INTERMOLECULAR INTERACTION STUDIES AND ...joics.org/gallery/ics-2091.pdfvelocity and viscosity measurement [2-8]. Intermolecular interactions and thermodynamic properties of ionic

INTERMOLECULAR INTERACTION STUDIES AND SPECTRAL

ANALYSIS OF SPECIFIC BINDING SITES BETWEEN

IMIDAZOLIUM HALIDES AND POLAR- PROTIC SOLVENT

Seethalakshmi.K

PG & Research Department of Physics, Seethalakshmi Ramaswami College,

Tiruchirappalli-2, Tamilnadu, India

Mail id: [email protected]

Abstract

Ultrasonic technique is the vital probe in evaluating the thermo-dynamical parameters

such as internal pressure and free volume. In the present investigation, non-aqueous solutions of

the selected ionic liquid, 1-alkyl-3-methylimidazolium chloride and bromide have been prepared

with various concentrations and the experiments were carried out to measure ultrasonic velocity,

density, viscosity from 5°C to 55°C. Using these experimental data, the acoustical parameter i.e.,

intermolecular free length are determined to reveal the nature and strength of the interactions

taking place in the solution. These experimental values have been analyzed and eventually

emphasizing the possible molecular interactions. Solute–solvent interactions are conveniently

studied by several spectroscopic techniques. IR spectra find wide spread applications for the

qualitative and quantitative analysis of compounds and this technique is also well employed

in the field of research to understand the nature of inter atomic bonding. In the present study,

FT-IR spectra are recorded for 1-alkyl-3-methylimidazolium chloride and bromide, its solution

in polar-protic solvent in the wave number region from 4000 cm-1 to 400 cm-1. The spectra are

used to assign various stretching and bending modes of vibrations of the samples and also to

identify the various phases present in the samples. A comparative study is made between the

observed frequencies of the pure solvent and the solutions. From this evaluation, the shifts in

frequencies are corroborated. These shifts in the solution are ascribed to strong solute-solvent

interaction by specific bonding between NH2 and C=O of solvent to Cl- ,Br- and +NCH3 in the

imidazolium chloride and bromide.

Keywords: Ionic liquid, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium

bromide, vibrational frequencies.

Journal of Information and Computational Science

Volume 9 Issue 12 - 2019

ISSN: 1548-7741

www.joics.org1522

mailto:[email protected]

1. Introduction

Study of molecular interactions between solute and solvent media has got great

importance in many field of science including medicinal chemistry, industrial processes,

biochemistry, etc. The structure making and structure breaking properties of solute can be

studied by measuring viscosity and ultrasonic velocity of a sample in the solution [1]. Literature

survey shows that many researchers have studied the molecular interactions by ultrasonic

velocity and viscosity measurement [2-8]. Intermolecular interactions and thermodynamic

properties of ionic liquids can be estimated more precisely using ultrasonic technique [9-10]. An

ionic liquid typically consists of organic nitrogen-containing heterocylic cations and inorganic

anions. Hence in the present investigation, solution of 1-ethyl-3-methylimidazolium chloride and

bromide in formamide are analyzed for the specific bonding and interactions using FT-IR and

FT-Raman spectral results. This emimCl can be used in cellulose processing [11,12]. It has good

electrical conductivity, high ionic mobility, and excellent chemical stabilities. It is also used in

electro chemical devices, as Li rechargeable batteries. The aqueous solutions of emimBr can be

accounted for in terms of the hydrophobic hydration of ions and that this IL exhibits columbic

interactions as well as hydrophobic hydration for both the cations and anions[13].

2. Experimental technique

1-ethyl-3-methylimidazolium chloride (emimCl), 1-ethyl-3-methylimidazolium bromide

(emimBr) and formamide (99% purity AR Merck) were used as such. The spectra are recorded

at Sophisticated Analytical Instruments Facility (SAIF), IIT Madras. The IR spectroscopy is also

carried out by using Fourier transform technique. The FT-IR spectra of the compounds are

recorded using PERKIN ELMER SPECTRUM ONE FTIR Spectrometer with a scan range MIR

4000-400 cm-1.This instrument has a typical resolution of 1.0 cm-1. The FT-RAMAN spectra,

using BRUKER RFS 27 spectrometer with 100 mw power with scan range 4000 - 50 cm-1.

3. Results and Discussion

3.(i) Internal Pressure (πi) and Free Volume (Vf)

Internal pressure and free volume are the thermodynamical properties which explain the

interaction in the solution. Internal pressure is a single factor that appears to vary due to all the

intermolecular interactions. Internal pressure plays an important role in explaining molecular

interaction, as this represents the resultant of the forces of attraction and repulsion between the

molecules.

Free volume is the average volume in which the center of the molecule can move inside

the hypothetical cell due to the repulsion of surrounding molecules. Study of these parameters

requires ultrasonic velocity, viscosity and density.

The significance of internal pressure and its correlation with the solubility parameter has

been discussed in review articles by Barton[14] and independently by Dack[15].



ISSN: 1548-7741

www.joics.org1523

http://en.wikipedia.org/wiki/Cellulose

http://en.wikipedia.org/wiki/1-Ethyl-3-methylimidazolium_chloride#cite_note-1

http://en.wikipedia.org/wiki/1-Ethyl-3-methylimidazolium_chloride#cite_note-1

The variations of internal pressure and free volume with temperature and molalities are

shown in figures 3.1 – 3.4. In the present study, the internal pressure shows an increasing trend

only at higher molalities in all temperatures. This suggests that there is a strong solute – solvent

interaction due to high cohesive energy. This may be due to the hydrogen bonding. This

emphasizes that the addition of salt in the solvent behaves as a structure maker. From the figure

(3.1), it is observed for emimCl, the internal pressure increases with concentration. But there is a

slight decrease appears, when the concentration increases (0.1m) at lower temperatures (5°C ,

15°C) (Table 3.1) In emimCl, free volume is found to be decreasing with respect to temperature

and decreasing with respect to concentration as expected. This result confirms the strong – solute

solvent interaction in emimCl solution.[16].

In the case of emimBr, the internal pressure increases with concentration (Table 3.2 and

Fig 3.2). It exhibits a structure stabilizing nature. However, a dip in the increasing values of

internal pressure with concentration is observed at (0.01m at 5°C,25°C – 55°C) and (0.005m at

15°C). This may be due to weakening of interactions at specific concentrations and temperature

suggesting the loosening of structures due to lowering of cohesive energy. As the temperature

increases, the internal pressure decreases. The decreasing values of free volume with molalities

and the change or the increase in free volume in its decreasing trend is in agreement with the

structure making/breaking behavior of the solutes.

INTERNAL PRESSURE (atms)

Figure 3.1: 1-ETHYL-3-METHYLIMIDAZOLIUM CHLORIDE

Figure 3.2: 1-ETHYL-3-METHYLIMIDAZOLIUM BROMIDE

8000

10000

12000

14000

16000

18000

20000

0.001 0.005 0.01 0.05 0.1

Inte

rnal

P

ress

ure

(atm

s)

Molality(m)

5˚C

15˚C

25˚C

35˚C

45˚C



ISSN: 1548-7741

www.joics.org1524

TABLE-3.1: 1-ETHYL-3-METHYLIMIDAZOLIUM CHLORIDE

Molality(m) 5˚C 15˚C 25˚C 35˚C 45˚C 55˚C

0.001 18685 16020 13750 13073 11578 10207

0.005 19329 16340 13876 13207 11781 10621

0.01 19501 16464 13955 13276 11873 10642

0.05 19689 16655 14158 13155 12027 10753

0.1 18339 15220 14036 12363 11533 10736

TABLE-3.2: 1-ETHYL-3-METHYLIMIDAZOLIUM BROMIDE

FREE VOLUME (cc)


10000

12000

14000

16000

18000

20000

22000

0.001 0.005 0.01 0.015 0.02In

tern

al

Pre

ssu

re(a

tms)

Molality(m)

5˚C15˚C25˚C35˚C45˚C55˚C

0

0.02

0.04

0.06

0.08

0.1

0.001 0.005 0.01 0.015 0.02

Fre

eV

olu

me

(cc)

Molality(m)

5˚C15˚C25˚C35˚C45˚C55˚C


0.001 20259 16887 14385 13199 12150 11053

0.005 19593 17035 14450 13591 12042 11176

0.01 20547 16920 14635 13597 12087 11295

0.015 20647 17178 14658 13188 12341 11357

0.02 20425 17098 14313 13476 12153 11349



ISSN: 1548-7741

www.joics.org1525




0.001 0.009423 0.0164 0.028328 0.03602 0.056278 0.088861

0.005 0.008517 0.015503 0.027765 0.034948 0.053373 0.078759

0.01 0.008287 0.015153 0.02717 0.034423 0.052166 0.078295

0.05 0.007974 0.014538 0.025862 0.035146 0.04979 0.075298

0.1 0.009761 0.018801 0.026285 0.041781 0.056004 0.074865


3.(ii) Intermolecular free length (Lf)

The intermolecular free length (Lf) is the distance between the surfaces of the

neighboring molecules[17]. The variation in intermolecular free length indicates that there are

interactions between solute and solvent molecules due to which the structural arrangement in the

neighborhood of constituent ions or molecules gets affected considerably.

The intermolecular free length increases with rise in temperature. The intermolecular free

length with molality is given in tables 3.5 and 3.6 (figures 3.5 and 3.6).

In the case of emimCl, there exists rise and fall in free length. A dip in free length is

observed at (0.01m) which indicates that there is a strong solute – solvent interaction. The

intermolecular free length in emimBr increases with concentration and temperature.

0

0.02

0.04

0.06

0.08

0.1

0.001 0.005 0.01 0.015 0.02Fr

ee

Vo

lum

e(c

c)

Molality(m)

5˚C15˚C25˚C35˚C45˚C55˚C


0.001 0.007385 0.014109 0.024936 0.034967 0.048675 0.069548

0.005 0.008179 0.013674 0.024461 0.031879 0.049892 0.067456

0.01 0.007083 0.013911 0.023571 0.031942 0.049288 0.065405

0.015 0.006971 0.013354 0.023461 0.034816 0.046228 0.064154

0.02 0.007159 0.013462 0.025134 0.032675 0.048301 0.06435



ISSN: 1548-7741

www.joics.org1526

INTERMOLECULAR FREE LENGTH (Å)


0.1000

0.1100

0.1200

0.1300

0.001 0.005 0.01 0.05 0.1Inte

rmo

lecu

lar

fre

e

len

gth

(À)

Molality(m)

5°C15°C25°C35°C45°C


0.1000

0.1100

0.1200

0.1300

0.001 0.005 0.01 0.015 0.02

Inte

rmol

ecul

ar fr

ee

leng

th(À

)

Molality(m)

5°C15°C25°C35°C45°C55°C



0.001 0.10872 0.11169 0.11614 0.11761 0.11990 0.12185

0.005 0.10895 0.11186 0.11619 0.11729 0.12068 0.12321

0.01 0.10832 0.11101 0.11514 0.11652 0.11930 0.12135

0.015 0.10898 0.11179 0.11624 0.11808 0.12154 0.12310

0.02 0.10901 0.11244 0.11594 0.11774 0.11912 0.12137



0.001 0.10643 0.11080 0.11500 0.12000 0.12440 0.12779

0.005 0.10759 0.11200 0.11600 0.12040 0.12340 0.12719

0.01 0.10759 0.11150 0.11600 0.11940 0.12300 0.12776

0.015 0.10714 0.11180 0.11600 0.11890 0.12360 0.12837

0.02 0.10703 0.11120 0.11600 0.11930 0.12380 0.12703

3.(iii) FT-IR Spectral analysis of 1–ethyl–3–methylimidazolium chloride in formamide

In the solution spectra, as the dilution increases the broad peak shifts from 3419 cm–1 to

3417 cm–1(Fig 3.7) This blue shift of the N–H peak indicates lengthening of the NH bond due to



ISSN: 1548-7741

www.joics.org1527

the H–bonding between solute and solvent. The C Ostretching frequency of formamide

found at 1694 cm–1 has not undergone much shift on dilution, there by indicating absence of H–

bonding between imidazole and C O group of the solvent..

The characteristic ring bending vibration of imidazole ring found at 622 cm–1 has

undergone a blue shift from 608 to 603 cm–1 on dilution. This shift is indicative of strong

solvation in formamide.

The focus has been on the CH–stretching region of the imidazolium ring, which is

supposed to carry information about a possible hydrogen bonding network in the ionic

liquid[18].

Fig 3.7 FT-IR spectrum – 1-ethyl-3-methylimidazolium Chloride solution

3.(iv) FT-Raman Spectral analysis of 1–ethyl–3–methylimidazolium chloride in formamide

In the case of emimCl solution, at saturation molality, even though several peaks occur

in these concentration the 2887 cm–1 peak characteristic of C N , stretching mode indicates the

dilution effect and reflects strong solute–solvent interactions. (Fig 3.8) A significant shift (9 cm–

1) is observed in the C–O region of the Raman spectra at 1092 cm–1 for this concentration,

besides the shift of the electronic band from 1309 cm–1 in the pure solvent to 1310 cm–1

(saturation molality). The oscillation resonance behavior of this peak is indicative of the solute

interacting with dipoles of the solvent formamide. .

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0 0.0

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

100.0

cm-1

%T

3419

2887

2770

2198

1694 1391

1312

1171

1051

608



ISSN: 1548-7741

www.joics.org1528

Fig 3.8 Raman spectrum – 1-ethyl-3-methylimidazolium chloride solution

3.(v) FT-IR Spectral analysis of 1–ethyl–3–methylimidazolium bromide in formamide

In the solution spectra, (Fig 3.9), these bands are absent but a broad band due to solute–

solvent interaction is observed. The νC= N+

Me band at 2690 cm–1 in the solid state has undergone a

red shift to 2701 cm–1 in solution, predicting a strong solute–solvent interaction at this cationic

site. The C O group vibration in formamide (νCO 1685 cm–1) has shifted to 1694 cm–1 due to

this cationic binding. The C Ostretching vibration at 1051 cm–1 is not significantly affected

indicating that the interaction between the CO of formamide and CH3+ N=C of imidazolium ion

are of ion dipole interaction.

The characteristic solute peaks in emimBr salt exhibit the following stretching

vibrations in the infrared spectrum 3409 cm–1, 3149 cm–1and 3093 cm–1 for test nitrogen 2416

cm–1 and 2063 cm–1 for C N . The νCH vibrations are at 2986 cm–1, 2876 cm–1 and 2690

cm–1.The bands at 1388 cm–1 and 1336 cm–1 νasymmetric and νsymmetric stretch for C N group of

emimBr. These vibrations are characteristics of electron delocalization at this site. The νCO

vibration of the solvent at 1685 cm–1 has shifted to 1681 cm–1. All these results indicate that inter

molecular binding occurs through the tertiary N atom.



ISSN: 1548-7741

www.joics.org1529

Fig.3.9 FT-IR spectrum – 1-ethyl-3-methylimidazolium Bromide solution

3.(vi)FT-Raman Spectral analysis of 1–ethyl–3–methylimidazolium bromide in formamide

The Raman active band at 1565 cm–1 in the solid has undergone a red shift to 1593 cm–1

and in the solutions confirming the ion–dipole interaction between imidazolium cation and

formamide. (Fig 3.10)

Fig.3.10 Raman spectrum – 1-ethyl-3-methylimidazolium Bromide solution

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0 0.0

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

100.0

cm-1

%T

3422

2891

2770

2702 2191

1685

1456

1390 1314

1170

1087

1052

607



ISSN: 1548-7741

www.joics.org1530

Conclusion

Acoustics and spectroscopy are found to be the two important fields to study the

molecular interactions in the liquid system.

The fundamental nature of the internal pressure and free volume in determining the

interactions in the systems and hence the behavior of solutions has been well established.

i.e., temperature, internal pressure and free volume are the three basic thermodynamic

properties of the liquid systems similar to temperature, pressure and volume for gaseous

systems. The existence of ion-solvent (or) solvent – solvent interaction resulting in

attractive forces promote the structure – making tendency/enhancing nature of solute

behavior is observed in the samples

From FT-IR spectral analysis, strong solute-solvent interaction occurs in the non-aqueous

solution of formamide and emimCl. A chloride ion bridge exists between solute and the

solvent molecule.

In the spectral study of emimBr solution, the intermolecular binding between solute and

solute is formed through the tertiary N–atom. These results indicate that bromide salts do

not break the solvent. This confirms that ion-ion or solute – solute interaction resulting

dipole-dipole, dipole induced dipole and electrostrictive forces, strengthen the structure.

It is observed that the imidazolium salts forms H–bonds with formamide and the results

confirm that the 1–alkyl–3–methylimidazolium Chloride forms strong H–bonds with

formamide than the 1–alkyl–3–methylimidazolium Bromide.

FT-Raman spectroscopic study confirms the ion–dipole interaction between imidazolium

cation and formamide.

References

1. S. D. Deoskarkar,M, M. L. Narwade, Rasayan J. Chem., 2010,3(1), 55-59

2. V. D. Bhandakar, O.P. Chimankar and N. R. Pawar, J. Chem. Pharm. Res., 2010, 2(4), 873-

877

3. P. S. Agrawal , M. S. Wagh, L. J. Paliwal, Archives of Applied Science Research, 2011, 3(2),

29-33

4. P. Kumar, S. Jayakumar, V. Kannappan, Indian Journal of Applied Physics,

5. A. N. Sonar and N. S. Pawar, Rasayan J. Chem., 2010, 3(1), 38-43

6. R.Ezhil Pavai and S. Renuka, International Journal of Research in Pure and applied Physics,

2011, 1(2), 6-10



ISSN: 1548-7741

www.joics.org1531

7. Anjana and Rajinder Bamezai, Archives of Applied Science Research, 2011, 3(1), 370-379

8. P. Vasantharani, L. Balu, R. Ezhil Pavai and S. Shailajha, Global Journal of Molecular

Sciences, 2009, 4(1), 42-48

9. S.Jayakumar, N.Karunanithi and V.Kamappan, Indian J Pure Appl PHY.34 (1996)761.

10. S.K.Dash,V.Chakravorthy and B.B.Swain,Acoust Leto 19(1996) 142.

11.“Scientists Propose a More Efficient Way to Make Ethanol”, The New York Times (2010).

12.Joseph B, Binder and Ronald T. Raines PNAS 107 (10) (2010) pp 4516 –4521.

13.The journal of chemical Physics 135,074505 (2011).

14.Barton A.F.M, Chem.Rev.,75(6) (1975) pp 731 – 753.

15.Dack M R J, Chem soc Rev (London), 49 (1975) 211.

16.Kannappen V, Xavier Jesu Raja S and Jaya Santhi R, Indian J Pure and Appl Phys, 41 (2003)

690.

17.Palani R, Balakrishnan S, Sudhamani A, ARPNJ. of Eng. And Appl. Phys. 5(12), (2010) pp 58

– 64.

18.Roth C, Chatzipapadopoulos S, Kerlé D, Friedriszik F, Lütgens M, Lochbrunner S, Kühn

O and Ludwig R ,New J. Phys. 14 (2012).



ISSN: 1548-7741

www.joics.org1532

Documents

INTERMOLECULAR INTERACTION STUDIES AND ...joics.org/gallery/ics-2091.pdfvelocity and viscosity measurement [2-8]. Intermolecular interactions and thermodynamic properties of ionic