NLMO analysis of 2-bromo-5-nitrothiazole

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Quantum chemical calculations, vibrational studies, HOMO–LUMO and NBO/NLMO analysis of 2-bromo-5-nitrothiazole E. Gobinath a, R. John Xavier b,⇑ a b

Department of Physics, Jayaram College of Engineering and Technology, Tiruchirappalli 621 014, India PG and Research Department of Physics, Periyar EVR College(Autonomous), Tiruchirappalli 620 023, India

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

" The FT-IR and FT-Raman spectra of

" " " "

the title compound have been recorded. Optimized geometry, vibrational frequencies are obtained. The first hyperpolarizability has been determined. The HOMO and LUMO energies have been calculated. Stability of the molecule has been analyzed using NBO and NLMO analysis.

a r t i c l e

i n f o

Article history: Received 15 August 2012 Received in revised form 10 November 2012 Accepted 16 November 2012 Available online 5 December 2012 Keywords: 2-Bromo-5-nitrothiazole HF B3LYP HOMO–LUMO NBO NLMO

a b s t r a c t The complete vibrational assignment and analysis of the fundamental modes of 2-bromo-5-nitrothiazole (BNT) was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the ab initio HF and DFT–B3LYP gradient calculations employing 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy have been calculated for the molecule. HOMO–LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of BNT have been computed using B3LYP quantum chemical calculation. Ó 2012 Elsevier B.V. All rights reserved.

Introduction Thiazole is a heterocyclic compound that contains both sulfur and nitrogen. The thiazole ring is notable as a component of the vitamin thiamine (B1). The compounds containing thiazole ring have shown useful biological properties and have been developed as fungicides, herbicides, or plant growth regulators. Nitrothiazole and their derivatives have attracted the attention of researchers from many fields due to their wide variety of applications. The nitro group of the nitrothiazole ring moiety represents the chemical ⇑ Corresponding author. Tel.: +91 431 2705674. E-mail address: [email protected] (R.J. Xavier). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.11.066

structure responsible for their excellent antibacterial activities [1]. Different nitrothiazole derivatives display pronounced antibacterial properties against aerobic as well as anaerobic bacteria [2]. Some of them are highly active against 19 microaerophilic campylobacters including campylobacter jejuni and campylobacter coli [3]. Nitrothiazole derivatives, such as niridazole exert pronounced activities against several trichomonad strains when tested under anaerobic conditions comparable to those of the nitroimidazole derivatives [4]. 2-Acetamido-5-nitrothiazole is found to be capable of protecting mice against experimental protozoal infections, including Trichomonas foetus and Trichomonas vaginalis [5,6]. Besides, derivatives of 2-aminothiazole have a long history of use as heterocyclic diazo components for disperse dyes and they can be

395

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402

made as a prominent replacement for blue anthraquinone colorants because of their appreciable properties [7–9]. Recently, Arjunan et al. has made spectroscopic investigation on 2-amino-4methylbenzothiazole [10]. Literature survey reveals that to the best of our knowledge, no ab initio DFT frequency calculations of the title compound 2-bromo-5-nitrothiazole (BNT) have been reported so far. The lack of literature in spectroscopy and the interesting features of the derivatives of thiazoles and nitrothiazoles led to the present investigation aiming at studying the molecular structure, geometrical parameters, vibrational wavenumbers, modes of vibrations, determination of first order hyper polarizability, important thermodynamic properties, and the Natural Bond Orbital (NBO)/Natural Localized Molecular Orbital (NLMO) analysis which explains the most important orbital interactions of the title compound. The Frontier orbital analysis has also been made. Experimental details The fine polycrystalline sample of 2-bromo-5-nitrothiazole was purchased from Alfa Aesar chemical company, UK with a stated purity of 98% and it was used as such without further purification. The room temperature Fourier transform infrared spectra of the title compound was measured in the region 4000–400 cm1 at a resolution of ±1 cm1 using a JASCO FT/IR-6300 spectrometer. KBr pellets were used in the spectral measurements. Boxcar apodization was used for 250 averaged interferograms collector for both the sample and background. The FT-Raman spectrum of the title compound was recorded on a BRUKER RFS 100/S model interferometer equipped with FRA-106 FT-Raman accessory in the 3500–500 cm1 stokes region using the 1064 nm line of Nd: YAG laser for excitation, operating at 150 mW power. The reported wave numbers are believed to be accurate within ±4 cm1.

Fig. 1. Molecular structure of 2-bromo-5-nitrothiazole along with numbering of atoms.

HF and DFT/B3LYP with 6-311++G(d,p) basis set for BNT are calculated as 3342.6469 and 3347.2119 Hartrees, respectively. The optimized geometrical parameters of BNT obtained by HF and DFT/B3LYP with 6-311++G(d,p) basis set are presented in Table 1 by comparing with the experimental X-ray diffraction [17] bond

Table 1 Experimental (XRD) and optimized geometrical parameters (bond length, bond angle, dihedral angle) of 2-bromo-5-nitrothiazole obtained by HF and B3LYP methods. Experimentala

Parameters

HF 6-311G++(d,p)

B3LYP 6-311++G(d,p)

o

Computational details The quantum chemical calculation employed vibrational spectroscopic studies are of paramount importance in the understanding of fundamental modes of vibrations of the chemical compounds. The molecular geometry optimizations, calculations of energy, vibrational frequencies, IR intensities and Raman activities were carried out for BNT with the GAUSSIAN 09 software package [11] using DFT/B3LYP functional [12,13] combined with the standard 6-311++G(d,p) basis set. Initial geometry generated from the standard geometrical parameters was minimized without any constraint on the potential energy surface at Hartree–Fock level adopting the standard 6-311++G(d,p) basis set. This geometry was then re-optimized again at DFT level employing the Becke 3LYP keyword, which invokes Becke’s three parameter- hybrid method [12] using the correlation function of Lee et al. [13] implemented with the same basis set for better description of the bonding properties. The optimized structural parameters were used in the vibrational frequency calculations. Further, the transformations of the force field, and the subsequent normal coordinate analysis including the least square refinement of the scaling factors, calculation of the total energy distribution (TED) and the prediction of IR and Raman intensities were done on a PC with the MOLVIB Program (Version V7.0-G77) written by Sundius [14–16]. Results and discussion Molecular geometry and structural properties The molecular structure and numbering of the atoms of BNT are shown in Fig. 1. The global minimum energies obtained by ab initio

Bond length (A ) S1–C2 1.773 S1–C5 1.739 C2–N3 1.314 C2–Br6 – N3–C4 1.391 C4–C5 1.408 C4–H7 – C5–N8 – N8–O9 – N8–O10 – Bond angle (o) S1–C2–N3 C2–N3–C4 N3–C4–C5 S1–C5–C4 C2–S1–C5 S1–C2–Br6 N3–C2–Br6 N3–C4–H7 C5–C4–H7 C4–C5–N8 S1–C5–N8 C5–N8–O9 C5–N8–O10 O9–N8–O10

115.7 110.2 115.8 109.6 88.7 – – – – – – – – –

Dihedral angle (o) C5–S1–C2–Br6 C2–S1–C5–N8 Br6–C2–N3–C4 C2–N3–C4–H7 N3–C4–C5–N8 H7–C4–C5–S1 S1–C5–N8–O9 C4–C5–N8–O10

– – – – – – – –

For numbering of atoms refer 1. a Values are taken from Ref. [17].

1.725 1.729 1.272 1.870 1.368 1.341 1.071 1.434 1.186 1.188

1.745 1.741 1.297 1.884 1.366 1.366 1.081 1.440 1.225 1.228

117.12 110.42 114.35 111.62 86.47 120.19 122.69 120.23 125.42 126.26 122.13 117.28 116.72 126.00

116.80 110.48 114.69 111.45 86.58 120.13 123.07 120.66 124.65 126.92 121.63 117.29 116.89 125.82

180.00 180.00 180.00 180.00 180.00 180.00 180.00 180.00

180.00 180.00 180.00 180.00 180.00 180.00 180.00 180.00

396

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402

lengths and angles of a compound having similar structure. In the present work, geometry optimization parameters for BNT have been employed without any symmetry constrain. From Table 1, it is found that the bond lengths and bond angles calculated by DFT/B3LYP and HF methods are consistent with experimental values. The internal coordinates and local symmetry coordinates of BNT are shown in Tables 2 and 3, respectively. The thermodynamic properties like heat capacity, entropy, rotational constants, dipole moment and zero point vibrational energy (ZPVE) of the title compound have also been computed at ab initio HF and DFT-B3LYP levels using 6-311++G(d,p) basis set and they are presented in Table 4. The differences in the values obtained by both the methods are marginal. Since the charge distribution on the molecule has an important influence on the vibrational spectra, the natural population analysis (NPA) charge distribution of BNT was calculated by HF/6311++G(d,p) and B3LYP/6-311++G(d,p) with basis set. From the NPA values listed in Table 5, we can observe the electropositive nature in hydrogen and bromine and sulfur atoms. The nitrogen atom N3 is electronegative since it is bonded to carbon atoms on either side in the heterocyclic ring. On contrary, the nitrogen atom N8 exhibits electropositivity since it is bonded to oxygen atoms O9 and O10 on either side.

Table 3 Definition of local symmetry co-ordinates of 2-bromo-5-nitrothiazole.

a b

No.

Symbol

Definitiona,b

1–2 3 4 5 6–8 9

SC CBr CH CC CN NO2 ss

r1, r2 R3 p4 P5 q6, q7, q8

10

NO2 ass

11 12 13

R bend 1 R1 bend 2 bCBr

14

bCH

15

bCN

16

NO2 rock

17

NO2 twist

18

NO2 sciss

19 20 21 22 32 33

xCBr xCH xCN t R torsion 1 t R1 torsion 2 NO2 wag

pffiffiffi ðQ 9  Q 10Þ= 2 pffiffiffi ðQ 9 þ Q 10Þ= 2 (b11 + a(b12 + b15) + b(b13 + b14)) (ab) (b12–b15) + (1a) (b13–b14) pffiffiffi ða16  a17 Þ= 2 pffiffiffi ðr18  r19 Þ= 2 pffiffiffi ð20  21 Þ= 2 pffiffiffi ðd22  d23 Þ= 2 pffiffiffi ðd22 þ d23 Þ= 2 pffiffiffi ð2d24  d22  d23 Þ= 6

x25 x26 x27 b(s28 + s32) + a(s29 + s31) + s30 (ab) (s31s29) + (1a) (s32s28) s33

The internal coordinates used here are defined in Table 1. a = cos144°, b = cos72°.

First hyperpolarizability The potential application of the title compound in the field of nonlinear optics (NLO) demands the investigation of its structural and bonding features contributing to the hyperpolarizability enhancement, by analyzing the vibrational modes using IR and Raman spectroscopy. Many organic molecules, containing conjugated electrons are characterized by large values of molecular first hyper polarizability, were analyzed by means of vibrational spectroscopy [18–20]. The B3LYP/6-311++G(d,p) method has been used for the prediction of first hyperpolarizability. First hyperpolarizability is a third rank tensor that can be described by 3  3  3 matrix. The 27 components of 3D matrix can be reduced to 10 components due to the Kleinmann symmetry [21,22]. The output from Gaussian

09 provides 10 components of this matrix as bxxx, bxxy, bxyy, byyy, bxxz, bxyz, byyz, bxzz, byzz, bzzz, respectively and they are given in Table 6. The components of the first hyperpolarizability can be calculated using the following equations.

b ¼ b2x þ b2y þ b2z where

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bz ¼ bzzz þ bxxz þ byyz

Table 2 Definition of internal co-ordinates of 2-bromo-5-nitrothiazole. No

Symbol

Type

Definition

Stretching 1–2 3 4 5 6–8 9–10

ri Ri Pi Pi qi Qi

S–C C–Br C–H C–C C–N N–O

S1–C2, S1–C5 C2–Br6 C4–H7 C4–C5 C2–N3, C4–N3, C5–N8 N8–O9, N8–O10

bi

Ring SCBr NCBr NCH CCH CCN SCN CNO ONO

S1–C2–N3, C2–N3–C4, N3–C4–C5, C4–C5–S1, C5–S1–C2 S1–C2–Br6 N3–C2–Br6 N3–C4–H7 C5–C4–H7 C4–C5–N8 S1–C5–N8 C5–N8–O9, C5–N8–O10 O9–N8–O10

xi

CBr CH CN

C2–Br6–S1–N3 C4–H7–N3–C5 C5–N8–C4–S1

ti ti

s Ring s C–NO2

S1–C2–N3–C4, C2–N3–C4–C5, N3–C4–C5–S1, C4–C5–S1–C2, C5–S1–C2–N3 C5–N8–O9–O10

Bending 11–15 16 17 18 19 20 21 22–23 24 Out-of-plane bending 25 26 27 Torsion 28–32 33

ai ai ri ri 2i 2i di di

xi xi

For numbering of atoms refer Fig. 1.

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402 Table 4 Theoretically computed thermodynamic parameters of 2-bromo-5-nitrothiazole calculated at HF and B3LYP methods using 6-311++G(d,p) basis set. Parameter

HF 6-311++G(d,p)

B3LYP 6-311++G(d,p)

Zero-point vibrational Energy (kJ/mol) Rotational constants (GHz)

137.540 3.85322 0.45294 0.40530

124.036 3.70976 0.44487 0.39723

37.529 0.889 0.889 35.751

34.601 0.889 0.889 32.823

Thermal energy (kJ/mol) Total Translational Rotational Vibrational

Molar capacity at constant volume (calmol1Kelvin1) Total 25.027 Translational 2.981 Rotational 2.981 Vibrational 19.066

26.848 2.981 2.981 20.886

Entropy (calmol1Kelvin1) Total Translational Rotational Vibrational

89.934 41.900 30.498 17.537

91.987 41.900 30.573 19.515

2.8561 0.1720 0.0000 2.8612

2.9422 0.0572 0.0006 2.9427

Dipole moment (Debye)

lx ly lz ltotal

Table 5 The NPA charge distribution of 2-bromo-5-nitrothiazole calculated by HF and B3LYP methods with 6-311++G(d,p) basis set. ATOM

Methods/basis sets

S1 C2 N3 C4 C5 Br6 H7 N8 O9 O10

HF 6-311++G(d,p)

B3LYP 6-311G++(d,p)

0.48173 0.00195 0.54454 0.10112 0.15950 0.15642 0.22732 0.61385 0.43671 0.44163

0.50603 0.07563 0.47545 0.02935 0.12483 0.17546 0.23885 0.46614 0.36480 0.37513

397

1030 esu, which is relatively much higher than that of Urea and thus the title compound possesses considerable NLO properties. Vibrational analysis and theoretical prediction of spectra The molecular structure of BNT belongs to point group C1 including only identity operation symmetry element, thus all the frequency modes (Cvibration) are produced in A species. The molecule consists of 10 atoms and expected to have 24 normal modes of vibrations of the same A species under C1 symmetry. These modes are found to be active both in the Raman scattering and infrared absorption. For visual comparison, the observed and calculated (simulated) FTIR and FT-Raman spectra of BNT are presented in a common frequency scale in Figs. 2 and 3, respectively. Normally, the vibrational frequencies obtained by quantum chemical calculations with unscaled ab initio and DFT force field are generally greater than the experimental values due to the facts of the electron correlation approximate treatment, the anharmonicity effect and basis set deficiency, etc., [23]. In order to improve the calculated values in agreement with the experimental values, it is necessary to scale down the calculated harmonic frequencies. After scaling, the theoretical frequencies will match well with the experimental ones. Table 7 gives the observed and calculated frequencies and their assignments along with their TED, theoretical IR intensities, Raman activities and force constants of BNT calculated by HF and B3LYP methods using 6-311++G(d,p) basis set. Nitro group vibrations One can expect six internal modes of vibrations for NO2 group of atoms, namely, the asymmetric stretching, symmetric stretching, the symmetric planar deformation or scissoring, the antisymmetric planar deformation or rocking, the symmetric non-planar deformation or wagging and the anti-symmetric non-planar deformation or torsion modes of vibrations. Aromatic nitro compounds have strong absorptions due to asymmetric and symmetric stretching vibrations of the NO2 group at 1570–1485 and 1370–1320 cm1, respectively, Hydrogen bonding has a little effect on the NO2 asymmetric stretching vibrations [24,25]. In BNT, an IR active band at 1570 cm1 and a Raman active band at 1365 cm1 have been assigned to NO2 asymmetric and symmetric stretching modes of vibrations, respectively. A Raman band at 759 cm1, and an IR band

Table 6 All ‘b’ components and total first polarizability of 2-bromo-5-nitrothiazole calculated by B3LYP method with 6-311++G(d,p) basis set. Parameters

Value

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz b total

71.898 196.520 390.154 581.368 0.106 0.163 0.293 2.731 42.782 0.039 7.356  1030 esu

Urea is one of the prototypical molecules used in the study of the NLO properties of molecular systems. Therefore it was used frequently as a threshold value for comparative purposes. The calculated value of b for the title compound is around 7.356 

Fig. 2. Comparison of observed and calculated IR spectra of 2-bromo-5-nitrothiazole (a) observed; (b) calculated with HF/6-311++G(d,p); (c) calculated with B3LYP/ 6-311++G(d,p).

398

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402

Carbon–sulfur vibrations In general, the assignment of band due to the C–S stretching vibration in different compounds is difficult in the infrared, since the band is of variable intensity and may be found over the wide region 1035– 245 cm1, whereas, C–S stretching vibration results in strong bands in Raman spectra which are normally easy to identify [26]. The C–S group is less polar compared to carbonyl links and has a considerably weaker band. In consequence, the band is not intense, and it falls at lower frequencies, where it is much more susceptible to coupling effects and identification is therefore difficult and uncertain. The absorption of C–S group with other substituent usually appears between 1250 and 1020 cm1 [27]. Considerations of these factors lead to assign the FT-IR bands at 1186 and 1116 cm1 and Raman active bands at 1193 and 1122 cm1 in BNT to C–S vibrations. The in-plane and out-of-plane bending vibrations of C–S group are found well within the characteristic region. The calculated values are also found in line with the observed frequencies.

Fig. 3. Comparison of observed and calculated Raman spectra of 2-bromo-5nitrothiazole (a) observed; (b) calculated with HF/6-311++G(d,p); and (c) calculated with B3LYP/6-311++G(d,p).

at 591 cm1 are assigned to NO2 scissoring and NO2 rocking mode of vibrations. They are in line with the computed wavenumbers by HF and B3LYP methods. Similarly, the NO2 wagging and twisting modes are also found to be in good agreement and they are given in Table 7.

Carbon–bromine vibrations The vibrations belonging to the bond between the ring and bromine atom is important as mixing of vibrations is possible due to the presence of heavy atom [28–30]. Bromine compounds normally absorb in the region of 650–450 cm1 due to the C–Br stretching vibrations [31,32]. In BNT, an IR active band at 478 cm1 is assigned C–Br stretching vibrations. The in-plane bending mode of vibration has been assigned to an IR active band at 446 cm1. The out-of-plane bending mode is assigned to a Raman band at 116 cm1. All these bands are found to be in agreement with the calculated wave numbers, as shown in Table 7.

Table 7 Experimental and calculated(unscaled and scaled) HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) level vibrational frequencies (cm1), IR intensity (kM mol1), Raman activity (Å amu1), force constant (mdyne Å1) and probable assignments of 2-bromo-5-nitrothiazole. No

Symm. species

Experimental frequencies

HF 6-311++G(d,p)

Characterization of normal modes with PED (%)

FTIR

FTRaman

Un Scaled

Scaled

IR intensity

Raman activity

Force constant

Un scaled

Scaled

IR intensity

Raman activity

Force constant

87.24 23.34 70.86 118.16 399.19 97.33 26.38 7.48 1.88 2.001

6.77 19.06 9.04 14.90 12.34 3.11 1.79 4.31 6.36 0.69

1 2 3 4 5 6 7 8 9 10

A A A A A A A A A A

3079 1570 – – – 1339 1186 1116 1012 908

3083 – 1540 1410 1365 1334 1193 1122 – 911

3414 1806 1735 1620 1577 1432 1267 1250 1116 1044

3097 1598 1562 1423 1379 1353 1208 1136 1324 927

4.30 636.28 22.43 259.61 524.98 17.85 37.64 60.48 81.47 8.56

74.69 12.39 72.39 39.08 296.20 21.97 14.65 23.47 7.51 4.13

7.55 25.39 12.84 21.35 17.70 3.02 5.35 2.18 8.63 0.92

3238 1581 1532 1419 1360 1312 1186 1129 1004 908

3084 1576 1544 1415 1369 1342 1198 11120 1016 913

5.26 284.85 19.09 149.44 566.77 90.45 36.77 27.45 94.49 10.58

11 12 13

A A A

810 – 739

816 759 –

933 826 825

829 771 748

63.80 6.53 19.33

6.58 4.26 1.50

6.55 2.89 4.89

829 748 723

817 763 742

38.49 7.27 9.71

14.97 5.39 0.64

5.35 2.40 3.90

14 15 16

A A A

– 591 –

656 – 504

724 651 553

667 612 524

1.64 11.49 0.91

9.87 0.66 4.46

5.12 1.65 2.09

657 596 502

660 596 510

0.47 6.38 0.30

11.19 0.21 4.75

4.28 1.27 1.71

17 18 19 20 21

A A A A A

478 446 – – –

– – 288 260 249

518 491 306 296 276

488 462 296 271 258

7.01 9.34 0.75 3.98 5.28

0.73 0.23 1.64 0.36 3.61

0.71 2.09 0.93 0.60 0.87

474 444 278 260 251

481 451 291 263 252

5.88 6.58 0.20 3.73 5.30

0.33 0.21 0.80 0.12 4.10

0.67 1.71 0.80 0.46 0.70

22

A

–

145

152

156

2.44

1.35

0.24

137

149

1.87

1.26

0.19

23 24

A A

– –

116 78

102 81

128 86

2.35 0.05

0.07 0.26

0.14 0.05

92 76

120 80

2.01 0.08

0.00 0.23

0.11 0.04

Abbreviations: m-stretching; ss-symmetric stretching; ass-assymetric stretching; Rbend – ring deformation; t-torsion. For the notations used, see Table 2.

CH (100) NO2 ass (98) CC (87), CN(11) CN(86), bCH(10) NO2 ss (96) CN(81), CS(17) CS(80), CBr(11) CS(83), CN(13) CN(87) Rbend1 (77), CH (18) b CH (72), CN (21) NO2 sciss (89) Rbend 2 (73), Rbend (21) bCN (70), CS (19) NO2 rock (69) tRtorsion1(65), xCBr (21) xCBr (79) bCBr (60), CN (12) NO2 wag (71) xCH (53) tRtorsion2(57), tRtorsion1(27) xCN (53), tRtorsion1(21) xCBr (51), xCH (27) NO2 twist (61)

399

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402

HOMO–LUMO analysis The most important orbitals in a molecule determine the way the molecule interacts with other species are the frontier molecular orbitals, called highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). They are the key parameter in determining molecular properties, molecular electrical transport properties [10,33,34]. Moreover, the Eigen values of HOMO (p donor) and LUMO (p acceptor) and their energy gap reflect the chemical activity of the molecules. Recently, the energy gap between HOMO and LUMO has been used to prove the bioactivity from intra-molecular charge transfer (ICT) [35,36]. The molecular orbital (MO) calculations indicate that the title compound BNT has 50 occupied MOs. The energies of HOMO, LUMO, LUMO+1 and HOMO1 and their orbital energy gaps have been calculated using B3LYP/6311++G(d,p) method and the pictorial illustration of the frontier molecular orbitals and their respective positive and negative regions are shown in Fig. 4. From Fig. 4, it is clear that HOMO is mainly localized over the five membered nitro thiazole ring and the LUMO is localized over the NO2 and also over the C4–C5 bond in the heterocyclic ring. It implies that an electron density transfer to the NO2 group of atoms from the thiazole ring take place. The frontier molecular orbitals are mainly composed of p atomic orbital, so, electronic transitions from the HOMO to the LUMO are mainly derived from the electronic transitions of p–p.

Table 8 Significant donor–acceptor interactions of 2-bromo-5-nitrothiazole and their second order perturbation energies. Donor NBO (i)

Acceptor NBO (j)

E(2)a (kcal/mol)

Ej–Eib (a.u)

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

BD (1) S1–C2 BD (1) S1–C5 BD (2) C2–N3 BD(1) N3–C4 BD (2) C4–C5

BD (1) C5–N8 BD (1) C2–Br6 BD (2) C4–C5 BD (1) C2–Br6 BD (2) C2–N3 BD (2) N8–O9 LP (3) O10 BD (2) N8–O9 BD (2) C2–N3 BD (2) C4–C5 BD (1) S1–C2 BD (1) C4–C5 BD (1) S1–C2 BD (1) C2–N3 BD (2) C2–N3 BD (1) C5–N8 BD (1) N8–O10 BD (1) C5–N8 BD (1) N8–O9 BD (2) N8–O9 BD (2) C4–C5 BD (2) C4–C5

5.48 5.91 19.08 7.82 10.71 22.09 11.86 8.32 32.43 19.93 15.38 5.34 5.56 5.19 15.29 11.82 18.82 10.50 19.06 162.95 88.63 19.04

1.00 0.77 0.35 0.88 0.27 0.17 0.18 0.32 0.23 0.26 0.55 0.93 0.47 0.84 0.26 0.58 0.71 0.59 0.72 0.140 0.03 0.13

0.067 0.060 0.076 0.074 0.051 0.063 0.077 0.055 0.077 0.066 0.082 0.065 0.046 0.059 0.061 0.074 0.105 0.070 0.106 0.138 0.076 0.064

BD (2) N8–O9 LP (2) S1 LP (1) N3 LP (2) Br6 LP (3) Br6 LP (2) O9 LP (2) O10 LP (3) O10 BD (2) C2–N3 BD (2) N8–O9 a b c

E(2) means energy of hyperconjucative interactions. 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.

LUMO +1

LUMO

HOMO

∆E = EHOMO - ELUMO = 0.13028a.u

HOMO−1

Fig. 4. Plots of the frontier orbitals of 2-bromo-5-nitrothiazole by B3LYP/6-311++G(d,p), with energies.

400

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402 Table 9 Occupancy, percentage of p character of significant natural atomic hybrid of the Natural Bond Orbital (NBO) of 2-bromo-5-nitrothiazole calculated at B3LYP level using 6-311++G(d,p) basis set. Bond

ED (e)

Hybrid

Atom

p (%)

BD (1) S1–C2

1.97844

0.6837 (sp4.96) S + 0.7298 (sp2.02) C

S1 C2 S1 C5 C2 N3 C2 N3 C2 Br6 N3 C4 C4 C5 C4 C5 C4 H7 C5 N8 N8 O9 N8 O9 N8 O10 S1 S1 N3 Br6 Br6 Br6 O9 O9 O10 O10 O10 S1 C2 S1 C5 C2 N3 C2 N3 C2 Br6 N3 C4 C4 C5 C4 C5 C4 H7 C5 N8 N8 O9 N8 O9 N8 O10

63.87 66.81 82.17 71.90 61.52 61.88 99.92 99.75 71.35 86.67 68.22 69.93 62.87 57.37 99.91 99.98 67.01 0.06 70.52 64.41 67.69 75.46 99.75 99.85 75.70 67.95 33.48 99.60 69.15 12.99 99.60 99.96 24.36 99.87 24.41 99.57 99.88 82.66 66.81 82.17 71.90 61.52 61.88 99.92 99.75 71.35 86.67 68.22 69.93 62.87 57.37 99.91 99.98 67.01 0.06 70.52 64.41 67.69 75.46 99.75 99.85 67.95 75.70

4.78

2.58

BD (1) S1–C5

1.96896

0.6838 (sp

BD (1) C2–N3

1.99113

0.6342 (p1.60) C + 0.7732 (sp1.63) N

BD (2) C2–N3

1.86118

0.6701 (p1.00) C + 0.7423 (p1.00) N

BD (1) C2–Br6

1.98481

0.7256 (sp2.50) C + 0.6881 (sp6.73) Br

BD (1) N3–C4

1.96673

0.7704 (sp2.16) N + 0.6376 (sp2.33) C

BD (1) C4–C5

1.98665

0.6985 (sp1.70) C + 0.7157 (sp1.35) C

BD (2) C4–C5

1.81687

0.6419 (p1.00) C + 0.7668 (p1.00) C

BD (1) C4–H7

1.97477

0.7885 (sp2.03) C + 0.6150 (sp0.00) H

BD (1) C5–N8

1.99141

0.6175(sp2.40) C + 0.7886 (sp1.81) N

BD (1) N8–O9

1.99488

0.7044 (sp2.10) N + 0.7098 (sp3.09) O

BD (2) N8–O9

1.98619

0.6303 (p1.00) N + 0.7763 (p1.00) O

BD (1) N8–O10

1.99620

0.7041 (sp2.13) N + 0.7101 (sp2.13) O

LP (1) S 1 LP (2) S1 LP (1) N3 LP (1) Br 6 LP (2) Br 6 LP (3) Br 6 LP (1) O9 LP (2) O9 LP (1) O10 LP (2) O 10 LP (3) O 10 BD (1) S1–C2

1.98106 1.58823 1.88328 1.99114 1.95703 1.90102 1.98155 1.88872 1.98131 1.89946 1.45304 0.08607

sp0.50 p1.00 P2.26 sp0.15 p1.00 p1.00 sp0.32 p1.00 p0.32 p1.00 p1.00 0.7298 (sp4.96) S  0.6837 (sp2.02) C

BD (1) S1–C5

0.03286

0.7296 (sp4.78) S  0.6838 (sp2.58) C

BD (1) C2–N3

0.03169

0.7732 (sp1.60) C  0.6342 (sp1.63) N

BD (2) C2–N3

0.40118

0.7423 (p1.00) C  0.6701 (p1.00) N

BD (1) C2–Br6

0.05777

0.6881 (sp2.50) C  0.7256 (sp6.73) Br

BD (1) N3–C4

0.01389

0.6376 (sp2.16) N  0.7704 (sp2.33) C

BD (1) C4–C5

0.02619

0.7157 (sp1.70) C  0.6985 (sp1.35) C

BD (2) C4–C5

0.30398

0.7668 (p1.00) C  0.6419 (p1.00) C

BD (1) C4–H7

0.01957

0.6150 (sp2.03) C  0.7885 (sp0.00) H

BD (1) C5–N8

0.09558

0.7886 (sp2.40) C  0.6175 (sp1.81) H

BD (1) N8–O9

0.05605

0.7098 (sp2.10) N  0.7044 (sp3.09) O

BD (2) N8–O9

0.64892

0.7763 (p1.00) N  0.6303 (p1.00) O

BD (1) N8–O10

0.05739

0.7101 (p2.13) N  0.7041 (sp3.13) O

NBO/NLMO analysis NBO (Natural Bond Orbital) analysis provide an efficient method for studying intra and inter molecular bonding and interaction among bonds, and also provides a convenient basis for investigation charge transfer or conjugative interactions in molecular system [37]. Another useful aspect of NBO method is that it gives information about interactions in both filled and virtual orbital

) S + 0.7296 (sp

)C

spaces that could enhance the analysis of intra and intermolecular interactions. The second order Fock matrix was carried out to evaluate the donor–acceptor interactions in the NBO analysis [38]. For each donor NBO (i) and acceptor NBO (j), the stabilization energy associated with i ? j delocalization can be estimated as,

Eð2Þ ¼ DEij ¼ qi

Fði; jÞ2 si sj

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402 Table 10 Significant NLMO’s occupancy, percentage from parent NBO and atomic hybrid contributions of 2-bromo-5-nitrothiazole calculated at B3LYP level using 6311++G(d,p) basis set. Bond

Occupancy

Percentage from parent NBO

Hybrid contributions Atom

Percentage

BD(2) C2–N3

2.00000

92.9864

BD(2) C4–C5

2.00000

90.8034

C2 N3 C4 C5 C2 N3 C4 C5 N8 O9 O10 S1 C2 N3 C4 C5 S1 C2 N3 C2 N3 Br6 C5 N8 O9 O10 C5 N8 O9 O10 N8 O9 O10

41.406 51.582 3.439 1.770 1.790 1.483 36.999 53.806 2.190 1.388 1.407 77.277 7.400 5.897 5.540 3.830 1.607 2.163 94.083 2.465 1.415 94.857 1.361 2.366 94.372 1.303 1.025 2.233 1.282 94.951 17.171 11.521 70.915

LP (2) S1

2.00000

77.2750

LP (1) N3

2.00000

94.077

LP (3) Br6

2.00000

94.8569

LP (2) O9

2.0000

94.3716

LP (2) O10

2.0000

94.9508

LP (3) O10

2.0000

70.9149

where qi is the donor orbital occupancy, ei, ej are diagonal elements (orbital energies) and F(i, j) is the off-diagonal NBO Fock matrix clement. In Table 8, the perturbation energies of significant donor–acceptor interactions are presented. The larger the E(2) value, the intensive is the interaction between electron donors and electron acceptors. In BNT, the interactions between the third lone pair of oxygen O10 and the antibonding of N8–O9 have the highest E(2) value around 163 kcal/mol. The other significant interactions giving stronger stabilization to the structure are the interactions between antibonding of C2–N3 and the antibonding of C4–C5 and the interactions between the second lone pair of sulfur S1 and the antibonding of C2–N3. Table 9 gives the occupancy of electrons and p-character [39] in significant NBO natural atomic hybrid orbitals. In C–H bonds, the hydrogen atoms have almost 0% of p character. On contrary, almost 100% p-character was observed in both the atoms of all the p bonding between C2–N3, C4–C5, N8–O9. Similarly, 100% p-character was observed in the second lone pairs of S1, Br6, O9, and O10 and in the third lone pair of Br6. The natural localized molecular orbital (NLMO) analysis has been carried out since they show how bonding in a molecule is composed from orbitals localized on different atoms. The derivation of NLMOs from NBOs gives direct insight into the nature of the localized molecular orbital’s ‘‘delocalization tails’’ [40,41]. Table 10 shows significant NLMO’s occupancy, percentage from parent NBO and atomic hybrid contributions of BNT calculated at B3LYP level using 6-311++G(d,p) basis set. The NLMO of third lone pair of oxygen atom O10 is the most delocalized NLMO and has only 71% contribution from the localized LP(3) O10 parent NBO,

401

and the delocalization tail (29%) consists of the hybrids of N8 and O9. Similarly, the second lone pair of sulfur atom S1 has delocalization tail (23%) consists of hybrids of C2, N3, C4 and C5. Among the bonded orbitals, NLMO due to BD(2) C4–C5 has 91% contribution from the parent NBO and the delocalization tail consists of the hybrids of C2, N3, N8, O9 and O10. These larger delocalization tails indicate that they are strongly delocalized into the regions of vicinal BD (2) N8–O9, BD (2) C4–C5, BD (1) N8–O9 and BD (2) C2–N3 antibonds. This delocalization can also be observed in the perturbation theory energy analysis given in Table 8. Conclusion In the present work, the fundamental modes of the compound 2-bromo-5-nitrothiazole have been investigated by FTIR and FTRaman spectroscopic techniques. The molecular structural parameters like bond length and bond angle, thermodynamic properties and vibrational frequencies of the fundamental modes of the optimized geometry have been determined from ab initio and DFT calculations using 6-311++G(d,p) basis set. The computed geometrical parameters are compared with the observed X-ray diffraction data of similar compound. The complete vibrational assignments of wave numbers are made on the basis of potential energy distribution (PED). Close agreement between the experimental and scaled frequencies were achieved. The frontier molecular orbitals have been visualized and the HOMO–LUMO energy gap has been calculated. The stability and intramolecular interactions have been interpreted by NBO/NLMO analysis and the transactions give stabilization to the structure have been identified by second order perturbation energy calculations. The calculation of first hyperpolarizability reveals that the title compound possesses good NLO properties. We believe that this study reveals the interesting spectroscopic and electronic properties of the title compound and which will be useful to those who are in the pursuit of experimental and theoretical details of the title molecule. Acknowledgements The authors are thankful to Manonmaniam Sundaranar University, Tirunelveli, India. References [1] H. Hof, O. Zak, E. Schweizer, A. Denzler, J. Antimicrob. Chemother. 14 (1) (1984) 31–39. [2] H. Hof, Zentralbl. Bakteriol. Mikrobiol. Hyg. B 181 (1–2) (1985) 64–70. [3] H. Hof, M. Rieffert, V. Sticht-Groh, O. Zak, E.H. Schweizer, Antimicrob. Agents. Chemother. 26 (4) (1984) 498–500. [4] H. Hof, K.M. Müller, W. Schrank, E.H. Schweizer, O. Zak, Arzneimittelforschung 37 (3) (1987) 306–309. [5] A.C. Cuckler, A.B. Kupferberg, N. Millman, Antibiot. Chemother. 5 (1955) 540– 550. [6] M.O. Kolosova, L.E. Chalaya, Z.K. Veronina, Med. Parazitol. Parazit. Bolezni 30 (1961) (1961) 703–709. [7] L. Shuttleworth, M.A Weaver, The Chemistry and Application of Dyes, in: D.R. Waring, G. Hallas (Eds.), Plenum Press, New York, 1990, p. 107. [8] M.A. Weaver, L. Shuttleworth, Dyes Pigm. 3 (1982) 133–160. [9] R. Egli, The Design and Synthesis of Organic Dyes and Pigments, in: A.T. Peters, H.S. Freeman (Eds.), Elsevier, London, 1991, p. 1. [10] V. Arjunan, S. Sakiladevi, T. Rani, C.V. Mythili, S. Mohan, Spectrochim. Acta A 88 (2012) 220–231. [11] H.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, H.Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, K. Toyota, R. Fukuda, J.Hasegawa, M. Ishida, R. Nakajima, Y. Honda, O. Kilao, H. Nakai, T. Verven, J. A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V.N. Staroveror, R. Kobayashi, J. Normand, K. Ragavachari, A. Rendell, J.C. Burant, S. J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Strattmann, O. Yazyev, A.J. Austin, R. Cammi, J.W. Ochetrski, R.L. Martin, K. Morokuma, V.G. Zakrazawski, G.A.Votn, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, Gaussian O.G., Revision A.O2, Gaussian Inc., Wallingford, CT, 2009. [12] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.

402 [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]

E. Gobinath, R.J. Xavier / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 394–402 C. Lee, W. Yang, R.G. Parr, Phys. Rev. B37 (1998) 785–789. T. Sundius, J. Mol. Struct. 218 (1990) 321–326. T. Sundius, Vib. Spectrosc. 29 (2002) 89–95. MOLVIB (V.7.0): Calculation of Harmonic Force Fields and Vibrational Modes of Molecules, QCPE Program No. 807, 2002. R.S. Tanke, B.M. Foxman, Acta Cryst. E63 (2007) o4718. J. Karpagam, N. Sundaraganessan, S. Sebastian, S. Manoharan, M. Kurt, J. Raman Spectrosc. 41 (2010) 53–62. T. Vijayakumar, H. Joe, C.P.R. Nair, V.S. Jayakumar, Chem. Phys. 343 (2008) 83. M. Arivazhagan, S. Jeyavijayan, Spectrochim. Acta, Part A 79 (2011) 376–383. D.A. Kleinman, Phys. Rev. 126 (1962) 1977–1979. H. Tanak, Y. Köysal, Sß. Isßık, H. Yaman, V. Ahsen, Bull. Korean. Chem. Soc. 32 (2) (2011) 673–680. M. Karaback, M. Cinar, M. Kurt, J. Mol. Struct. 885 (2008) 28–35. N. Sundaraganesan, S. Ilakiamani, H. Saleem, P.M. Wojieehowski, D. Michalska, Spectrochim. Acta, Part A 61 (2005) 2995–3001. D.N. Sathyanarayana, Vibrational Spectroscopy Theory and Application, second ed., New Age International (P) Limited Publishers, New Delhi, 2004. G. Socrates, Infrared and Raman Characteristic Group Frequencies, Tables and Charts, Third ed., Wiley, Chichester, 2001.

[27] R.J. Xavier, E. Gobinath, Spectrochim. Acta A 86 (2012) 242–251. [28] N.S. Chiu, J.D. Ewbank, M. Askari, L. Schafer, J. Mol. Struct. 54 (1979) 185–190. [29] H. Mollendal, S. Gundersen, M.A. Tafipolsky, H.V. Volden, J. Mol. Struct. 444 (1998) 47–52. [30] S. Samdal, T.G. Strand, M.A. Tafipolsky, L.V. Vilkov, M.V. Popik, H.V. Volden, J. Mol. Struct. 435 (1997) 89–95. [31] E.F. Mooney, Spectrochim. Acta 20 (6) (1964) 1021–1025. [32] J. Arthur, L. Plante, D.H. Stidham, Spectrochim. Acta A 74 (2009) 808–818. [33] M. Amalanathan, V.K. Rastogi, I.H. Joe, M.A. Palafox, R. Tomar, Spectrochim. Acta A78 (2011) 1437–1444. [34] K. Fukui, Science 218 (1982) 747–754. [35] L. Padmaja, C. Ravi Kumar, D. Sajan, I.H. Joe, V.S. Jayakumar, G.R. Pettit, J. Raman Spectrosc. 40 (2009) 419–428. [36] S. Sagdinc, H. Pir, Spectrochim. Acta A73 (2009) 181–187. [37] M. Snehalatha, C. Ravikumar, I.H. Joe, N. Sekar, V.S. Jayakumar, Spectrochim. Acta A 72 (2009) 654–662. [38] M. Szafram, A. Komasa, E.B. Adamska, J. Mol. Struct. 827 (2007) 101–107. [39] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899–926. [40] A.E. Reed, P.V.R. Schleye, Inorg. Chem. 27 (1988) 3969–3987. [41] R.J. Xavier, E. Gobinath, Spectrochim. Acta A 91 (2012) 248–255.