliquat][Cl] + 1% [Aliquat][FeCl4] + 10% DMSO-d6

10

10

[Aliquat][Cl] + 1% DMSO-d6 [Aliquat][Cl] [Aliquat][Cl] + 10% DMSO-d6

0

10

4

5

6

7

10 10 10 10 1 H Larmor Frequency (Hz)

10

8

3

10

0

10

4

6

7

8

7

8

d)

10

2

-1

R1,CH2(s )

2

-1

10

5


3

c)

R1,CH2(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 36

10

1

10

1

[Aliquat][Cl] + 1% [Aliquat][FeCl4] + 1% DMSO-d6 [Aliquat][Cl] + 1% [Aliquat][FeCl4] [Aliquat][Cl] + 1% [Aliquat][FeCl4] + 10% DMSO-d6

10

[Aliquat][Cl] + 1% DMSO-d6 [Aliquat][Cl] [Aliquat][Cl] + 10% DMSO-d6

0

10

4

5

6

7


10

8

0

10

4

5

6


Figure 1: Experimental relaxometry results obtained for the samples comprising either [Aliquat][Cl] or [Aliquat][Cl] + [Aliquat][FeCl4 ] and 1 or 10% (v/v) of DMSO-d6 at 25o C. Note that the [Aliquat][FeCl4 ] is always at 1% (v/v) concentration and that the blue squares represent the experimental data obtained by Daniel et al. 21 in the absence of DMSO-d6 at 22 o C.

28


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Figure 2: [Aliquat]+ cation representation obtained after running an energy minimization routine using the software Avogadro (with Van der Waals spheres: white for hydrogen, black for carbon and blue for nitrogen atoms).

Figure 3: 1 H NMR spectra of the [Aliquat][Cl] studied by Daniel et al. 21 and of the new samples comprising the same IL mixed with 1% and 10% (v/v) of DMSO-d6 at 25o C.

29



10

3

10

a)

b)

2

10

Aged [Aliquat][Cl]

2

-1

R1,CH2(s )

10

3

Aged [Aliquat][Cl] + 1%[Aliquat][FeCl4]

-1

R1,CH2(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 36

10

1

10

1

o

o

5C o 25 C o 70 C

10

5C o 25 C o 70 C

0

10

4

5

6

7


10

8

0

10

4

5

6

7


8

Figure 4: Experimental relaxometry results obtained for the less mobile spin population of the aged magnetic and non-magnetic samples at 5, 25 and 70 o C.

30


Page 31 of 36

a)

10

[Aliquat][Cl] +1%[Aliquat][FeCl4] +10%DMSO-d6

2

-1

10

3

R1,CH3(s )

-1

R1,CH3(s )

10

SD

10

1

10

3

[Aliquat][Cl] +10%DMSO-d6

2

10

PM

b)

1 SD

Rot1

-1

10

0

10

4

3

5

6

7


c)

10

[Aliquat][Cl] +1%[Aliquat][FeCl4] +10%DMSO-d6

2 PM

Rot2

SD

10

10

1

10

8

-1

10

Rot1

CR

R1,CH2(s )

10

R1,CH2(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CR

Rot1

4

5

6

10

7


5

6

7


d)

8

[Aliquat][Cl] +10%DMSO-d6

2 Rot2

SD

10

8

4

3

10

0

10

10

CR

0

1

CR

Rot1

0

10

4

5

6

7


8

Figure 5: Experimental and model fitting results obtained for the samples comprising either [Aliquat][Cl] or [Aliquat][Cl] + [Aliquat][FeCl4 ] and a 10% (v/v) concentration of DMSO-d6 at 25o C.

31



Page 32 of 36

Table 3: Results obtained from the best model fits to the experimental 1 H NMRD profiles (25 o C) of the [Aliquat] -based samples mixed with DMSO-d6 along with those related to the new analysis of the data reported in reference [21] (22 o C). The parameters’ uncertainties were estimated as explained in the text. [Aliquat][Cl] [Aliquat][Cl] [Aliquat][Cl] [Aliquat][Cl] /1% (v/v) [Aliquat][Cl] /1% (v/v) [Aliquat][Cl] /1% (v/v) /1% (v/v) [Aliquat][FeCl4 ] /10% (v/v) [Aliquat][FeCl4 ] [Aliquat][FeCl4 ] DMSO-d6 /1% (v/v) DMSO-d6 /10% (v/v) DMSO-d6 DMSO-d6

Model Fitting Parameters

CH2 – 13.8 ± 0.8 CH3 CH2 τv2 (10−9 s ) – 1.4 ± 0.5 CH3 CH2 p2 – 1.6 ± 0.4 CH3 CH2 S – 410 ± 40 CH3 p CH2 1.36 ± 0.06 hr2 i(10−10 m) CH3 2.2 ± 0.3 CH 2 D7T (10−12 m2 s−1 ) 1.80 ± 0.06 6.5 ± 0.2 CH3 CH2 d(10−10 m) 7.4 ± 0.1 CH3 CH2 ARot1 (109 s−2 ) 3.3 ± 0.6 CH3 CH2 6±1 τRot1 (10−10 s) CH3 2.2 ± 0.2 CH 3.1 ± 0.9 2 ARot2 (108 s−2 ) CH3 – CH2 5±2 6±3 τRot2 (10−8 s) CH3 – CH2 26 ± 2 ACR (107 s−2 ) CH3 1.5 ± 0.5 CH ∼ 10 2 τCR (10−8 s) CH3 9±3 CH2 1.5 ± 0.3 fCR (107 Hz−1 ) CH3 1.86 ± 0.06 CH2 2±1 ACR1 (107 s−2 ) CH3 2.5 ± 0.4 CH 25 ± 13 2 τCR1 (10−8 s) CH3 18 ± 3 CH2 3.3 ± 0.1 fCR1 (107 Hz−1 ) CH3 3.3 ± 0.2 τs (10−11 s)

–

7.3 ± 0.8

–

6.9 ± 0.8

–

1.8 ± 0.5

–

1.2 ± 0.5

–

1.4 ± 0.4

–

1.7 ± 0.4

–

479 ± 40

–

434 ± 40

1.11 ± 0.06 2.1 ± 0.3

1.07 ± 0.06 2.0 ± 0.3

1.42 ± 0.05

10.8 ± 0.3

4.1 ± 0.1

12.0 ± 0.4

4.6 ± 0.1 7.4 ± 0.1

4.6 ± 0.1

4.2 ± 0.1 7.1 ± 0.1

4.2 ± 0.1

3.7 ± 0.6 5±1 1.1 ± 0.2 2.6 ± 0.9 – 8±2 4±3 – 13 ± 1 15.3 ± 0.9 11 ± 2 ∼2 1.8 ± 0.3 1.8 ± 0.4

3.7 ± 0.6 5±1 1.1 ± 0.2 1.4 ± 0.9 – 7±2 9±3 – 20 ± 2 9.2 ± 0.8 8±1 ∼2 1.3 ± 0.3 2.6 ± 0.7

–

–

Fixed Parameters 28

−3

nIL (10 spins m ) [M ] (mol L−1 )

7.08

8.25

7.01

0.012

8.20 0.0144

32


6.37

7.40 0.0147

Page 33 of 36

10

3

10

3

a)

2

10

2

-1

-1

R1(s )

10

b)

R1(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10

10

1

10

[Aliquat][Cl] + 1% [Aliquat][FeCl4], CH2 Aged [Aliquat][Cl] + 1% [Aliquat][FeCl4], CH2 [Aliquat][Cl] + 1% [Aliquat][FeCl4], CH3 Aged [Aliquat][Cl] + 1% [Aliquat][FeCl4], CH3

0

10

4

5

6

7


10

8

1 [Aliquat][Cl], CH2 Aged [Aliquat][Cl], CH2 [Aliquat][Cl], CH3 Aged [Aliquat][Cl], CH3

0

10

4

5

6

7


8

Figure 6: Experimental and model fitting results obtained for the aged [Aliquat][Cl] and for the aged mixture of [Aliquat][Cl] with 1% (v/v) of [Aliquat][FeCl4 ] at 25o C along with the results obtained by Daniel et al. 21 for the fresh samples at 22 o C.

33



10

3

10

a)

b)

2

10

10

1

Aged [Aliquat][Cl]

2

-1

R1(s )

-1

R1(s )

10

3


10

1

o

10

o

25 C, CH2

0

o

10

70 C, CH2

25 C, CH2

0

o

70 C, CH2

o

o

25 C, CH3

25 C, CH3

o

o

70 C, CH3

10

70 C, CH3

-1

10

10

4

5

7

10

8

3

-1

10

c)

10

4

5

d)

10

7

8

7

8

3


2

6

10 10 10 10 1 H Larmor Frequency (Hz) Aged [Aliquat][Cl]

2

-1

-1

R1(s )

10

6


R1(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 36

10

1

10

o

25 C, CH2

1 o

25 C, CH2

o

o

5C o 25 C, CH3

10

5C o 25 C, CH3

0

10

4

5

6

7


10

8

0

10

4

5

6


Figure 7: Experimental results obtained for the aged [Aliquat][Cl] and for the aged [Aliquat][Cl] + 1% (v/v) [Aliquat][FeCl4 ] at 5, 25 and 70 o C along with the model fitting curves for the highest and lowest temperatures.

34


Page 35 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 4: Results obtained from the best model fitting to the experimental 1 H NMRD profiles of the aged [Aliquat] -based samples obtained at 5 o C, 25 o C and 70 o C - these NMRD profiles can be observed in Figure 7 of the main manuscript. 5 oC

25 o C

70 o C

Aged Aged Aged Aged [Aliquat][Cl] Aged [Aliquat][Cl] Aged [Aliquat][Cl] [Aliquat][Cl] /1% (v/v) [Aliquat][Cl] /1% (v/v) [Aliquat][Cl] /1% (v/v) [Aliquat][FeCl4 ] [Aliquat][FeCl4 ] [Aliquat][FeCl4 ]

Model Fitting Parameters

CH2 2±1 – CH3 – CH2 τv2 (10−9 s ) – CH3 CH2 p2 – CH3 CH2 434 ± 40 S – CH3 – p CH2 1.56 ± 0.06 hr2 i(10−10 m) CH3 – CH 0.10 ± 0.05 0.54 ± 0.02 2 D7T (10−12 m2 s−1 ) CH3 – D7T (10−12 m2 s−1 )CH2 – PFG 1 H NMR CH3 CH2 4.6 ± 0.1 d(10−10 m) CH3 – CH2 2.5 ± 0.6 ARot1 (109 s−2 ) CH3 – CH 11 ±1 2 τRot1 (10−10 s) CH3 – CH2 ∼ 0.3 ARot2 (108 s−2 ) CH3 – CH2 23 ± 3 25 ± 4 τRot2 (10−8 s) CH3 – CH2 9.5 ± 0.1 ACR (107 s−2 ) CH3 – CH 11 ±3 2 τCR (10−8 s) CH3 – CH2 1.4 ± 0.3 fCR (107 Hz−1 ) CH3 – τs (10−11 s)

–

12.4 ± 0.8

–

16.5 ± 0.8

–

1.2 ± 0.5

–

∼ 0.6

–

2.0 ± 0.4

–

2.4 ± 0.4

–

402 ± 40

–

359 ± 40

1.40 ± 0.06 2.3 ± 0.3

1.32 ± 0.06 2.4 ± 0.3

2.8 ± 0.1

11.5 ± 0.4

29.1 ± 0.5

11.7 ± 0.2

1.62 ± 0.07

6.9 ± 1.6

41 ± 14

–

7.0 ± 0.1

6.5 ± 0.1

3.7 ± 0.6

2.9 ± 0.6

6±1 1.1 ± 0.2 1.3 ± 0.9 – 10 ± 2 9±3 – 24 ± 1 8.4 ± 0.7 10.3 ± 0.9 ∼3 1.0 ± 0.3 2.2 ± 0.5

4±1 0.5 ± 0.2 1.1 ± 0.9 – ∼3 5±3 – 4.6 ± 0.3 ∼ 0.1 12 ± 1 12 ± 5 1.8 ± 0.3 1.9 ± 0.4

Fixed Parameters 28

−3

nIL (10 spins m ) [M ] (M ol L−1 )

7.08

8.25

7.08

0.012

8.25 0.012

35


7.08

8.25 0.012


10

3

MIL+DMSO MIL

10

2

MIL+H2O

-1

R1(s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 36

IL

10

1 IL: [Aliquat][Cl] MIL: [Aliquat][Cl] + 1% [Aliquat][FeCl4]

10

0

10

4

5

6

7


TOC Graphic

36


8

1H NMR Relaxometry and Diffusometry Study of Magnetic and

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