Vibrational and UV spectra, first order hyperpolarizability, NBO and HOMO–LUMO analysis of 4-chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoyl-benzamide

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14

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Vibrational and UV spectra, first order hyperpolarizability, NBO and HOMO–LUMO analysis of 4-chloro-N-(2-methyl-2,3dihydroindol-1-yl)-3-sulfamoyl-benzamide S. Muthu a,⇑, T. Rajamani b, M. Karabacak c, A.M. Asiri d,e a

Department of Applied Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602105, Tamilnadu, India Department of Physics, Global Institute of Engineering And Technology, Melvisharam, Vellore, India Department of Mechatronics Engineering, H.F.T. Technology Faculty, Celal Bayar University, Turgutlu, Manisa, Turkey d Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia e Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia b c

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Spectroscopic properties were

examined by FT-IR and FT-Raman techniques.  The vibrations were assigned with PED.  NLO and NBO analysis of the title molecule were studied.  HOMO and LUMO energies and MEP distribution of the molecule were calculated.  Thermodynamic properties were investigated.

a r t i c l e

i n f o

Article history: Received 3 September 2013 Received in revised form 19 October 2013 Accepted 31 October 2013 Available online 8 November 2013 Keywords: DFT Vibrational analysis First order hyperpolarizability NBO and NLO analysis MEP

a b s t r a c t In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4000–100 cm1 and 4000–400 cm1, respectively, for 4-chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoyl-benzamide (C16H16O3N3SCl) molecule. Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) and 6-311G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (b0) and related properties (l, a, and Da) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The UV–vis spectrum of the compound was recorded in the region 200–400 nm in ethanol and electronic properties such as excitation energies, oscillator strength and wavelength were calculated by TD-DFT/ B3LYP method. Molecular electrostatic potential (MEP) and HOMO–LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures. Ó 2013 Elsevier B.V. All rights reserved.

Introduction 4-Chloro-N-(2-methyl-2,3-dihydroindol-1-yl)-3-sulfamoyl-benzamide (CMDS) is an oral anti-hypersensitive diuretic agent indi⇑ Corresponding author. Tel.: +91 9443690138; fax: +91 4427162462. E-mail addresses: [email protected], [email protected] (S. Muthu). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.115

cated for the treatment of hypertensive and edema [1]. Its molecule contains both a polar sulfamoyl chlorobenzamide moiety and a lipid-soluble methylindoline moiety. It differs chemically from the thiazides in that it does not possess the thiazide ring system and contains only one sulfonamide group. It is a white to yellow-white crystalline. It is used to treat high blood pressure. Lowering high blood pressure helps prevent strokes, heart attacks

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and kidney problems. It acts by preventing the kidney from reabsorbing salt and water that are intended for being eliminated in the urine. It is used to get rid of extra fluid in the body. Therefore it is important to analyze the characterization of the title compound for future studies. Moreover, researchers are interested in theoretical studies to support the experimental evidences since computational methods are reliable to characterize the molecule because of their efficiency and accuracy with regard to the evaluation of a number of molecular properties [2]. Rus et al. [3] studied the compatibility of the title compound. Dissolution method validation of CMDS has been studied by Kumar et al. [4]. Literature survey reveals that so far there is no complete experimental and theoretical study for the title compound. This inadequacy observed in the literature encouraged us to make this theoretical and experimental vibrational spectroscopic research based on the molecule to give a correct assignment of the fundamental bands in experimental FT-IR and FT-Raman spectra on the basis of calculated PED. The electronic transitions were analyzed via UV–vis spectroscopic techniques. Therefore, the present study aims to give a complete description of the molecular geometry, molecular vibrations, electronic features and thermodynamics properties of the present molecule. Experimental details The compound CMDS is purchased from M/S Aldrich chemicals, (USA) with spectroscopic grade and it is used as such without any further purification. The FT-IR spectrum of the compound was recorded in Perkin–Elmer 180 Spectrometer between 4000– 100 cm1. The spectral resolution is ±2 cm1. The FT-Raman spectrum of CMDS was also recorded in the same instrument with FRA 106 Raman module equipped with Nd:YAG laser source operating in the region 100–4000 cm1 at 1.064 lm line widths with 200 mW powers. The spectra were recorded with scanning speed of 30 cm1 min1 of spectral width 2 cm1. The frequencies of all sharp bands are accurate to ±1 cm1. The UV spectrum of CMDS was measured in the region 200–400 nm in ethanol using SHIMADZU UV-1601PC, UV–vis recording spectrometer. Computational details For meeting the requirements of both accuracy and computing economy, theoretical methods and basis sets should be considered. DFT has proved to be extremely useful in treating electronic structure of the molecules. The molecular structure optimization of the title compound and corresponding vibrational harmonic frequencies were calculated using DFT with Becke-3-Lee–Yang–Parr (B3LYP) combined with standard 6-31G(d,p) and 6-311G(d,p) basis sets using Gaussian 03W program package without any constraint on the geometry [5]. The optimized geometrical parameters, energy, fundamental vibrational frequencies, first order hyperpolarizability and related properties (l, a, and Da) were calculated theoretically using Gaussian 03W package. GaussView 5.0.8 program has been used to construct optimized molecular geometry, HOMO, LUMO energy distributions and HOMO–LUMO energy gap [6,7]. The Cartesian representation of the theoretical force constants have been computed at optimized geometry by assuming C1 point group symmetry. A comparison is made between the theoretically calculated frequencies and the experimentally measured frequencies. To improve the agreement between the predicted and observed frequencies, the computed harmonic frequencies are usually scaled for comparison. For this purpose the scaling of force field was performed according to SQMFF procedure [8], the Cartesian representation of the force constants were transferred

to a non redundant set of local symmetry coordinates, chosen in accordance to the recommendations of Pulay et al. [9]. The descriptions of the predicted frequencies during the scaling process were followed by the PED matrix. The characterization of the normal modes using PED was done with the MOLVIB program (Version V7.0-G77) written by Sundius [10,11]. The symmetry of the molecule was also helpful in making vibrational assignments. The symmetries of the vibrational modes were determined by using the standard procedure [12] of decomposing the traces of the symmetry operation into the irreducible representations. The symmetry analysis for the vibrational modes of CMDS is presented in detail in order to describe the basis for the assignments. By combining the result of the GaussView program [6] with symmetry considerations, vibrational frequency assignments were made with a high degree of confidence. There is always some ambiguity in designing internal coordinates. However, the defined coordinates form complete set and matches quite well with the motions observed using Gauss View program. Prediction of Raman intensities The Raman activities (SRa) calculated with the Gaussian 03 program were converted to relative Raman intensities (IRa) using the following relationship derived from the intensity theory of Raman scattering [13,14].

Ii ¼

f ðm0  mi Þ4 Si mi ½1  expðhcmi =kTÞ

ð1Þ

where m0 is the laser exciting wavenumber in cm1 (in this work, we have used the excitation wavenumber m0 = 9398.5 cm1, which corresponds to the wavelength of 1064 nm of a Nd:YAG laser), mi the vibrational wavenumber of the ith normal mode (in cm1) and Si is the Raman scattering activity of the normal mode mi, f(is a constant equal to 1012) is a suitably chosen common normalization factor for all peak intensities. h, k, c and T are Planck constant, Boltzmann constant, speed of light and temperature in Kelvin, respectively. Non-linear optical effects Non-linear optical (NLO) effects arise from the interactions of electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristics from the incident fields [15,16]. NLO is at the forefront of current research because of its importance in providing the key functions of frequency shifting, optical modulation, optical switching, optical logic, and optical memory for the emerging technologies in areas such as telecommunications, signal processing, and optical interconnections [17–20]. Organic molecules that exhibit extended p conjugation, in particular, show enhanced second order NLO properties [21]. The first hyperpolarizability (b0) of this novel molecular system and the related properties (b0, a0) of CMDS are calculated using the B3LYP/6-31G(d,p) basis set, based on the finite field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. The first hyperpolarizability is a third-rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Klein man symmetry [22,23]. It can be given in the lower tetrahedral. The components of b are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogenous, this expansion becomes:

E ¼ E0  la F a  1=2aab F a F b  1=6babc F a F b F c þ   

ð2Þ

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where E0 is the energy of the unperturbed molecules, Fa, the field at the origin and la, aab and babc are the components of dipole moment, polarizability and the first hyperpolarizabilities, respectively. The total static dipole moment (l), polarizability (a), mean polarizability (Da) and the mean first hyperpolarizability (b0), using the x, y, z components are defined as follows:



l ¼ l2x þ l2y þ l2z a¼

12

ð3Þ

 1 axx þ ayy þ azz 3

ð4Þ

i12 1 h Da ¼ pffiffiffi ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xz þ 6a2xy þ 6a2yz 2 ð5Þ

h i12 b0 ¼ ðbxxx þ bxyy þ bxzz Þ2 þ ðbyyy þ byzz þ byxx Þ2 þ ðbzzz þ bzxx þ bzyy Þ2 ð6Þ Since the values of the a and b0 of the Gaussian 03 output are reported in atomic units (a.u.), the calculated values have been converted into electrostatic units (esu) (for a: 1 a.u. = 0.1482  1024 esu; for b: 1 a.u. = 8.639  1033 esu). The total molecular dipole moment and first order hyperpolarizability are 4.6859 debye and 1.672  1030 esu, respectively and are depicted in Table 1. First order hyperpolarizability of the title molecule is ca. 5 times greater than those of urea (l and b of urea are 1.3732 debye and 0.3728  1030 esu) obtained by B3LYP/6-31G(d,p) method. The large value of hyperpolarizability, b0 which is a measure of non linear optical activity of the molecular system, is associated with the intra molecular charge transfer, resulting from the electron cloud movement through p conjugated frame work from electron donor to electron acceptor groups. The physical properties of these conjugated molecules are governed by the high degree of electronic charge delocalization along the charge transfer axis and by the low band gaps. Therefore, we conclude that the title molecule is an attractive object for future studies of non-linear optical properties. Results and discussions Molecular geometry The molecular structure along with numbering of atoms of CMDS is obtained from Gaussian 03 and GAUSSVIEW programs and is shown in Fig. 1. The most optimized structural parameters (bond length and bond angle) calculated by DFT/B3LYP with 6-31G(d,p) and 6-311G(d,p) basis sets are compared with experimental data [24] are presented in Table 2. From the theoretical values, it is found that some of the calculated parameters are slightly

deviated from the experimental values, due to fact that the theoretical calculations belong to molecule in the gaseous phase and the experimental results belong to molecule in solid state. By allowing the relaxation of all parameters, the calculations converge to optimized geometries, which correspond to true energy minima, as revealed by the lack of imaginary frequencies in the vibrational mode calculation. This molecule has sixteen CAC bond lengths, thirteen CAH bond lengths, three NAH bond lengths, three CAN bond lengths, two SAO bond lengths and one NAN, CAO, CACl, CAS, SAN bond lengths. The calculated bond length values for CAC and CAH in the benzene ring vary from 1.384–1.401 Å and 1.081–1.085 Å by B3LYP/6-311G(d,p) basis set, respectively and well agreed with the experimental values [24]. The calculated bond length for C@O is found to be 1.212 Å which is complied with experimental value [24]. The bond length value is found to be high for CAS bond. With the electron donating and withdrawing substituent on the benzene ring, the symmetry of the ring is distorted, yielding variation in bond angles at the point of substitution. In this study, the SAO and SAN bond lengths are predicted well with experiment values (see Table 2). The CACl bond length indicates a considerable increase when substituted in place of CAH, in other word, the bond length increases from CACl. This has been observed even in benzene derivatives [25–27]. The angles at the point of substitution C3AC4AC5 and C3AC2AC7 are 119.5° and 119.1°, respectively. The small difference between experimental and theoretical bond lengths and bond angles may be due to the presence of intermolecular hydrogen bonding or the experimental results belong to solid phase and theoretical calculations belong to gaseous phase. Vibrational assignments The maximum number of potentially active observable fundamentals of a non-linear molecule, which contains N atoms, is equal to (3N-6) apart from three translational and three rotational degrees of freedom [28,29]. The present molecule CMDS with 40 atoms and 114 normal modes of vibrations has C1 point group symmetry. The observed and simulated FT-IR and FT-Raman spectra of CMDS are shown in Figs. 2 and 3, respectively. Detailed description of vibrational modes can be given by means of normal coordinate analysis (NCA). For this purpose the full set of 148 standard internal valence coordinates were defined and were presented in Table 3. From these a non-redundant set of local symmetry coordinates were constructed much like the internal coordinates recommended by Fogarasi and Pulay [8] and were presented in Table 4. The observed and scaled theoretical frequencies using DFT/B3LYP with 6-31G(d,p) and 6-311G(d,p) basis sets with PED are listed in Table 5. Calculations were made for a free molecule in vacuum, while experiments were performed for solid phase. Therefore, the vibrational analysis obtained for CMDS with the

Table 1 Electric dipole moment l (Debye), polarizability a, mean polaraizability Da, b components and first order hyperpolarizability b0 value of CMDS calculated at B3LYP/6-31G(d,p). Parameters

a.u.

lx ly lz l axx axy ayy axz ayz azz a Da

3.6518 2.7479 1.0348 4.6859 216.0379 51.2869 272.3643 10.6178 12.4470 191.3883 226.5969 381.0326

esu (1024)

32.0168 7.6007 40.3644 1.5736 1.8446 28.3638 33.5817 56.4690

Parameters

a.u.

esu (1033)

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz b0

208.3734 90.5905 145.7344 37.6534 3.5403 3.5651 220.1503 39.1557 15.7676 56.2001 193.5848

1800.2000 782.6384 1259.0433 325.2992 30.5853 30.8003 1901.9448 338.2779 136.2208 485.5299 1672.4371

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S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14 Table 2 Optimized parameters (bond lengths (Å) and bond angles (°)) of CMDS. Parameters Bond lengths (Å) C1AC2 C1AO8 C1AN9 C2AC3 C2AC7 C3AC4 C4AC5 C4AS11 C5AC6 C5ACl27 C6AC7 N9AH10 N9AN17 S11AN14 N17AC18 N17AC25 C18AC19 C18AC26 C18AH31 C19AC20 C20AC21 C20AC25 C21AC22 C22AC23 C23AC24 C24AC25 SAO sulfurdioxide NAH amine CAH methylene CAH methyl CAH ring

Fig. 1. Numbering system adopted in the molecular structure of CMDS.

unscaled B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p) force field are generally somewhat greater than the experimental values due to neglect of anharmonicity in real system. A better agreement between the computed and experimental frequencies can be obtained by using different scale factors for different regions of vibrations. For that purpose, we have utilized different scaling factors for all fundamental modes to obtain the scaled frequencies of the compound. In B3LYP, the CAH stretching modes attributed >2000 cm1 with basis sets 6-31G(d,p) and 6-311G(d,p) are scaled with 0.954 and 0.96, respectively while 0.98 has been used for all other modes [29]. After scaled with the scaling factor, the deviation from the experiments is less than 10 cm1 with a few exceptions. In order to compare the experimental frequencies, we have found the correlation graphics based on the average theoretical and experimental data. Both experimentally and theoretically frequencies are showing good correlation (Supp. Mat. Figs. S1 and S2). The relations between the calculated and experimental wavenumbers are usually linear. The correlation values between the experimental (IR and Raman) frequencies and calculated vibrational frequencies (6-311G(d,p) basis set) are found to be 0.9997 and 0.9999 (Supp. Mat. Figs. S1 and S2). NAH vibrations The vibrations belonging to NAH stretching always occur in the region 3450–3250 cm1 which is the characteristic region for ready identification of this structure [30,31]. In this region, the bands are not affected appreciably by the nature of the substituents. The NH2 asymmetric stretching appears, as medium band at 3524 in IR spectrum and the corresponding stretching mode is computed at 3450 cm1. The symmetric NH2 stretching mode is observed at 3380 cm1 as a weak Raman band which is calculated at 3349 cm1. These asymmetric and symmetric vibrations are identified as pure mode with 100% PED values. In this study, the FT-IR band observed at 3344 cm1 is assigned to N9AH10 stretching vibration. The theoretically calculated values by B3LYP/6311G(d,p) method at 3344 cm1 (mode No. 112) is assigned to NAH stretching vibration. The PED of this mode is 99%. The PED for this mode suggests that this is a pure mode. The frequencies of the amino group appear 1630–1610 cm1 for the scissoring deformation and 1090–1060 cm1 for rocking deformation [32]. In this study, the amino scissoring bands are assigned in FT-Raman at 1597 cm1 and 1457 cm1 (1456 cm1 in FT-IR) which calculated at 1594 cm1 and 1458 cm1 B3LYP/6-311G(d,p) method. The rocking vibration of NH2 is observed at 1165 cm1 which calculated at 1156 cm1. According to the PED results, the calculated band at 568 cm1 which observed at 566 in FT-IR was assigned to wagging mode of amino group. Likewise, the twisting vibration

Experimentala

Bond angles (°) C2AC1AO8 C2AC1AN9 O8AC1AN9 C1AC2AC3 C1AC2AC7 C3AC2AC7 C2AC3AC4 C3AC4AC5 C3AC4AS11 C5AC4AS11 C4AC5AC6 C4AC5ACl27 C6AC5ACl27 C5AC6AC7 C2AC7AC6 C1AN9AN17 H10AN9AN17 C4AS11AO12 C4AS11AO13 C4AS11AN14 O12AS11AO13 O12AS11AN14 O13AS11AN14 S11AN14AH15 S11AN14AH16 H15AN14AH16 N9AN17AC18 N9AN17AC25 C18AN17AC25 N17AC18AC19 N17AC18AC26 CACAH ring HACAH Methyl a

1.517 1.208 1.369 1.420 1.420 1.420 1.420 1.790 1.420 1.719 1.420 1.012 1.352 1.696 1.470 1.462 1.608 1.523 1.113 1.497 1.420 1.420 1.420 1.420 1.420 1.420 1.450 1.020 1.113 1.113 1.100 123.5 113.3 123.1 117.6 117.6 120.0 120.0 120.0 120.0 120.0 120.0 120.0 120.9 120.0 120.0 120.9 120.9 109.5 109.5 109.5 116.6 109.5 101.9 109.5 109.5 104.5 126.0 126.0 108.0 107.3 110.7 120.0

B3LYP/631G(d,p) 1.507 1.219 1.381 1.399 1.399 1.396 1.404 1.809 1.397 1.744 1.389 1.016 1.386 1.696 1.490 1.411 1.548 1.521 1.104 1.512 1.387 1.402 1.403 1.396 1.401 1.392 1.463 1.017 1.097 1.094 1.085 121.6 114.7 123.7 123.8 117.1 119.1 120.8 119.5 120.3 120.2 119.8 122.1 118.1 120.2 120.6 120.9 117.0 108.2 108.1 102.4 122.4 107.2 106.9 108.7 108.5 111.7 116.0 117.0 109.5 108.1 112.1 119.9 108.3

B3LYP/6311G(d,p) 1.508 1.212 1.380 1.396 1.396 1.394 1.401 1.814 1.393 1.744 1.387 1.015 1.383 1.691 1.490 1.409 1.547 1.521 1.103 1.511 1.384 1.400 1.401 1.393 1.398 1.390 1.456 1.015 1.095 1.093 1.083 121.5 114.7 123.8 123.9 117.1 119.0 120.8 119.6 120.2 120.2 119.7 122.2 118.1 119.3 120.6 121.3 117.2 108.1 108.0 102.3 122.4 107.1 107.0 109.5 109.4 111.9 116.4 117.2 108.3 102.4 112.2 120.0 108.3

Taken from Ref. [24].

(378 cm1 in FT-Raman, mode 23) is also in good agreement with literature values [32,33]. The other NAH in-plane bending (scissoring and rocking) and out-of-plane bending (wagging and torsion) vibrations are shown in Table 5.

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14

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Fig. 3. Comparative representation of FT-Raman spectra for CMDS. Fig. 2. Comparative representation of FT-IR spectra for CMDS.

CAH vibrations The existence of one or more aromatic rings in a structure is normally readily determined from the CAH and C@C@C ring related vibrations. The substituted benzene like molecule gives rise to CAH stretching, CAH in-plane and CAH out-of-plane bending vibrations. The aromatic structure shows the presence of CAH stretching vibrations in the region 3100–3000 cm1 which is the characteristic region for the ready identification of CAH stretching vibrations [34,35]. In this region, the bands are not affected appreciably by the nature of the substituent. This mode is calculated in the range 3068–3016 cm1 with B3LYP/6-311G(d,p) (mode Nos. 111–105). The PED for this mode suggests that this is a pure mode. The CAH in-plane bending frequencies appear in the range 1000–1300 cm1 and are very useful for characterization purpose [34]. In this work, the in-plane bending vibrations were observed in the range 1249–1019 cm1 in FT-IR and at 1261–1019 cm1 in FT-Raman. The theoretically scaled vibrations by B3LYP/6311G(d,p) level also shows good agreement with experimentally recorded data. The CAH out-of-plane bending vibrations are strongly coupled vibrations and occur in the region 1000– 750 cm1 [36]. In this work, the out-of-plane bending vibrations were recorded in the range 988–876 cm1 in FT-IR and at 1003– 852 cm1 in FT-Raman. Both the in-plane and out-of-plane bending vibrations are described as mixed modes. CH3 vibrations The title molecule under consideration possesses only one CH3 group. For the assignments of CH3 group frequencies one can

expect nine fundamentals can be associated to each CH3 group, namely the symmetrical stretching and asymmetrical stretching, in-plane stretching modes, symmetrical and asymmetrical deformation modes, in-plane and out-of plane rocking and twisting modes. Methyl groups are generally referred as electron donating substitution in the aromatic ring system. The CAH stretching vibrations of the methyl group lie in the region 2975–2840 cm1 [35,37]. The first of these results from the antisymmetric stretching of CH3 mode in which the two CAH bonds of the methyl group are expanding while the third one is contracting. The second arises from the symmetric stretching in which all the three CAH bonds expand and contract in phase. The asymmetric stretching for the CH3 has magnitude higher than the symmetric stretching [23,35,37]. The asymmetric stretching of CH3 observed in FT-Raman at 2977 cm1 was calculated at 2971 cm1. The PED of this mode is 96%. The CH3 symmetric stretching mode is predicted by B3LYP/6-311G(d,p) method at 2896 cm1 which observed at 2919 and 2916 cm1 in FT-IR and FT-Raman, respectively. The deformation of CH3 group is usually observed in the range 1450– 1400 cm1 for methyl substituted aromatic rings [37,38]. According to the above references, in this title molecule the peaks at 1456 cm1 in FT-IR and 1457 cm1 in FT-Raman are assigned to CH3 in-plane bending deformation vibrations while the peak at 1120 cm1 FT-Raman are assigned to CH3 in-plane rocking modes. The methyl group assignments proposed in this study is also in agreement with the literature values [16,30,35].

CH2 vibrations The stretching modes of the CH2 groups were recorded in the region 2950–2860 cm1 [37]. The major coincidence of theoretical

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Table 3 Definition of internal coordinates of CMDS. No.

Symbol

Type

Definitiona

Stretching 1–8 9–24

ri Ri

CAH CAC

25–27

Pi

28–29 30 31–33 34–35 36 37 38–39 40 41 42

Bi Qi Si Bi Si Si Bi Si Si Si

CAH (methyl) CH2 CO CN NH2 NN CS SO2 SN NH CCl

C3AH40, C6AH38, C7AH39, C18AH31, C21AH34, C22AH33, C22AH32, C24AH37 C1AC2, C2AC3, C3AC4, C4AC5, C5AC6, C6AC7, C7AC2, C18AC19, C18AC26, C19AC20, C20AC25, C20AC21, C21AC22, C22AC23, C23AC24, C24AC25 C26AH29, C26AH30, C26AH28

In plane bending 43–48 bi 49–53 bi 54–59 bi 60–73 bi 74–77 78 79 80 81 82–83 84–85 86 87 88 89 90 91–92 93–94 95–97 98–100 101 102–103 104–105 106 107 108–109 110

ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai ai

Out of plane bending 111–117 xi

a

Ring 1 Ring 2 Ring 3 CACAH CACAH(CH2) CACAO NACAO CANAH NANAH CANAN CACAC CACAC CACAH NACAH CACAC NACAC CCCl CCS CCH (CH3) HCH (CH3) OSO OSN CSO CSN HNH SNH CCN CAH

118 119 120 121 122 123 124 125 126

xi xi xi xi xi xi xi xi xi

CACl CAS CAO NAH CAC NN SC NS SN

Torsion 127–132 133–137 138–143

si si si

Ring 1 Ring 2 Ring 3

144–145 146 147 148

si si si si

CACH2 CACH3 SANH2 CASO2

C19AH35, C19AH36 C1AO8 C1AN9, C25AN17, C18AN17 N14AH15, N14AH16 N9AN17 C4AS11 S11AO12, S11AO13 S11AN4 N9AH10 C5ACl27 C2AC3AC4, C3AC4AC5, C4AC5AC6, C5AC6AC7, C6AC7AC2, C7AC2AC3 C18AC19AC20, C19AC20AC15, C20AC25AN17, C25AN17AC18, N17AC18AC19 C20AC21AC22, C21AC22AC23, C22AC23AC24, C23AC24AC25, C24AC25AC20, C25AC20AC21 C2AC7AH39, C6AC7AH39, C7AC6AH38, C5AC6AH38, C2AC3AH40, C4AC3AH40, C20AC21AH34, C22AC21AH34, C21AC22AH33, C23AC22AH33, C22AC23AH32, C24AC23AH32, C23AC24AH37, C25AC24AH37 C20AC19AH35, C20AC19AH36, C18AC19AH35, C18AC19AH36 C2AC1AO8 N9AC1AO8 C1AN9AH10 N17AN9AH10 C25AN17AN9, C18AN17AN9 C3AC2AC1, C7AC2AC1 C19AC18AC26 C19AC18AH31 N17AC18AC26 C19AC18AC26 N17AC18AC26 C4AC5ACl27, C6AC5ACl27 C5AC4AS11, C3AC4AS11 C18AC26AH29, C18AC26AH28, C18AC26AH30 H28AC26AH30, H28AC26AH29, H30AC26AH29 O12AS11AO13 O13AS11AN14, O12AS11AN14 C4AS11AO12, C4AS11AO13 C4AS11AN14 H15AN14AH16 S11AN4AH15, S11AN4AH16 C2AC1AN9 C5AC7AC6AH38, C6AC2AC7AH39, C2AC4AC3AH40, C20AC22AC21AH34, C21AC23AC22AH33, C22AC24AC22AH32, C23AC25AC24AH37 C4AC6AC5ACl27 C3AC5AC4AS11 C2AN9AC1AO8 C1AN17AN9AH10 N17AC19AC18AC26 C25AC18AN17AN9 O12AO13AS11AC4 H15AH16AN14AS11 O12AO13AS11AN14 C2AC3AC4AC5, C3AC4AC5AC6, C4AC5AC6AC7, C5AC6AC7AC2, C6AC7AC2AC3, C7AC2AC3AC4 C18AC19AC20AC25, C19AC20AC25AN17, C20AC25AN17AC18, C25AN17AC18AC19, N17AC18AC19AC20 C20AC21AC22AC23, C21AC22AC23AC24, C22AC23AC24AC25, C23AC24AC25AC20, C24AC25AC20AC21, C25AC20AC21AC22AC23 C20AC19AH35AH36, C18AC19AH35AH36 C18AC26A(H28AH29AH30) S11AN14AH15AH16 C4AS11AO12AO13

For numbering of atoms refer Fig. 1.

values with that of experimental values is found in the symmetric and asymmetric vibration of the methylene (ACH2A) moiety. For the assignments of CH2 group frequencies, basically six fundamentals can be associated to each CH2 group namely CH2 symmetric

stretch, CH2 asymmetric stretch, CH2 scissoring and CH2 rocking which belongs to in-plane vibrations and two out-of plane vibrations, viz., CH2 wagging and CH2 twisting modes, which are expected to be depolarized. The asymmetrical stretching and

7

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14 Table 4 Definition of local symmetry coordinates of CMDS. No.

Symbol

Definitiona

1–8 9–24 25

CH CC CH3ss

r1, r2, r3, r4, r5, r6, r7, r8 R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24 pffiffiffi ðP25 þ P26 þ P27Þ= 3 pffiffiffi ð2P25 þ P26 þ P27Þ= 6 pffiffiffi ðP26  P27Þ= 2 pffiffiffi ðB28 þ B29Þ= 2 pffiffiffi ðB28  B29Þ= 2 Q30 S31, S32, S33 pffiffiffi ðB34 þ B35Þ= 2 pffiffiffi ðB34  B35Þ= 2 S36 S37 pffiffiffi ðB38 þ B39Þ= 2 pffiffiffi ðB38  B39Þ= 2 S40 S41 S42 pffiffiffi ðb43  b44 þ b45  b46 þ b47  b48Þ= 6 pffiffiffiffiffiffi ðb43  b44 þ 2b45  b46  b47 þ 2b48Þ= 12 ðb43  b44 þ b45  b46Þ=2 B49 þ aðb50 þ b51Þ þ bðb52 þ b53Þ ða  bÞðb50  b51Þ þ ð1  aÞðb52  b53Þ pffiffiffi ðb54  b55 þ b56  b57 þ b58  b59Þ= 6 pffiffiffiffiffiffi ðb54  b55 þ 2b56  b57  b58 þ 2b59Þ= 12 (b54  b55 + b56  b57)/2 pffiffiffi pffiffiffi pffiffiffi pffiffiffi pffiffiffi pffiffiffi pffiffiffi ða60  a61Þ= 2; ða62  a63Þ= 2; ða64  a65Þ= 2; ða66  a67Þ= 2; ða68  a69Þ= 2; ða70  a71Þ= 2; ða72  a73Þ= 2 a74 + a75 + a76 + a77 a74  a75 + a76  a77 a74 + a75  a76  a77 a74  a75  a76 + a77 a78 a79 a80 a81 pffiffiffi ða82  a83Þ= 2 pffiffiffi ða84  a85Þ= 2 a86 a87 a88 a89 a90 pffiffiffi ða91  a92Þ= 2 pffiffiffi ða93  a94Þ= 2 pffiffiffi ða95  a96  a97 þ a98 þ a99 þ a100Þ= 6 pffiffiffi ða98  a99  2a100Þ= 6 pffiffiffi ða98  a99Þ= 2 pffiffiffi ð2a95  a96  a97Þ= 6 pffiffiffi ða96  a97Þ= 2 pffiffiffiffiffiffi ð4a101  a102  a103  a104  a105Þ= 20 (a102  a103 + a104  a105)/2 (a102  a103  a104 + a105)/2 pffiffiffiffiffiffi ð5a101  a106Þ= 26 pffiffiffiffiffiffi ða101  5a106Þ= 26 pffiffiffi ð2a107  a108  a109Þ= 6 pffiffiffi ða108  a109Þ= 2 pffiffiffi ða108 þ a109Þ= 2 a110 x111, x112, x113, x114, x115, x116, x117 x118 x119 x120 x121 x122 x123 x124 x125 x126 pffiffiffi ðs127  s128 þ s129  s130 þ s131  s132Þ= 6

26

CH3ips

27

CH3ops

28

CH2ss

29

CH2ass

30 31 32

CO CN NH2ss

33

NH2ass

34 35 36

NN CS SO2ss

37

SO2ass

38 39 40 41

SN NH CCl R1trigd

42

R1symd

43 44 45 46

R1asymd R2bend R2bend2 R3trigd

47

R3symd

48 49–55

R3asymd bCH

56 57 58 59 60 61 62 63 64

CH2scis CH2wag CH2rock CH2twist bCCO bNCO bCNH bNNH bCNN

65

bCCC

66 67 68 69 70 71

bCCC bCCH bNCH bCCC bNCC bCCCl

72

bCCS

73

CH3sb

74

CH3ipb

75

CH3opb

76

CH3ipr

77

CH3opr

78

SO2sd

79 80 81

SO2rock SO2twist SO2scis

82

CSNscis

83

NH2scis

84

NH2rock

85

NH2twist

86 87–93 94 95 96 97 98 99 100 101 102 103

xCH xCACl xCAS xCAO xNAH xCAC xNN xSC xNS xSN

bCCN

tRing1d

(continued on next page)

8

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14

Table 4 (continued)

a

No.

Symbol

Definitiona

104 105

tRing1symd tRing1assd

106 107 108

tR2torsion1 tR2torsion2 tRing3d

109 110

tRing3symd tRing3assd

111 112 113 114

CACH2 CACH3 SANH2 CASO2

(s127  s128 + s129  s130)/2 pffiffiffiffiffiffi ðs127 þ 2s128  s129  s130 þ 2s131  s132Þ= 12 b(s133 + s137) + a(s134 + s136) + s135 (a  b)(s137  s133)(1  a)(s136  s134) pffiffiffi ðs138  s139 þ s140  s141 þ s142  s143Þ= 6 (s138  s139 + s140  s141)/2 pffiffiffiffiffiffi ðs138 þ 2s139  s140  s141 þ 2s142  s143Þ= 12 s144, s145 s146 s147 s148

The internal coordinates used here are defined in Table 3.

symmetrical stretching [37] occur, respectively, near 2926 and 2853 cm1. In this study, the FT-Raman band at 2932 cm1 has been assigned to CH2 asymmetric stretching vibration, and the FT-IR band at 2900 and FT-Raman band at 2888 cm1 have been assigned to CH2 symmetric stretching vibrations. The theoretically computed values of CH2 asymmetric stretching give wavenumber at 2942 cm1 by B3LYP/6-311G(d,p) method (mode No. 102) and CH2 symmetric stretching exhibits wavenumber at 2876 cm1 (mode No. 100), which coincides exactly with experimental observation with the PED contribution of 71% and 65%, respectively. The scissoring vibration of CH2 at 1508 cm1 in FT-IR spectrum, the wagging vibration due to CH2 group at 1341 cm1 in FT-IR spectrum, the twisting vibration of CH2 at 1306 cm1 in FT-IR spectrum and at 1297 cm1 in FT-Raman band are presented in Table 5. These vibrations are well comparable with theoretically calculated value. Ring vibrations The ring stretching vibrations are very much important in the spectrum of aromatic compounds and are highly characteristic of the aromatic ring itself. However, empirical assignments of vibrational modes for peaks in the fingerprint region are difficult. Bands between 1400 and 1650 cm1 in benzene derivatives are assigned to these modes. In general, the bands are of variable intensity and observed at 1625–1590, 1590–1575, 1540–1470, 1460–1430 and 1380–1280 cm1 from the frequency ranges given by Varsanyi [35] for the five bands in the fingerprint region. In the present work, the bands width are of different intensity and observed at 1659, 1568, 1542, 1423, 1382 and 1359 cm1 in FT-IR have been assigned to C@C stretching vibrations. The theoretically calculated values at 1617, 1606, 1564, 1559, 1479, 1471, 1465, 1459, 1453, 1390, 1378, 1365, 1312 and 1290 cm1 by B3LYP/6-311G(d,p) method agrees well with the experimental values. SO2 vibrations The asymmetric stretching for the SO2, NH2, NO2, CH2 and CH3, etc. has magnitude higher than the symmetric stretching [39,40]. The symmetric and asymmetric SO2 stretching vibrations occur in the region 1125–1150 cm1 and 1295–1330 cm1 [41]. The intense signals appearing at 1418 and 1217 cm1 (IR) and 1414 and 1228 cm1 (Ra) were attributed to the SO2 antisymmetric and symmetric stretching fundamental modes for sulfamoyl fluoride substance by Alvareza et al. [42]. Dodoff [43] recorded the symmetric stretching mode at 1150 cm1 as strong peak, and the antisymmetric modes at 1341 and 1351 cm1 in infrared spectrum for N-3-Pyridinylmethanesulfonamide. In the present study, the symmetric S@O stretching vibration calculated at 1156 cm1 were obtained at 1165 cm1 in FT-IR spectrum. The band observed at 1336 cm1 in FT-Raman spectrum was assigned to antisymmetric S@O stretching vibrations which calculated at 1322 cm1. The other deformation of SO2 (scissoring, wagging rocking and torsion)

are shown in Table 5. A major coincidence of experimental values with that of literature [44,45] and theoretical results are found for above conclusions. CAN and CAS vibrations Because of the mixing of several bands, the identification of CAN vibrations is a very difficult task. Shanmugam and Sathyanarayana [46] assigned CAN stretching absorption in the region 1382–1266 cm1. In the present work, the band observed at 1306 cm1 in FT-IR and 1336 and 1297 cm1 in FT-Raman spectra have been assigned to CAN stretching vibration. According to PED results, he CAS and SAN stretching fundamental modes were calculated at 721 and 677 cm1 which observed at 720 and 677 cm1. The effect of sulfur atom can be seen for these vibration modes too. It should be noted that the scaled values are more reliable than unscaled ones. CACl vibrations The CACl stretching band is expected around 505–380 cm1 [37]. A weak FT-IR band at 470 cm1 and in FT-Raman at 477 cm1 is assigned to CACl stretching vibration. The unscaled wavenumber at 476 cm1 (mode 30) shows good correlation when compared with experimental counterpart. The CACl deformations are expected around 460–175 cm1 [37]. The theoretically computed wavenumber at 167 cm1 by B3LYP/6-311G(d,p) basis set is assigned to in-plane bending vibration. NBO analysis The NBO method of Weinhold et al. [47,48] provides a scheme appropriate to the analysis of Lewis acid/base interactions [47] as it emphasizes the calculation of delocalization of electron density into unoccupied orbitals. The NBO analysis is carried out by examining all possible interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’ (acceptor) non-Lewis NBOs, and estimating their energy by 2nd order perturbation theory. Since these interactions lead to loss of occupancy from the localized NBOs of the idealized Lewis structure into the empty non-Lewis orbitals, they are referred to as delocalization corrections to the zeroth-order natural Lewis structure. For each donor NBO (i) and acceptor NBO (j) with delocalization i ? j is estimated as 2

Eð2Þ ¼ DEij ¼ qi

Fði; jÞ ðej  ei Þ

ð7Þ

where qi is the donor orbital occupancy, ej and ei are diagonal elements orbital energies and F (i, j) is the off diagonal NBO Fock matrix element. NBO analysis has been performed on the molecule at the DFT/B3LYP/6-31G(d,p) level in order to elucidate the intra molecular, rehybridization and delocalization of electron density within the molecule, which are presented in Table 6. Percentage of s and

9

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14 Table 5 Observed and calculated vibrational frequencies of CMDS at B3LYP method with 6-31G(d,p) and 6-311G(d,p) basis sets. No.

Experimentala FT-IR

114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42

B3LYP/6-31G(d,p) FT-Raman

3524(m) 3380(w) 3344(w)

3040(m)

3010(vw) 2977(w)

2919(w) 2900(m) 2851(vw)

2932(w) 2916(w) 2888(s)

1659(s) 1597(w) 1568(m) 1542(vw) 1508(vw)

1456(m) 1423(m) 1382(m) 1359(m) 1341(m)

1457(m)

1381(m)

1336(m) 1306(m)

1297(w)

1261(m) 1249(m) 1201(vw)

1165(m) 1143(m) 1120(m) 1115(m)

1093(m) 1072(m)

1086(m)

1053(vw) 1035(vs) 1019(m) 988(m)

1019(w) 1003(w) 941(vw)

916(m) 899(m) 876(m)

765(m)

720(w)

875(w) 852(m)

B3LYP/6-311G(d,p)

Unscaled

Scaled

Unscaled

Scaled

3627 3514 3511 3235 3231 3218 3210 3202 3188 3179 3139 3124 3101 3053 3030 2960 1791 1665 1653 1639 1606 1591 1547 1521 1511 1506 1500 1496 1494 1430 1414 1405 1387 1363 1352 1336 1329 1312 1290 1280 1272 1231 1216 1187 1184 1170 1147 1142 1132 1124 1113 1094 1090 1077 1051 1049 997 975 965 942 940 931 916 895 871 867 865 832 808 769 762 748 734

3460 3353 3350 3086 3082 3070 3063 3055 3041 3033 2994 2980 2959 2912 2891 2824 1755 1631 1620 1607 1573 1559 1516 1490 1481 1476 1470 1466 1464 1402 1386 1377 1360 1336 1325 1309 1303 1286 1265 1254 1246 1206 1191 1163 1160 1147 1124 1119 1109 1102 1090 1073 1068 1056 1030 1028 977 956 946 923 921 912 898 878 854 850 848 815 792 754 747 733 720

3616 3510 3505 3216 3212 3199 3193 3185 3170 3162 3114 3101 3084 3035 3015 2943 1772 1650 1639 1626 1596 1591 1543 1509 1501 1495 1489 1488 1483 1419 1406 1393 1379 1349 1339 1324 1317 1302 1287 1274 1263 1226 1210 1182 1179 1166 1142 1135 1128 1115 1109 1090 1085 1073 1048 1044 1005 979 962 943 933 927 916 893 865 864 859 831 804 773 763 747 735

3450 3349 3344 3068 3064 3052 3046 3038 3024 3016 2971 2958 2942 2896 2876 2807 1737 1617 1606 1594 1564 1559 1512 1479 1471 1465 1459 1458 1453 1390 1378 1365 1351 1322 1312 1298 1290 1276 1261 1249 1237 1202 1186 1159 1156 1143 1119 1112 1105 1093 1087 1069 1063 1051 1027 1024 985 959 943 924 915 908 898 875 848 846 842 815 788 758 747 732 721

Assignments based on PED (6-311G(d,p); P10%)b

tasNH2(100) tsNH2(100) tNH(99) tCH(100) tCH(100) tCH(100) tCH(99) tCH(98) tCH(97) tCH(96) tasCH3(96) tasCH3(95) tasCH2(71) tsCH3(67) tsCH2(65) tCH(60) + tsCH2(34) tCO(57) tCC(66) tCC(69) dNH2(80)

tCC(65) tCC(32) dCH2(74)

tCC(50) dCC(69)

tCC(63) tCC(60) dNH2(80) + dCH3(15)

tCC(34) tCC(32) + wCH3(17) tCC(32) tCC(47) wCH2(78) + tCC(21) tasSO2(69) + tCN(30) tCC(32) tCH2(54) + tCN(45) tCC(20) wCH2(78) + tCC(21) bCAH(30) + tCS(16) tCN(58) + tCS(20) tCS(19) + bCAH(12) tCH2(69) bCAH(67) tCS(19) + bCAH(12) tsSO2(65) + rNH2(34) bCAH(61) + tNN(17) rCH3(69) bCH(66) bCH(67) bCH(54) bCH(63) bCH(56) bCH(52) + bCCC(38) bCH(61) + bCCC(37) bCH(52) + bCCC(38) bCH(66) xCH(51) xCH(61) xCH(83) xCH(86) xCH(81) xCH(85) xCH(80) xCH(82) xCH(84) xCH(82) xCH(83) xCH(72) xCH(91) bCCC(57) bCCC(68) bCCC(66) tCS(70) (continued on next page)

10

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14

Table 5 (continued) No.

Experimentala FT-IR

41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

B3LYP/6-31G(d,p) FT-Raman 677(m)

672(w) 631(w)

635(m)

566(w) 551(m)

470(w)

477(s) 446(w)

398(w) 378(m) 357(m)

293(m)

193(m) 143(s)

81(m)

Unscaled 704 688 670 643 606 599 581 557 550 537 509 479 469 460 441 424 410 390 376 348 331 316 286 278 265 261 247 227 214 192 171 161 115 106 94 71 56 41 38 22 14

Assignments based on PED (6-311G(d,p); P10%)b

B3LYP/6-311G(d,p)

Scaled 690 674 657 630 594 587 569 546 539 526 499 470 460 451 433 416 402 382 369 341 325 310 281 272 260 256 242 223 209 188 167 158 112 104 92 70 54 40 37 22 14

Unscaled 691 686 657 643 607 597 579 559 548 538 509 476 468 454 436 422 407 394 375 347 331 314 286 277 265 260 251 236 217 193 170 160 113 105 92 69 55 41 37 23 13

Scaled 677 672 644 630 595 585 568 547 538 527 499 467 458 445 428 414 399 386 368 340 324 307 280 272 260 254 246 232 213 189 167 156 111 103 90 67 54 40 36 23 13

bCCC(57) + tSN(18) bCCC(68) + tSN(23) bCCC(74) bCCO(78) bCCC(73) bCCO(70) dSO2(72) + wNH2(25) xNH(68) xNH(66) wSO2(44) + wNH2(20) bring(56) tCCl(15) xCC(64) xCC(64) + rSO2(27) xCC(62) xCC(61) bNCH(32) bCCO(42) rSO2(48) + tNH2(44) bNCO(38) + bCCl(26) bCCS(26) bCCS(20) bCSN(11) xCS(58) bCCN(12) xCO(26) tR3asymd(67) tR3asymd(65) tR3symd(55) tR3trigd(63) bCCl(25) tR2torsion1(95) tR2torsion2(96) tR1asymd(62) tR1symd(57) tR1trigd(61) sCACH2(67) sCACH2(65) sCACH3(52) sSANH2(88) sCASO2(82)

a

vs: Very strong, s: strong, m: medium, w: weak, vw: very weak. m: Stretching, ms: symmetric stretching, mas: asymmetric stretching, symd: symmetric deformation, asymd: asymmetric deformation, b: in-plane bending, x: out-ofplane bending, d: scissoring, w: wagging, t: twisting, r: rocking, s: torsion, trigd: trigonal, R1: ring1, R2: ring2, R3: ring 3, PED: Potential energy distribution. b

p-character on each natural atomic hybrid of the natural bond orbital is shown in Table 7. The larger the E(2) value, the more intensive is the interaction between electron donors and acceptors i.e., the more donation tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system. DFT (B3LYP/6-31G(d,p)) level computation is used to investigate the various second-order interactions between the filled orbitals of one subsystem and vacant orbitals of another subsystem, which is a measure of the delocalization or hyper-conjugation. The localized orbitals in the best Lewis structure can interact strongly. A filled bonding or lone pair orbital can act as a donor and an empty or filled bonding, anti-bonding or lone pair orbital can act as an acceptor. These interactions can strengthen and weaken bonds. A lone pair donor ? anti-bonding acceptor orbital interaction will weaken the bond associated with the anti-bonding orbital. Conversely, an interaction with a bonding pair as the acceptor will strengthen the bond. Strong electron delocalization in best Lewis structure will also show up as donor–acceptor interactions. This calculation is done by examining all possible interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’ (acceptor) non-Lewis NBOs. For CMDS, r(C20AC21) of the NBO conjugated with r(C22AC23) leads to an enormous stabilization

of 18.20 kJ/mol. This strong stabilization denotes the larger delocalization. This highest interaction around the ring can induce the large bioactivity in the compound.

Frontier molecular orbitals (FMOs) The highest occupied molecular orbitals (HOMOs) and the lowest-lying unoccupied molecular orbitals (LUMOs) are named as frontier molecular orbitals (FMOs). The FMOs play an important role in the optical and electric properties, as well as in quantum chemistry and UV–vis. spectra [49]. HOMO–LUMO orbitals are also called frontier orbitals as they lie at the outermost boundaries of the electrons of the molecules. The frontier orbital gap helps characterize the chemical reactivity and the kinetic stability of the molecule. A molecule with a small frontier orbital gap is generally associated with a high chemical reactivity, low kinetic stability and is also termed as soft molecule [49]. The 3D plots of the frontier orbitals HOMO and LUMO figures for the CMDS are shown in Fig. 4. The calculated energy values of HOMO and LUMO in ethanol are 5.8625 eV and 1.9609 eV and the frontier orbital energy gap value is 3.9016 eV for CMDS. Lower value in the HOMO and LUMO

11

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14 Table 6 Second order perturbation theory analysis of Fock matrix in NBO basis for CMDS. Donor (i) C1AC2

a b c

Type

r

ED/e 1.97340

C1AO8

r

1.99204

C1AN9 C2AC3

r r

1.98522 1.97118

C2AC7

r

1.97388

C3AC4

r

1.97179

C3AH40

r

1.97298

C4AC5

r

1.97723

C4AS11

r

1.97017

C5AC6

r

1.97700

C6AC7

1.97429

C6AH38

r p r

N9AH10 C20AC21

r r

1.98307 1.97379

1.97772

Acceptor (j) C2AC7 C3AC4 C1AC2 C2AC3 N17AC25 C2AC7 C3AC4 C3AH40 C4AS11 C1AN9 C2AC3 C2AC3 C4AC5 C2AC7 C4AC5 C3AC4 C5AC6 S11AO12 S11AO13 C4AC5 C4AS11 C7AH39 C5ACl27 C4AC5 C2AC7 C4AC5 C1AO8 C22AC23

Type

r



r



r r

r r r r r r r p r r r

ED/e

E(2)a (kJ mol1)

E(j)  E(i)b (a.u.)

F(i, j)c (a.u.)

0.01952 0.02580 0.07043 0.02368 0.03488 0.01952 0.02580 0.01674 0.18964 0.07653 0.02368 0.02368 0.03735 0.01952 0.03735 0.02580 0.02906 0.13589 0.15268 0.03735 0.18964 0.01308 0.02664 0.03735 0.01952 0.03735 0.39934 0.35173

1.51 3.09 2.83 3.58 3.65 3.69 3.88 1.07 3.72 1.50 3.89 3.31 5.22 3.86 4.20 4.92 3.40 2.43 2.85 4.71 4.08 1.75 4.51 24.21 3.55 4.61 3.36 18.20

1.16 1.15 1.46 0.37 1.21 1.23 1.21 1.10 0.85 1.15 1.22 1.25 1.23 1.08 1.05 1.26 1.25 1.02 1.02 1.22 0.87 1.15 0.86 0.24 1.05 1.02 1.32 0.27

0.038 0.053 0.058 0.036 0.060 0.060 0.061 0.031 0.052 0.038 0.048 0.058 0.072 0.058 0.059 0.070 0.058 0.046 0.050 0.068 0.055 0.040 0.055 0.070 0.054 0.061 0.060 0.063

E(2) means energy of hyper conjugative interaction (stabilization energy). Energy difference between donor and acceptor i and j NBO orbitals. F(i, j) is the Fock matrix element between i and j NBO orbitals.

Table 7 Percentage of s and p-character on each natural atomic hybrid of the natural bond orbital. Bond (AAB)

ED/energy (a.u)

EDA (%)

EDB (%)

s (%)

p (%)

C1AC2

0.6934 0.7205 0.5921 0.8058 0.6049 0.7963 0.7048 0.7094 0.7148 0.6993 0.7003 0.7148 0.7760 0.6307 0.7126 0.6983 0.7182 0.6943 0.7165 0.6976 0.6849 0.5989 0.7106 0.7036 0.5995 0.7876

48.09 – 35.06 – 36.59 49.68 – 51.09

51.91 – 64.94 – 63.41 – 50.32 – 48.91

49.05

50.95

60.02

39.78

50.78

49.22

51.58

48.42

51.34

48.66

46.91

53.09

50.50

49.50

35.94

64.06

35.47 30.05 33.21 41.82 30.97 38.32 34.12 36.35 35.05 35.64 35.56 38.21 28.08 99.95 38.87 37.33 22.93 25.18 38.86 35.34 23.61 18.87 31.05 29.90 27.55 24.28

64.49 69.90 66.66 58.06 68.92 61.64 65.84 63.61 64.91 64.31 64.41 61.75 71.87 0.05 61.09 62.63 76.99 73.39 61.10 64.62 76.20 80.58 68.88 70.02 70.89 75.58

C1AO8 C1AN9 C2AC3 C2AC7 C3AC4 C3AH40 C4AC5 C4AS11 C5AC6 C5ACl27 N9AN17 S11AO12

energy gap explains the eventual charge transfer interactions taking place within the molecule, which influences the biological activity of the molecule. The narrow energy gap between HOMO and LUMO facilitates intra molecular charge transfer which makes the material to be NLO active [50]. Analysis of the wavefunction indicates that the electron absorption corresponds to the transition

from the ground to the first excited state and is mainly described by one-electron excitation from the HOMO to the LUMO. All the HOMO and LUMO have nodes. The positive phase is red and the negative one is green. According to Fig. 4, the HOMO a charge density localized over the rings (rings 2 and 3) of the molecule expect ring 1, SO2 and NH2 groups, but the LUMO is characterized by a charge distribution on ring 1, chlorine atom and SO2 group, expect NH2 group. By using HOMO and LUMO energy values for a molecule, the chemical hardness, electronegativity, chemical potential and electrophilicity index of the molecule were calculated. The calculated results are presented in Table 8. Considering the chemical hardness, if a molecule has large HOMO–LUMO gap, it is a hard molecule or small HOMO–LUMO gap it is a soft molecule. One can also relate the stability of molecule to hardness, which means that the molecule with least HOMO–LUMO gap means it is more reactive. UV–vis spectral analysis The UV spectrum of CMDS measured in ethanol was shown in Fig. 5 and comparison graph was shown in Fig. S3. In an attempt to understand the nature of electronic transitions in terms of their energies and oscillator strengths, TD-DFT calculations involving configuration interaction between the singly excited electronic states was performed while taking solvent effect into account. The calculated excitation energies, oscillator strengths (f) and wavelengths (k) are given in Table 9. Calculations of molecular orbital geometry show that the visible absorption maxima of this molecule correspond to the electron transition between frontier orbitals such as translation from HOMO to LUMO. The maximum absorption peak (kmax) observed in UV–vis spectrum corresponds to vertical transitions according to Frank–Condon principle. It could be seen that low energy absorption found at 287 nm and

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S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14

Fig. 5. UV absorption spectrum of CMDS in ethanol.

Fig. 4. The molecular orbitals and energies for the HOMO and LUMO of CMDS in ethanol.

240 nm belongs to the dipole-allowed n–p and p–p transition from HOMO to LUMO, respectively. The kmax is a function of substitution, the stronger the donor character of the substitution, the more electrons pushed into the molecule, the larger kmax. As can be seen from Table 9, TD-DFT/6-311G(d,p) method predicts two electronic transitions at kcal = 270.07 nm with f = 0.0040, and kcal = 252.40 nm with f = 0.0570. These values may be slightly shifted by solvent effects. Molecular electrostatic potential (MEP) MEP and electrostatic potential are useful quantities to illustrate the charge distributions of molecules and used to visualize variably charged regions of a molecule. Therefore, the charge distributions can give information about how the molecules interact with another molecule. MEP is widely used as a reactivity map displaying most probable regions for the electrophilic attack of charged point-like reagents on organic molecules [51]. The molecular electrostatic potential V(r) that is created in the space around a molecule by its nuclei and electrons is well established as a guide to molecular reactive behavior. It is defined by:

VðrÞ ¼

X

Z A =ðRA  rÞ 

Z

qðr0 Þ=ðr0  rÞ dr

ð8Þ

A

in which ZA is the charge of nucleus A, located at RA, q(r0 ) is the electronic density function for the molecule and r0 is the dummy Table 8 Calculated energy values of CMDS using TD-DFT/6-311G(d,p). Parameters (eV)

Gas phase

Ethanol

Etotal ELUMO+2 ELUMO EHOMO EHOMO1 DE(LUMO+2HOMO) DE(LUMOHOMO) DE(LUMOHOMO1) Chemical hardness (h) Electronegativity (v) Chemical potential (l) Electrophilicity index (x)

50827.8790 1.5693 1.9911 5.9183 7.0614 4.3490 3.9272 5.0703 1.9636 3.9547 3.9547 3.9823

50828.5069 1.4721 1.9609 5.8625 7.0122 4.3903 3.9016 5.0513 1.9508 3.9117 3.9117 3.9218

integration variable [51,52]. At any given point r(x, y, z) in the vicinity of a molecule, the MEP, V(r) is defined in terms of the interaction energy between the electrical charge generated from the molecule electrons and nuclei and a positive test charge (a proton) located at r [53]. The MEP is related to electron density and a very useful descriptor for determining sites for electrophilic attack and nucleophilic reactions as well as hydrogen-bonding interactions [54,55]. To predict reactive sites for electrophilic and nucleophilic attack for the investigated molecule, the 3D Molecular electrostatic potential surface (MEPs) and 2D MEPs contour map for the title molecule are shown in Figs. 6 and S4. The different values of the electrostatic potential at the surface are represented by different colors. Potential increases in the order red < orange < yellow < green < blue. The negative (red, orange and yellow) regions of the MEP are related to electrophilic reactivity. The maximum positive region is localized on the NAH bonds, indicating a possible site for nucleophilic attack. The MEP map shows that the negative potential sites are on electronegative oxygen atoms (O12, O13 and O8) and the positive potential sites are around the hydrogen atoms. These sites give information about the region from where the compound can have intermolecular interactions. This predicted the most reactive site for both electrophilic and nucleophilic attack. Thermodynamic properties The thermodynamic parameters supply helpful and extra information about the title molecule. Therefore, some values (such as zero-point vibrational energy, thermal energy, specific heat capacity, rotational constants, entropy and dipole moment) of the studied molecule by DFT/B3LYP 6-31G(d,p) and 6-311G(d,p) method at 298.15 K in ground state are listed in Table S1. The global minimum energy values obtained for structure optimization of B3LYP with 6-31G(d,p) and 6-311G(d,p) basis sets are 1867.59012645 and 1867.87542841 Hartree, respectively. On the basis of vibrational analysis at B3LYP/6-31G(d,p) level, the standard statistical thermodynamic functions: heat capacity (C), entropy (S) and enthalpy (H) for the title compound were obtained from the theoretical harmonic frequencies and listed in Table 10. From Table 10, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 K to 700 K due to the fact that the molecular vibrational intensities increase with temperature [56]. The correlation equations between heat capacity, entropy, enthalpy and temperatures were fitted by quadratic formulas, and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9997, 1.0000 and 0.9998, respectively. The corresponding fitting equations are as follows and the correlation graphics of those are shown in Fig. 7.

C ¼ 1:7092 þ 0:3248T  14:9379  105 T 2

ðR2 ¼ 0:9997Þ

ð9Þ

13

S. Muthu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 1–14 Table 9 Experimental and calculated absorption wavelengths (k), energies (E) and oscillator strengths (f) of CMDS in ethanol and gas phase. Experimental

TD-DFT/6-311G(d,p)

Ethanol k (nm)

Ethanol E (eV)

k (nm)

5.1454

370.61 318.60 270.07 269.62 265.33 252.40

287

240

Gas

(95 ? 96) (95 ? 97) (94 ? 96) (92 ? 96) (95 ? 98) (93 ? 97)

E (eV)

f

k (nm)

3.3454 3.8915 4.5909 4.5985 4.6729 4.9121

0.0256 0.0120 0.0040 0.0146 0.0428 0.0579

367.19 321.59 280.94 268.99 264.97 254.40

(95 ? 96) (95 ? 97) (93 ? 96) (94 ? 96) (95 ? 98) (93 ? 97)

E (eV)

f

3.3766 3.8553 4.4132 4.6093 4.6792 4.8735

0.0201 0.0105 0.0048 0.0103 0.0287 0.0107

Fig. 6. The 3D molecular electrostatic potential surface for CMDS. Fig. 7. Correlation graphic of heat capacity, entropy, enthalpy and temperature for CMDS. Table 10 Temperature dependence of thermodynamic properties of at B3LYP/6-311G(d,p). T (K)

C (cal mol1 K1)

S (cal mol1 K1)

H (kcal mol1)

100 150 200 250 300 350 400 450 500 550 600 650 700

33.957 46.996 59.82 72.55 85.053 97.014 108.149 118.303 127.444 135.624 142.932 149.474 155.349

99.502 116.55 132.401 147.562 162.263 176.587 190.544 204.113 217.269 229.996 242.289 254.151 265.595

2.264 4.388 7.159 10.568 14.609 19.263 24.495 30.260 36.507 43.187 50.254 57.666 65.389

S ¼ 66:3139 þ 0:3461T  8:8032  105 T 2

H ¼ 1:5252 þ 0:0236T þ 10:3721  105 T 2

ðR2 ¼ 1:0000Þ

ð10Þ

ðR2 ¼ 0:9998Þ ð11Þ

All the thermodynamic data supply helpful information for the further study on the CMDS. They can be used to compute the other thermodynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermo chemical field [56]. It must be noticed that all thermodynamic calculations were done in gas phase and they could not be used in solution.

Conclusion FT-IR, FT-Raman, UV spectra and DFT quantum chemical calculations studies were performed on CMDS, in order to identify its structural and spectroscopic features. Several properties were carried out using experimental techniques and tools derived from DFT. On the basis of experimental results and PED calculations, assignments of all the fundamental vibrational frequencies were done. A good correlation between the observed and scaled wavenumbers was obtained for the title compound. Scaled results seemed to be in good agreement with experimental ones. Absorption maxima (kmax) of CMDS was calculated by TD-DFT method and compared with experimental UV–vis spectra. HUMO and LUMO orbitals have been visualized. It has been conclude that the lowest singlet excited state of the title molecule is mainly derived from the HOMO ? LUMO electron transition. The electric dipole moment, polarizability, mean polarizability and the first order hyperpolarizability of the title compound were calculated. The correlations of the statistical thermodynamics according to temperature were also presented. We hope our results will be of assistance in the quest of the experimental and theoretical evidence for the title molecule in reaction intermediates, nonlinear optical and photoelectric materials and will also be helpful for the design and synthesis of new materials.

Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2013.10.115.

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