DOI 10.1007/s11182-015-0391-2 Russian Physics Journal, Vol. 57, No. 10, February, 2015 (Russian Original No. 10, October, 2014)

SUPRAMOLECULAR STRUCTURE OF 1,3-DIMETHYL-2IMIDAZOLIDINONE FROM THE DATA OF FOURIER TRANSFORM RAMAN SPECTROSCOPY V. V. Lazarev, M. T. Hatmullina, and G. P. Michailov

UDC 535.375; 532.74

The supramolecular structure of 1,3-dimethyl-2-imidazolidinone (DMI) in the spectrum of Raman scattering is manifested in the ν(CO) stretching vibration band at 1688 cm–1. A shift toward higher frequencies and a change in the ν(CO) DMI band profile in the DMI–CCl4 mixture with decreasing DMI mole fraction is explained by the redistribution of the intensities of components forming the complex band profile and the displacement of the equilibrium between the contents of the monomers and cyclic and chain dimers in the DMI molecules. Optimal geometries of the ground states of the DMI molecule and of the cyclic and chain DMI dimers and their vibrational spectra are calculated in the B3LYP/6-31++G(d, p) approximation. Keywords: Raman spectroscopy, 1,3-dimethyl-2-imidazolidinone, cyclic and chain DMI-DMI dimers.

The supramolecular structure of liquids is determined by non-covalent intermolecular interactions of hydrogen bond type, called van-der-Waals interactions, including dipole-dipole, induction, and dispersive components and by different degrees of molecule bonding. Exactly the intermolecular interactions often determine the structure and physical properties of liquid systems. 1,3-dimethyl-2-imidazolidinone (DMI) is an aprotic solvent with high dielectric permittivity (ε = 37.6) and large dipole moment (µ = 4.09 D) of the DMI molecule [1] localized mainly on the CO group. These properties and excellent solvation power for organic and inorganic compounds predetermine the complex supramolecular DMI structure. Aqueous and non-aqueous DMI solutions were studied in [2–5] by the method of IR absorption spectroscopy. According to the data of IR absorption spectroscopy, the frequency ν(CO) of DMI stretching vibrations is sensitive to the intermolecular environment [4]. The formation of intermolecular hydrogen bonds between the proton of the Cl3СН molecule and the oxygen atom of the carbonyl group of the DMI molecule as well as the interaction of the chlorine atom of the CCl4 molecule with the carbonyl group of the DMI molecule lead to a shift of ν(CO) of DMI toward lower frequencies when DMI is dissolved in CCl4/n-C6H14, CHCl3/n-C6H14, or CHCl3/CCl4 [3]. Based on the method of small-angle neutron scattering and measurements of the density of aqueous DMI solutions, Szekely et al. [5] concluded that the DMI molecules are prone to self-association. Investigations in an inert solvent medium allow sets of the most typical molecular associates to be detected and their contents to be calculated quantitatively by the methods of vibrational spectroscopy as well as preliminary conclusions to be made about types of their structures based on their spectral and structural correlations. The modern technique of determining the structure of molecular particles from their vibrational spectra is based on a comparison of the IR or Raman light scattering (RS) spectra calculated by the methods of quantum chemistry for possible variants of the structure of the examined compounds with their experimental spectra. The correct structure of molecular associates can be obtained using an integrated approach including combined spectral and quantum-chemical investigations.

Ufa State Aviation Technical University, Ufa, Russia, e-mail: [email protected]. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 69–73, October, 2014. Original article submitted February 25, 2014; revision submitted July 3, 2014. 1374

1064-8887/15/5710-1374 2015 Springer Science+Business Media New York

F Fig. 1. Regionn of the ν(CO) DMI vibratioon in the RS sppectrum of DM MI–CCl4 mixtuure for tthe DMI mole fraction x = 1..00 (curve 1), 00.3 (curve 2), 00.1 (curve 3), aand 0.04 (curvee 4).

In thee present work,, results of invvestigations of self-associatioon of DMI mollecules by the methods of Fo ourierttransform Ram man scattering (FTRS) specttroscopy and qquantum-chem mical modelingg are presentedd. The choice of the m method of FT TRS spectroscoopy was causeed by the factt that the ν(CO O) RS bands of stretching vvibrations are much nnarrower (appproximately by y a factor of 33–4) than the correspondingg absorption bbands. In addiition, RS bandds and considerable nnonlinear backkground are ssuperimposed on the ν(CO O) absorption band at low frequencies, which complicates ann analysis of the t band profiile. To elucidaate the existencce of the self--associates of DMI moleculees, the vvibrational speectra were meaasured for DMII strongly dilutted in a nonpollar CCl4 solvennt together witth quantum-cheemical calculation of optimal geomeetries of the sellf-associates annd their vibratiional spectra.

E EXPERIMEN NTAL The R RS spectra weere recorded w with an FT–Raman NXR 9650 spectromeeter in the reggion 70–3800 cm–1. A Nd:YVO4 laaser with waveelength of 10664 nm and outpput power up to 1.5 W was used as an exxcitation source. The error in determ mining the po osition of RS bbands in the sspectrum was 0.4 cm–1. DM MI (≥99.5%, A Acros Organicss) was discharged through freshly annealed a moleccular sieves andd then used wiithout further cclearing. The D DMI mole fracttion in tthe DMI–CCl4 mixture was varied from 1.00 to 0.04. The Fourier speectra were proccessed using thhe software paackage ppresented in [66], that alloweed computer prrocessing of coomplex spectraa (decompositiion into indiviidual bands, deetailed analysis, filtraation, and smooothing) to be pperformed. Thee profiles of thhe componentss were approxim mated by sym mmetric Voigt functionss. curves of the V D DISCUSSION N OF EXPERIIMENTAL R RESULTS The exxperimental RS S spectrum of DMI in the reggion of the ν(C CO) stretching vibration is shown in Fig. 1 for f the iindicated DMII concentrationns. With decreeasing DMI cooncentration inn the DMI–CC Cl4 mixture froom 1.00 to 0.0 04, the D DMI spectrum m changed in thhe region of thhe ν(CO) stretcching vibrationn (in this spectrral region, no C CCl4 RS bandss were observed). The m maximum of thhe ν(CO) band at 1688 cm–1 (Fig. 1) in thee RS spectrum is smoothly shhifted toward higher frequencies byy 19 cm–1 withh decreasing D DMI mole fracttion in the DM MI–CCl4 mixtuure. The band profile changees: the asymmetric R RS profile beccomes more ssymmetric, whhich is explainned by redistrribution of thhe intensities of the components of the complexx ν(CO) band profile and deemonstrates thhe displacemennt of the equillibrium between the contents of diffferent DMI seelf-associates w with the monoomer DMI mollecules. This ssuggests that w with decreasing g DMI

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F Fig. 2. Regionn of the ν(CН) DMI vibrationn in the RS speectrum of the D DMI–CCl4 mixxture for tthe DMI mole fraction x = 1..00 (curve 1), 00.3 (curve 2), 00.1 (curve 3), aand 0.04 (curvee 4).

DMI moolecule

Cyclic dimer Figg. 3. DMI moleecule and cycliic dimer.

concentration in the DMI–CC Cl4 mixture, seelf-associates aare dissociated and the fractioon of the monoomer DMI mollecules tthat have highher ν(CO) freqquency is incrreased. For thiis reason, the maximum of the ν(СO) baand in the spectra is displaced towaard higher freqquencies, and tthe asymmetryy of the band pprofile gradually vanishes. W With decreasingg DMI m mole fraction in the DMI–C CCl4 mixture, qqualitative chaanges were noot observed in other frequenccy ranges of the t RS o CH stretchinng vibrations oof DMI is show wn in Fig. 2. W With decreasingg DMI mole fraaction, spectra of lighht. The region of tthe light intenssity of the bandd profile in thee RS spectrum decreases; how wever, no assoociations of thee DMI moleculles are observed in thee region of CH H vibrations.

R RESULTS OF F QUANTUM M-CHEMICAL L CALCULA ATIONS To eluucidate the poossibility of exxistence of DM MI self-associaates and to obbtain their optiimal geometriees, we pperformed quaantum-chemicaal calculations. The geometrries of the grouund states of tthe DMI moleecules and asso ociates w were optimizeed by the DFT T method in the B3LYP/6--31++G(d, p) approximationn [7]. The fuundamental vib bration frequencies annd the energy of o associate formation were calculated takiing into accounnt the basis seet superposition n error (BSSE). The sstable structurees are chain (oof type I and ttype II) and cyyclic dimers shhown in Figs. 3 and 4. The stable dimers are mainly formed duue to the interaaction of moleccular dipoles. T This is caused by the large ddipole moment of the D DMI moleculee.

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Vibration Frequuencies ν(CO)) of the Monom mers and Assoociated DMI M Molecules and Energy Solvattion TABLE1. V Characteristtics (in kJ/molee) Calculated in the IEFPCM M/B3LYP/6-31+ ++G (d, p) Appproximation Complex DM MI molecule (gaas) DMII molecule (CC Cl4) Chaain dimer I (gaas) Chaain dimer I (CC Cl4) Chaain dimer II (gaas) Chaiin dimer II (CC Cl4) Cyyclic dimer (gass) Cycclic dimer (CCl4)

ν (CO), cm–1 1777 1752 1771 (as) 1763 (s) 1750 (as) 1745 (s) 1770 (as) 1760 (s) 1748 (as) 1742 (s) 1771 (as) 1766 (s) 1749 (аs) 1747 (s)

–Es

–Edisp

Еreep

Ecav

Еnonel

–E Eel

12.76

39.79

1.555

61.25

23.05

35.81

19.75

67.28

2.334

117.95

53.01

72.76

19.25

65.31

2.330

113.72

50.71

69.96

17.95

69.07

2.447

114.27

47.66

65.61

Chaiin dimer I

Chaain dimer II Fig. 4. DM MI chain dimerrs.

v DM MI spectrum deemonstrates thhat the ν(СO) DMI frequenccy is sensitive to the Calcuulation of the vibrational m molecular envvironment and is i displaced tooward lower freequencies wheen the dimers aare formed. Thhe ν(СO) frequ uencies of the DMI moolecule in the structure of asssociates are prresented in Tabble 1. Taking into account thhe BSSE, the energy e of the dimer foormation was 10–11 kJ/mol both for chainn and cyclic dim mers. This testtifies to the equuiprobable exiistence of both cyclic and chain dimers in the DMII–CCl4 mixturee. To esttimate the inflluence of the ddistant environnment of the D DMI moleculess, the nonspeciific solvation among a tthe molecules,, DMI dimers,, and CCl4 moolecules was taaken into accoount using one of the variantts of the Polarrizable Continuum M Model (PCM) for f the integraal equation foormalism variaant (IEFPCM model) [7]. T Table 1 presen nts the frequencies ν((CO) of symm metric (s) and antisymmetricc (as) stretchinng vibrations oof monomers aand associated d DMI m molecules in tthe gas phase calculated in the IEFPCM/B B3LYP/6-31++G(d, p) apprroximation. Thhe ν(CO) vibraational frequencies off the DMI moolecules in thee structure of self-associatess and monomeer DMI moleccule decrease in the pprocess of trannsition from thee gas phase to the CCl4 envirronment. Table 1 also gives thhe free solvatioon energy Es beeing the sum of the followingg contributionss:

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F Fig. 5. Resullt of decompoosition of thee ν(CO) DMI band in thee RS spectrum m into ccomponents. Here H curve 1 iis for the monnomers, curve 2 is for the aantisymmetric dimer vvibrations, andd curve 3 is forr the symmetricc dimer vibratiions.

Es = Eel + Ecav + Edisp + Errep, w where Eel is thhe energy of ellectrostatic inteeraction betweeen the DMI chharges and CC Cl4 molecules, Ecav is the cavitation energy requireed for cavity formation f in tthe dielectric ((solvent), Edispp is the disperssive componennt of the interraction energy, and Errep is the repullsion energy. T The energy of nonelectrostattic interaction Enonel involvess Ecav, Edisp, an nd Erep. The contributiions of nonelecctrostatic and eelectrostatic coomponents to Es are comparaable with prevaalence of Eel. The T Es vvalues for dim mers of differennt types are cloose and are m much greater than those for m monomers. Thee contributionss of all hhydrogen atom ms to Es are equual to –4.39 kJJ/mole (monom mers), –10.42 J//mole (cyclic ddimers), –7.24 kJ/mole (type I) and ––6.77 kJ/mole (type II). For chain dimers (type I or II), thhe contributionns from the O1 atom equal to –7.36 kJ/molee (type II) and –7.49 kkJ/mole (type II) I prevail, andd the total conttributions from m the carbon attoms С23, С27, С30, and С34 are equal to –4.35 kJ/mole (type I) and –3.55 kkJ/mole (type II). R REGION OF (CO) STRE ETCHING VIB BRATIONS IN N THE RS SP PECTRUM Accorrding to the reesults of quanntum-chemical calculations, the frequencyy of symmetricc DMI vibratioons in dimers is ν(СO O) = (1763 ± 3) cm–1, the fr frequency of anntisymmetric vvibrations is νν(СO) = (17700 ± 1) cm–1, annd the frequency of tthe isolated DM MI molecule iss ν(СO) = 17777 cm–1. Since the results off quantum-chem mical modeling give iidentical symm metric and antiisymmetric vibbration frequenncies for differrent dimers, deecomposing thhe experimentaal band pprofile into inddividual compoonents, we do not distinguishh the vibrationnal frequenciess of separate diimers (Fig. 5). In the pprocess of deccomposition off the band proffile with error of ±1 cm–1, w we distinguish tthe componentts whose frequ uencies are referred too the symmettric and antisyymmetric ν(СO O) DMI vibraations in the ddimer structuree and to the ν(СO) vvibrations of thhe monomer DMI D molecule. Here band 2 is the result of superposition of antisymmettric dimer vibraations, and band 3 is tthe result of suuperposition off the symmetricc dimer vibratioons. Resultts of decompoosition of the experimental νν(СO) band pprofile in the R RS spectrum iinto componennts are ppresented in T Table 2. The ν(СO) ν vibratioonal frequencyy for the DMI molecule is (1709 ± 2) cm m–1, the frequenncy of –1 – antisymmetric dimer vibratioons is (1697 ± 2) cm , and tthe frequency of symmetric vibrations is (1688 ± 1) cm–1 . The observed diffeerence betweenn the frequenciies of the symm metric and anttisymmetric vibbrations of thee С=О bond is about 8 cm–1, which is comparablee with the resullts of quantum m-chemical calcculations (7 cm m–1). With decrreasing mole frraction of DMI, the ν((СO) vibrationnal frequency oof the DMI moonomer molecuule is smoothlyy shifted towarrd lower frequuencies bby 4 cm–1 due to the influencce of the solvatte CCl4 environnment on this vvibration.

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TABLE 2. Components of the v(СO) Vibration Band Profile of the DMI Molecule in the RS Spectrum of the DMI–CCl4 mixture DMI mole I, rel. I, rel. vs, cm–1 vas, cm–1 Vmon, cm–1 I, rel. units fraction units units 1 1688 145 1696 94 1710 68 0.8 1689 135 1696 116 1710 52 0.6 1689 137 1698 72 1709 67 0.5 1689 148 1698 63 1709 51 0.1 1689 3 1695 46 1707 46 0.08 1689 0 1696 28 1707 36 0.06 1689 0 1698 12 1707 39 0.04 1689 0 1699 3 1706 46 Note. Here C indicates the relative content of DMI dimers and monomers.

C, dimers C, monomers 78 83 76 81 52 44 24 05

22 17 24 19 48 56 76 95

The relative contents of the DMI dimers and monomers were also calculated. Quantitative calculations of their relative contents C were performed under assumption of identical scattering cross sections in the RS spectrum of light by molecules forming different associates and molecules in the monomer state from the relative contribution of the integral intensities of СO stretching vibrations of differently associated molecules IA to the total intensity IΣ: C = (IA/IΣ)100%. With decreasing DMI mole fraction, the relative contribution of dimers decreases, and that of monomers increases.

CONCLUSIONS 1. The supramolecular DMI structure is formed by the monomers and chain and cyclic dimers. The ν(CO) DMI band in the RS spectra is the result of superposition of С=О band vibrations of monomers and cyclic and chain dimers comprised in the DMI molecules. The comparative analysis of the RS spectra in the region of ν(CO) has allowed us to calculate the relative contents of the DMI monomers and cyclic and chain dimers. 2. In the B3LYP/6-31++G(d, p) approximation, the geometries of the DMI self-associates were determined, and the energies of formation and vibrational spectra of complexes in the gas phase and in the CCl4 environment (IEFPCM model) were calculated. This work was supported in part by the Ministry of Education and Science of the Russian Federation under the basic part of the State Assignment to Educational Institutions of Higher Education.

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B. J. Barker, J. Rosenfarb, and J. A. Caruso, Angew. Chem., 91, 560–564 (1979). E. Vrolix, M. Goethals, and Th. Zeegers-Huyskens, Spectrosc. Lett., 26, No. 3, 497–507 (1993). R. A. Nyquist, C. L. Putzig, and T. D. Clark, Vibration. Spectrosc., 12, No. 1, 81–91 (1996). E. I. Harnagea and P. W. Jagodzinski, Vibration. Spectrosc., 10, No. 2, 169–175 (1996). N. K. Szekely, L. Almasy, and G. Jancso, J. Mol. Liquids, 136, No. 3, 184–189 (2007). OMNIC 7.4.127. Thermo Electron Corporation; http://www.thermo.com/spectroscopy. M. J. Frisch, G. W. Trucks, H. B. Schlegel, et al., Gaussian 03, Revision B.03, Gaussian, Inc., Pittsburgh PA (2003).

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