Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 237–251

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Molecular orbital studies (hardness, chemical potential and electrophilicity), vibrational investigation and theoretical NBO analysis of 4-40 -(1H-1,2,4-triazol-1-yl methylene) dibenzonitrile based on abinitio and DFT methods N.R. Sheela a,b,⇑, S. Muthu a, S. Sampathkrishnan a a b

Department of Applied Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602105, India Research and Development Centre, Bharathiar University, Coimbatore 641046, 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

 Vibrational spectra of 4-HTMDBN is

Molecular structure of 4-40 -(1H-1,2,4-triazol-1-yl methylene) dibenzonitrile (4-HTMDBN). A complete vibrational analysis is performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT) based on scaled quantum mechanical approach. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. NLO and NBO properties of 4-HTMDBN were performed by DFT with 6-31G(d,p) basis set. Electronic transition within the molecule and HOMO and LUMO energy 4-HTMDBN were studied. MEP sites give information about the region from where the compound can undergo non-covalent interaction. Thermodynamic properties of the title compound were calculated.

recorded and analyzed.  Vibrational assignments PED of 4-

HTMDBN were calculated.  The electron density and Fukui

functions are calculated.  The NLO and thermodynamic

properties are calculated theoretically.

a r t i c l e

i n f o

Article history: Received 3 May 2013 Received in revised form 1 July 2013 Accepted 2 October 2013 Available online 17 October 2013 Keywords: FT-IR FT-Raman DFT

a b s t r a c t The Fourier transform infrared (FTIR) and FT Raman (FTR) of 4-40 -(1H-1, 2, 4-triazol-1-yl methylene) dibenzonitrile (4-HTMDBN) have been recorded and analyzed. The equilibrium geometry harmonic vibrational frequencies have been investigated with the help of standard HF and DFT methods with 631G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Theoretical simulations of the FTIR and FTR spectra of the title compound have been calculated. The 1H and 13C Nuclear Magnetic Resonance (NMR) chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. The stability of the molecule has been analyzed using natural bond orbital (NBO) analysis. The linear polarizability (a) and the first order hyperpolarizability (b)

⇑ Corresponding author at: Department of Applied Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602105, India. Tel.: +91 9840861987. E-mail address: [email protected] (N.R. Sheela). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.007

238 Fukui function:NBO

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values of the investigated molecule have been computed using HF/DFT/6-31G(d,p) methods on the finite field approach. UV–Vis spectrum of the compound is recorded and the electronic properties such as HOMO and LUMO energies, are performed. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (v), electrophilicity index (x), hardness (g) and chemical potential (q) are all correlated with the HOMO and LUMO energies with their molecular properties. Mulliken population analysis on atomic charges, molecular electrostatic potential maps (MEP) and thermodynamical properties of title compound at different temperature have been calculated. Ó 2013 Elsevier B.V. All rights reserved.

Introduction The 4-40 (1H, 1,2,4-triazol-1-yl-methylene) dibenzonitrile (4-HTMDBN) is an aromatase inhibitor effectively used to treat breast cancer by decreasing estrogen levels in postmeno-pasual women. 4-HTMDBN has certain advantages over other current forms of treatment as it has been demonstrated to be superior in all stages of breast cancer treatment [1]. The use of letrozole has been known to induce ovulation in 75–80% women [2–4]. Jamal zidan et al. [5] reported that the compound under investigation has a safe effect on the plasma lipid and triglceride upase profiles of postmenopausal women with meta static blast cancer. Estradiol levels were maximally suppressed within 6 months of treatment. The increased levels of total Cholestrol during treatment were reversible and returned to normal levels after 3 months. In recent years the abinitio Hartree–Fock (HF) level and DFT has become a powerful tool in the investigation of molecular structure and vibrational spectra. DFT calculations of vibrational spectra of many organic system [6–8] have promising conformity with experimental results. The literature survey reveals DFT calculations and experimental studies have not been reported for the title compound (4-HTMDBN). The literature survey reveals HF and DFT calculations and experimental studies have not been reported for the title compound (4-HTMDBN). To fulfill the lacunae the current investigation related to molecular structure and FTIR, FTR spectral investigation of the compound 4-HTMDBN have been carried out and reported. Vibrational spectra of 4-HTMDBN have been analyzed on the basis of calculated potential energy distribution (PED). The redistribution of electron density (ED) in various bonding and antibonding orbitals along with E(2) energies have been calculated by natural bond orbital (NBO) using DFT method. Mean polarizability of (4-HTMDBN) have been investigated using DFT method. Based on ab initio HF and DFT calculations using 6-31G(d,p) basis set, highest occupied molecular orbital (HOMO)

Fig. 1. Numbering system adopted to the molecular structure of 4-HTMDBN.

energy and lowest unoccupied molecular orbital (LUMO) energy, and the thermodynamical properties such as zero-point vibrational energy (ZPVE), rotational constants, entropies and dipole moment were calculated. In addition, Nuclear magnetic resonance (NMR), UV–Visible spectral analysis, Molecular electrostatic potential (MEP) and Non linear optical properties for the title compound using the HF/6-31G(d,p) and DFT/B3LYP/6-31G(d,p) levels of theories were studied. Experimental details The compound 4-HTMDBN whose molecular structure with numbering system shown in Fig. 1, was procured from the Sigma–Aldrich chemical Company (USA), with stated purity of 98% and used as such without further purification. The FT-IR spectrum of the sample was recorded in the region 4000–400 cm1 in an evacuation mode using KBr pellet technique with 1.0 cm1 resolution on a PERKIN ELMER FT-IR spectrophotometer. The FT-Raman spectrum of the title compound was recorded using 1064 nm line of Nd–YAG laser as excitation wavelength in the region 4000– 100 cm1 on a Thermo electron Corporation Model Nexus 670 spectrophotometer equipped with FT-Raman module accessory. The observed experimental and simulated FT-IR and FT-Raman spectra using the HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods of calculation are shown in Figs. 2 and 3. The carbon NMR spectra 500 MHz was recorded at 301.2 k on BRUCKER AVANCE III NMR spectrometer, CDCl3 was used as a solvent and TMS as an internal standard. The proton spectra was recorded at 299.6 k on the same instrument using CHCl3 as a solvent. The measured 13C and 1H were shown in Figs. 4 and 5. The ultraviolet absorption spectra of 4-HTMDBN was examined in the range 250 nm using CARY 5E UV–Vis NIR spectrophotometer. The spectral measurements were carried out at Sophisticated Analytical Instruments Facility (SAIF), Indian Institute of Technology (IIT), Chennai, India.

Fig. 2. Theoretical and experimental FTIR Spectra of 4-HTMDBN.

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 237–251

Fig. 3. Theoretical and experimental FT Raman Spectra of 4-HTMDBN.

using Gaussian 03W [9] program package, invoking gradient geometry optimization [10]. To predict the optimized molecular structure and vibrational wavenumber, calculations are carried out using B3LYP method. The optimized geometry corresponding to the minima on the potential has been obtained by solving self-consisting field equation iteratively. The harmonic Vibrational frequencies were calculated at the same level of theory for the optimized structure. The incompleteness of the basis set and vibrational anharmonicity consequences the overestimation of the computational frequencies. Therefore scaling of the force field was performed according to the scaled quantum mechanical procedure (SQM) [11,12] and obtained frequencies were scaled by 0.8991 HF [13] and 0.9614 (B3LYP [14] to obtain a better agreement between the theory and the experiment. Normal co-ordinate analysis as suggested by Pulay et al. [12] have been written as input for the MOLVIB program. It should be noted that Gaussian 03W package does not calculate the Raman intensity. The recorded spectrum is in Raman intensity and computed is Raman activity. Since we are comparing experimental with theoretical spectra we are converting the Raman activity into relative Raman intensities. The Raman activities (Si) calculated by the Gaussian 03W program package [9] and adjusted during the scaling procedure with MOLVIB was converted to the relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [15,16]

Ii ¼

Fig. 4. C13 Spectrum of 4-HTMDBN (100.6 MHz).

239

f ðmo  mi Þ4 Si mi½1  expðhcmi =kTÞ

where mo is the exciting frequency (in cm1 units) mi is the vibration wavenumber of the ith normal mode; h, c and k are the universal constants and f is the suitably chosen common scaling factor for all the peak intensities. The natural bonding orbital (NBO) calculations [17] were performed using NBO 3.1 program as implemented in the Gaussian 03W package at the above said level in order to understand various second order interactions between the filled orbitals of one subsystem and vacant orbital of another subsystem which is a measure of the intermolecular and intramolecular delocalization or hyperjunction. The mean linear hyperpolarizability and mean first hyperpolarizability properties of the title compound were obtained based on theoretical calculations. Finally, the calculated normal mode vibrational frequencies also provide thermodynamical vibrational properties through the principle of statistical mechanics. In addition, the geometry of the title compound, together with that of DMSO is fully optimized. 13C and 1H NMR chemical shifts were calculated with GIAO approach [18,19] by applying DFT/631G(d,p) method. Results and discussions Geometrical structure

Fig. 5. 1H Spectrum of 4-HTMDBN (400.2 MHz).

Computational details The entire set of quantum chemical calculations were performed using the Hartree–Fock (HF) and density functional theory (DFT) calculations with B3LYP levels using 6-31G(d,p) as a basis set

The optimized structure parameters of 4-HTMDBN is calculated by DFT and HF level with 6-31G(d,p) basis set shown in Table 1 in accordance with the atom numbering scheme given in Fig. 1. Table 1 compares the calculated bond length and bond angles for 4-HTMDBN with the XRD data of structurally similar molecule, Baclofen Monohydrochloride [20]. General priorities for reproducing the experimental bond length and bond angles are not present among HF and DFT levels. However, all the bond lengths and bond angles computed with the DFT-B3LYP levels show excellent agreement with the experimental structural parameters. Some values deviates when comparing with the XRD data and these differences are probably due to intramolecular interactions in the solid state. Despite these differences, the calculated geometrical parameters

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Table 1 Optimized geometrical parameters for 4-HTMDBN computed at HF/B3LYP 6-31G(d,p).

a

Parameters bond length (Å)

HF/6-31G(d,p)

B3LYP/6-31G(d,p)

Experimentala

Parameters bond angle (°)

HF/6-31G(d,p)

B3LYP/6-31G(d,p)

Experimentala

C3–C4 C3–H23 C4–C5 C4–H24 C5–C6 C5–C9 C6–C7 C6–H25 C7–H26 C9–N10 C9–C15 C9–H27 N10–N11 N10–C14 N11–C12 C12–N13 C12–H28 N13–C14 C14–H29 C15–C16 C15–C20 C16–C17 C16–H30 C17–C18 C17–H31 C18–C19 C18–C21 C19–C20 C19–H32 C20–H33 C21–N22

1.38 1.074 1.391 1.076 1.388 1.527 1.384 1.074 1.074 1.455 1.525 1.082 1.344 1.334 1.294 1.352 1.07 1.298 1.069 1.392 1.386 1.379 1.076 1.392 1.074 1.386 1.445 1.385 1.074 1.073 1.136

1.393 1.085 1.398 1.084 1.402 1.527 1.389 1.087 1.085 1.467 1.529 1.095 1.361 1.357 1.325 1.363 1.081 1.322 1.08 1.402 1.4 1.39 1.086 1.405 1.084 1.403 1.434 1.392 1.084 1.085 1.163

1.42 1.1 1.42 1.1 1.42 1.497 1.42 1.1 1.1 1.47 1.497 1.113 1.426 1.362 1.26 1.346 1.1 1.26 1.1 1.42 1.42 1.42 1.1 1.42 1.1 1.42 1.469 1.42 1.1 1.1 1.158

C2–C3–C4 C2–C3–H23 C2–C7–C6 C2–C7–H26 C4–C3–H23 C3–C4–C5 C3–C4–H24 C5–C4–H24 C4–C5–C6 C4–C5–C9 C6–C5–C9 C5–C6–C7 C5–C6–H25 C5–C9–N10 C5–C9–C15 C5–C9–H27 C7–C6–H25 C6–C7–H26 N10–C9–C15 N10–C9–H27 C9–N10–N11 C9–C10–C14 C15–C9–H27 C9–C15–C16 C9–C15–C20 N11–N10–C14 N10–N11–C12 N10–C14–N13 N10–C14–H29 N11–C12–N13 N11–C12–H28 N13–C12–H28 C12–N13–C14 N13–C14–H29 C16–C15–C20 C15–C16–C17 C15–C16–H30 C15–C20–C19 C15–C20–H33 C17–C16–H30 C16–C17–C18 C16–C17–H31 C18–C17–H31 C17–C18–C19 C17–C18–C21 C19–C18–C21 C18–C19–C20 C18–C19–H32 C18–C21–N22 C20–C19–H32 C19–C20–H33

119.6 120 119.8 119.9 120.5 120.8 119.4 119.8 119.1 118.6 122.3 120.5 120.3 110.4 113.9 107.7 119.2 120.3 112.6 104.7 119.3 131.7 107.1 118.1 122.7 108.9 103 110.7 123.4 114.8 122.1 123.1 102.6 126 119.2 120.8 119.9 120.4 120.5 119.3 119.6 120.4 119.9 120 119.9 120.1 120 119.9 179.8 120.1 119.1

120.1 119.7 119.8 119.7 120.3 120.6 119.2 120.2 119.1 122.5 118.4 120.9 119.8 112.5 113.9 107.4 119.4 120.5 110.2 104.4 119.3 131.1 107.8 118.9 122 109.5 102.2 110.4 123.2 115.4 121.5 123.1 102.5 126.4 119.1 120.9 119.6 120.6 119.9 119.5 119.7 120.6 119.7 119.8 120.1 120.1 119.9 119.7 180 120.4 119.5

120.00 120.00 120.00 120.00 120.00 120.00 120.00 121.40 118.60 121.00 119.00 120.00 120.00 113.00 113.00 110.30 119.51 119.39 110.30 104.50 119.81 130.50 107.50 118.00 122.00 110.78 102.61 111.61 121.22 114.00 124.50 124.50 102.00 125.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 120.00 180.00 120.00 120.00

Taken from the Ref. [20].

represent a good approximation, and they are the basis for the calculation of other parameters such as polarizability, vibrational frequencies and thermodynamic properties. Vibrational band assignments According to the theoretical calculation, 4-HTMDBN has a structure of C1 point group symmetry. The molecule has 33 atoms and 93 modes of fundamental vibrations which are active in both IR absorption and Raman scattering. Detailed description of vibrational modes can be given by means of normal coordinate analysis (NCA). For this purpose the full set of 136 standard internal valence coordinates are defined as shown in Table S1 (Supplementary material). From these a non-redundant set of local symmetry coordinates are constructed much like the internal coordinates rcommended by Fogarsi and Pulay [21,22] and is presented in Table S2 (Supplementary material). The vibrational analysis

obtained for the title molecule with the unscaled force field is usually greater than the experimental values due to neglect of anharmonocity in real system. The discrepancies between these two can be corrected either by computing anharmonic corrections explicitly or by introducing a scale field or by direct scaling of wavenumber with proper factor [23,24]. The detailed vibrational assignments of fundamental modes of 4-HTMDBN along with calculated IR and Raman intensities at HF and B3LYP levels using 6-31G(d,p) and normal mode descriptions (characterized by PED) are reported in Table 2. Some bands found in the predicted FT-IR and FT-Raman spectra were not observed in the experimental spectra of 4-HTMDBN. Therefore, a linearity between the experimental and scaled calculated wavenumber for HF/DFT method of 4HTMDBN can be estimated by plotting the calculated versus experimental wavenumbers as shown in Fig. 6. The correlation coefficient R2 for experimental and observed wavenumber computed from the DFT and HF methods were found to be

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N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 237–251 Table 2 Detailed assignments of fundamental vibrations of 4-HTMDBN by normal mode analysis based on SQM force field calculation using HF/B3LYP/6-31G(d,p). Mode No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

Experimental wave number (cm1)

HF/6-31G(d,p)

FTIR

FT Raman

Theoretical wave number (cm1) scaled

IIRa

IRamanb

Theoretical wave number (cm1) scaled

IIRa

IRamanb

3150 (m) 3120 (m)

– – 3095 (m) 3090 (w) 3085 (w) 3080 (w) – – – 3054 (w) 2987 (vs) 2270 (m) 2255 (m) – – 1560 (m) 1552 (m) – 1493 (s) 1464 (w) 1420 (w) – 1375 (m) – 1338 (m) 1310 (w) – 1290 (w) 1280 (w) 1265 (w) – – 1190 (s) 1180 (m) 1175 (m) 1170 (w) 1165 (w) 1161 (w) – 1128 (w) 1100 (w) 1097 (w) – – – – 952 (w) 945 (w) 940 (w) 935 (w) – 861 (w) 850 (w) 847 (w) 830 (w) 825 (w) 820 (w) – 780 (w) – 740 (w) 711 (w) 690 (w) – – 636 (w) 625 (w) – – –

3106 3094 3051 3047 3042 3040 3034 3032 3018 3012 2931 2346 2344 1636 1634 1586 1582 1576 1514 1513 1458 1413 1405 1399 1353 1327 1306 1301 1290 1216 1210 1201 1184 1182 1174 1167 1166 1144 1133 1130 1077 1073 1006 1005 1004 1003 998 992 987 958 945 924 884 874 863 857 847 820 796 752 738 715 700 677 644 636 631 575 569 553

0.5 9.3 2.9 1.7 3.5 4.0 2.3 3.1 4.7 8.5 4.4 41.2 57.2 2.5 16.7 1.5 3.0 100.3 28.1 10.7 27.1 23.2 27.6 21.2 21.9 4.3 8.0 67.3 24.1 38.8 15.7 10.5 2.9 1.6 2.8 0.7 3.8 5.0 2.9 39.6 0.4 1.0 28.3 12.0 2.1 14.8 0.1 4.7 0.4 9.0 1.3 6.3 10.1 18.3 0.4 0.1 20.2 51.6 33.3 2.6 4.7 4.2 6.8 22.0 17.2 0.7 3.5 19.8 21.7 1.3

12.6 29.0 22.4 27.1 23.3 21.9 13.2 11.3 11.3 11.1 12.6 100.1 91.9 51.8 30.3 0.2 0.2 0.8 1.2 1.3 1.3 0.1 0.7 4.2 1.5 0.3 0.5 3.4 2.1 1.1 1.3 1.4 2.5 1.8 0.8 5.3 19.3 2.3 7.2 1.6 0.1 0.3 0.8 0.2 0.1 0.3 0.0 0.4 0.6 0.9 0.3 0.1 0.3 1.5 0.6 0.4 1.6 5.7 2.2 3.0 0.4 0.4 0.2 0.2 0.1 1.3 0.5 1.0 0.5 2.1

3157 3144 3099 3098 3096 3094 3086 3084 3070 3064 2989 2261 2260 1603 1599 1554 1550 1494 1490 1489 1413 1397 1391 1346 1322 1307 1288 1286 1280 1270 1248 1188 1186 1184 1172 1171 1165 1160 1147 1124 1104 1099 999 998 991 949 945 942 940 936 870 861 849 837 828 824 821 806 779 747 737 705 691 667 639 632 626 560 556 538

0.56 8.39 2.57 1.08 4.33 4.81 2.09 2.66 5.93 10.33 6.03 35.43 53.11 7.43 23.12 4.37 1.99 100.87 16.67 22.80 14.48 19.46 28.98 22.67 20.42 6.34 2.47 1.66 7.72 85.09 30.15 41.92 4.89 9.18 8.57 5.34 2.69 2.30 0.35 42.00 8.84 3.17 13.45 7.24 60.78 0.25 0.50 0.24 0.10 18.53 8.59 15.19 15.66 16.20 2.37 6.76 8.45 65.26 60.38 9.81 9.49 4.56 6.11 29.18 12.64 0.64 4.44 23.90 26.24 1.11

8.92 24.14 21.27 20.71 13.95 14.33 7.17 8.03 8.47 8.04 12.09 100.00 88.70 49.77 27.29 0.18 0.21 0.25 0.92 0.73 1.32 0.08 0.27 2.34 0.70 0.37 0.43 0.44 0.77 2.17 1.98 0.91 5.05 6.66 0.91 1.28 7.12 4.73 17.44 1.13 0.05 0.11 0.02 0.01 1.42 0.12 0.19 0.17 0.20 0.49 0.36 0.59 1.48 0.54 0.79 0.27 0.29 3.18 1.14 1.89 0.27 0.10 0.25 0.13 0.07 1.04 0.38 0.24 0.13 0.83

3074 3061 – 2990 2300 2231 1680 1607

(w) (w) (m) (s) (w) (m) (vs)

1503 (vs)

1434 1408 1385 1340 – – 1298

(vs) (w) (w) (vs)

(m)

1270 (m) 1240 (vs) 1199 (vs)

1138 (s)

1003 (vs) 990 (m) 982 (m) 954 (s)

867 (s) 858 (m)

789 (m) 774 (m) 760 (vs)

677 (s) 657 (s)

567 (s) 555 (s) 548 (m)

B3LYP/6-31G(d,p)

Vibrational assignment (%PED)

m C–H (98) m C–H (96) m C–H (97) m C–H (95) m C–H (96) m C–H (97) m C–H (95) m C–H (96) m C–H (95) m C–H (96) m C–H (96) m C„N (86) m C„N (85) m C–C (85) m C–C (84) m C–C (82) m C–C (27), b C–H (36) m C–C (57), b C–H (35) m C–C (35), b C–H (39), c H–C–N (20) m C–C (37), b C–H (34) m C–C (32), b C–H (31) m C–C (41), b C–H (33) m C–C (39), b C–H (34) m C–C (26), m C–N (17), b C–H (31) c HCCC (28), c HCN (15), tR1sym (14), b CCH (13) c HCN (38), c HCCC (28), b CCH (13) c HCCC (26), b CCH (17), m C-C (15), b C-H (35) m C–C (16), b C–N–C (19), b C–H (33), m C–N (31), m C–C (21), b C–N–C (15), b C–H (36) m C–C (54), b C–N–C (17) b N–C–C (11), b C–H (31) c HCCC (17), b CCCH (13), m C–N (12) b C–C–N (11), tR1sym (15), tR2sym (12) b C–C–C (17), m C–H (34) b C–C–H (24), b C–C–C (16) b C–C–H (35), m C–C (12), b C–N (11) b R1trig (19), b C–C–H (32) t b R2trig (22), b C–H (32) m C–C (10), b C–N (24), b C–C–H (16) m C–N (44), b C–N–C (13), m C–C (11), b R1sym (11) b R1sym (15), m C–C (13), c HCN (10), b C–H (34) c CCCN (29), m C–C (17), b C–H (30) c CCCN (16), m C–C (26), b C–H (31) tR1trig (17), tR2trig (15), b C–H (32) tR2trig (19), c C–H (21) tR2trig (47), c C–C (21), b NCC (16) tR1sym (16), b NCC (11) b CNC (47), c HCN (12), c C–H (11) tC–C (17), tR2trig (15), c C–H (27) tR1asym (38), tR1sym (24), m C–N (11) b CNC (47), c HCN (12) m C–N (22), tR1trig (19), c C–C–C–N (11) c C–C–C–N (17), b N–C–H (22), c C–H (11) c C–H (62), tR2sym (17), tR1sym (13) c C–H (27), m C–C (18), tR1sym (12), b C–C (10) c C–H (26), tR1trig (26),tR2trig (12) c C–H (26), bR1sym (17), bR1asym (11) c C–H (63), b R2asym (11) b R2sym (21), b R2asym (17), c C–H (33) tR1trig (35), tR2trig (25), c C–H (24) m C–C (12), b R1asym(17), c C–H (21) b C–C–C (44), b C–C–H (18) t C–C–C–H (17), tC–C–C–C (33) t R2trig (25), b C–C (32) tR1trig (16), b R1 asym (12), b C–C(32) tR1trig (16), tR2trig (25), t C–C(31) tR2asym (45), tR2sym (23), t C–C(21) b R1sym (22), b R1asym (12), b C–C(31) b N–C–C (38), b R1asym (18), b C–C (10) c C–C (60), tC-N(10) c C–C–C–N (11), tR1sym (12),tR1asym (22) (continued on next page)

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Table 2 (continued) Mode No.

71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93

Experimental wave number (cm1)

HF/6-31G(d,p)

FTIR

FT Raman

Theoretical wave number (cm1) scaled

IIRa

IRamanb

Theoretical wave number (cm1) scaled

IIRa

IRamanb

530 515 474 442 430 396 385 320 300 260 255 245 238 150 141 120 109 – – – – – –

552 512 488 458 432 407 404 323 302 262 252 247 237 153 145 119 110 62 59 50 37 30 26

0.3 1.8 5.7 1.3 0.6 0.1 0.3 0.2 0.4 2.4 2.6 0.3 1.1 7.8 7.1 1.0 1.1 3.4 0.7 3.6 1.2 0.8 0.4

0.9 1.0 1.3 1.7 0.4 0.0 0.0 0.3 0.3 0.3 0.4 0.4 0.9 0.3 0.5 0.1 0.2 0.5 1.5 0.5 2.3 0.8 1.2

537 512 483 450 422 398 395 319 300 256 248 243 235 148 140 115 107 60 52 48 35 30 25

0.09 2.29 10.03 0.56 0.47 0.28 0.60 0.19 0.98 3.96 3.47 1.56 1.46 10.25 9.98 1.22 1.79 4.58 1.49 5.68 2.02 1.06 0.38

0.39 0.64 0.78 1.20 0.24 0.01 0.01 0.17 0.24 0.21 0.42 0.18 0.50 0.25 0.43 0.11 0.14 0.49 0.85 0.63 1.97 0.59 0.91

(w) (m) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w) (w)

B3LYP/6-31G(d,p)

Vibrational assignment (%PED)

tC–C(48), b C–N–C (19), c C–C(24) b C–C–C (55), cC–C–C–N (12),tR2sym (11) t C–C (30), b R1sym (19), tC–N(12) c C–C–N (29), cC–N–C (21), tC–C (17) t C–C (24), b R1sym (19) t C–C (24), b R1sym (19),t C–N (12) b R2 asym (73), b R1sym (10) m H–C–C–C (11), b R1sym (17), tR1trig (12) c C–N–C (27), c H–C–C–C (11), b R1sym (12), tR2trig (11) tR1asy(14), c H–C–C–C (17), b R1tri (11) t R1sym (10), c C–N–C–C (15), b N–C–H(21) t R2sym (11), c C–N–C–C (15), b N–C–H(17) t R1sym (18), tR2asym (12), butt (18), b C–C–C (11) tR1sym (32), tR2trig (28), t R2asym(23) c C–N (15),tR2sym (10), tR1sym (25) t R1asym (27), tR2sym (17), b C–C–C (11) t R2asym (40), tR1sym (12), b C–C–C (11) t C–N (38),tR2asym (19), c H–C–N(12), cC–C–C(15) tR2asym(19). tR1asym (34), cH–C–N(11) tR2asym (41), cH–C–N(11) t C–N(42), t R2sym (31), tC–N(11) tR1asym (17), tR1sym (11) tC–N(19)

Notes: w, weak; vw, very weak; m, medium; s, strong; vs very strong; m, stretching; mas, asymmetric stretching; ms, symmetric stretching; asym, asymmetric; sym, symmetric; R1, Ring1; R2, Ring2; t, twisting; b, in plane bending; c, out of plane bending, butt, butterfly. a Relative absorption intensities normalized with highest peak absorption equal to 100. b Relative Raman intensities normalized to 100.

0.9769 and 0.9582, respectively. It can be noted from the R2 values that the theoretical prediction is in good agreement with the experimental wavenumbers. Also Fig. 6 reveals the overestimation of the calculated vibrational modes due to neglect of anharmonicity in real system. Inclusion of electron correlation in DFT to a certain extent makes the frequency values smaller in comparison with the HF frequency data. Plots of simulated IR and Raman spectra, pure Lorentzian band shapes were used with a bandwidth of 40 cm1. We have assigned the fundamental modes of 4-HTMDBN on the basis of a group vibrational concept and calculated vibrational wavenumbers, on the whole the predicted vibrational wavenumber are in agreement with the experimental results. C–H vibrations The heteroaromatic structure shows the presence of C–H stretching vibrations in the region 3100–3000 cm1, which is the characteristic of C–H stretching vibrations [25,26]. In our present study, the band observed at 3095, 3090, 3085, 3054, 2987 cm1 in the FT-Raman and a weak and medium strong bands observed at 3150, 3120, 3074, 3061 and 2990 cm1 in the FT-IR spectra are assigned to C–H stretching vibrations. The C–H stretching modes which are not observed experimentally have been predicted on the basis of PED percentage. The calculated modes by B3LYP method at 3157, 3144, 3099, 3098, 3096, 3094, 3086, 3084, 3070, 3064 and 2989 cm1 (mode Nos. 1–11) are pure modes, as it is evident from PED column, and they are almost contributing to more than 95%. The calculated values are in good agreement with the experimental data. The C–H in-plane bending vibrations appear in the frequency region 1000–1550 cm1 [27–29]. Normally the bands are very weak. In our present study the bands observed in the FT-IR spectrum at 1503, 1434, 1408, 1385, 1340, 1298, 1270, 1240, 1199 and 1003 cm1 are assigned to C–H in-plane bending vibration and their counter parts in the FT-Raman spectrum are observed

at 1552, 1493, 1464, 1420, 1375, 1338, 1310, 1290, 1280, 1265, 1190, 1180, 1175, 1170, 1165, 1161, 1128, 1100 and 1097 cm1. The theoretically calculated values 1550–999 cm1 (mode Nos. 17–43) are in good agreement with the experimental values. The C–H in-plane bending vibration is a highly mixed mode. The PED corresponding to this vibration is mixed with C–C stretching with contribution of 30%. The C–H out-of-plane bending vibration is expected in the range 750–1000 cm1 in the FT-IR spectra of substituted benzene [30,31]. The position of C–H out-of-plane vibration is determined almost extensively by the relative position of the substituents and is independent of nature [32]. KrishnaKumar et al. [33] have been assigned the C–H out of plane bending vibration in the region 986–825 cm1 in the FT-IR spectrum for 4-bromobenzonitrile. The bands observed at 990, 982, 954, 867, 858, 789, 774 and 760 cm1 in the FT-IR and 952, 945, 940, 935, 861, 850, 847, 830, 825, 820 and 780 cm1 in the FT-Raman spectra are assigned to C–H out -of-plane bending vibration and are presented in the Table 2. Cyanogroup vibration The characteristic wavenumber of C„N stretching vibration of benzonitrile falls in the region 2220–2240 cm1 [34] spectral range and it appears with strong Raman intensity whereas its IR intensity varies from medium strong to strong depending upon substituents(s). In 4-HTMPN, successive substitution of electron withdrawing or donating groups can also shift the C„N stretching frequency beyond the characteristics. The Raman intensity of C„N band is enhanced by the conjugation of the aromatic ring stretching and deformation modes often exhibit stronger Raman intensities than the C–N stretching vibration. A strong IR band at 2252 cm1 in 2-fluoro-5-methylbenzonitrile was assigned to C„N stretching vibration [35]. In the present case, characteristic C„N stretching wavenumber is observed in FT-IR spectrum as a very strong band at 2300 cm1 and 2231 cm1 and also very strong band in

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FT-Raman at 2270 and 2255 cm1 shows good correlation with theoretically predicted wavenumber at 2261 and 2260 cm1 (mode Nos. 12 and 13) with PED contribution of 86%. In benzoxazole, the C–N stretching vibration [36] have been reported a value of 1332 cm1 (FT-IR), 1315 (FT-Raman) and 1315 cm1 (HF). For 2mercaptobenzoxazole the C–N stretching mode was not reported in the FT-IR spectrum and the calculated value was 1495 cm1. For 2-mercaptobenzothiazole the C–N stretching mode was observed at 1332 cm1 in the FT-IR spectrum and at 1306 cm1 theoretically. In accordance with above conclusion, for our title molecule the C–N stretching vibrations are observed at 1340 and 1290 cm1 (mode Nos. 24 and 28) as a strong band in FT-IR and FT-Raman spectra respectively. The theoretically predicted value by B3LYP method at 1346 and 1286 cm1 exactly correlates with measured experimental data. The PED of these vibrations are mixed mode as it is evident from PED Table 2. Aromatic nitriles have two bands, one bands is of strong intensity in the region 580–540 cm1 and other of medium intensity in the region 430–380 cm1. The former band is due to the combination of the out-of-plane aromatic ring deformation vibration and the in-plane-deformation vibration of the –C–C„N group. The later band is due to the in-plane bending of the aromatic bond [37]. Based on the above literature data, we assign the C–C–N in plane bending vibrations as a medium band in FT-IR at 555 cm1 and is in good agreement with the theoretically computed wavenumber computed by B3LYP method at 556 cm1 (mode No. 69). The computed C–C–N out-of-plane bending vibration by B3LYP/6-31G(d,p) method at 450 cm1 (mode No. 20) with PED contribution of 29%. The other theoretically calculated CNC vibrations such as in-plane-bending and out-of-plane bending vibrations of CNC presented in Table 2, based on the literature data are in agreement with experimental observations.

C–C vibrations The ring carbon–carbon stretching vibrations occur in the region 1625–1430 cm1 [38]. In general, the bands are of variable intensity and are observed at 1625–1590, 1590–1575, 1540– 1470, 1465–1430 and 1380–1280 cm1 from the frequency ranges given by Varsanyi [39] for the five bands in the region. In the present study the frequency bands at 1680, 1607, 1503, 1434, 1408, 1385, 1340, 1298, 1270 and 1138 cm1 in FT-IR spectrum and 1560, 1552, 1493, 1464, 1420, 1375, 1290, 1280, 1265, 1175, 1161, 1128, 1100 and 1097 cm1 in FT-Raman are assigned to C–C stretching vibrations for 4-HTMDBN molecule, the theoretically computed wavenumber also present consistent agreement with experimental observation at 1603, 1599, 1554, 1550, 1494, 1490, 1489, 1413, 1397, 1391, 1346, 1288, 1286, 1280, 1270, 1172, 1160, 1147, 1124, 1104 and 1099 cm1 (mode Nos. 14–24, 27–30, 32, 35 and 38–42). The PED lies between 30% and 80% as shown in Table 2 with combination of C–H in plane bending in this region. In general, the C–C in-plane bending vibrations are at higher wavenumber than the C–C out-of-plane bending vibrations. In the present study, the calculated values 691 and 667 cm1 (mode Nos. 63 and 64) are assigned to C–C in-plane bending vibrations which are in good agreement with the observed band at 677 cm1 in FT-IR spectrum and the counterpart vibration in the FT-Raman spectrum is not observed. The C–C out of plane bending vibrations [40] are observed at 555 cm1 in FT-IR and at 530 cm1 in FT-Raman spectra (mode Nos. 69 and 71). The PED contribution for this mode is a mixed mode as it is evident from the Table 2. The remaining vibrations like CCC in-plane and out-of-plane bending vibrations are assigned with reference to the literature data and are presented in the Table 2.

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NMR spectral analysis The molecular structure of 4-HTMDBN is optimized by using B3LYP method with 6-31G(d,p) basis set. The experimental 13C and 1H spectra are presented in Figs. 4 and 5 respectively. 1H NMR spectrum provides information about the no of different types of protons and also the nature of immediate environment to each of them, whereas 13C NMR spectrum provides the structural information with regard to different carbon atoms present in the molecules. Then, gauge-including atomic orbital (GIAO) 13C and 1H chemical shift calculations of the title compound are calculated and compared with experimental values [41]. The GIAO method is one of the most common approaches for calculating nuclear magnetic shielding tensors. The results in Table 3 show that the range 13C NMR chemical shift of typical organic molecule is usually >100 ppm [42–44]; the accuracy ensures reliable interpretation of spectroscopic parameters. It is true from the above literature value, in our present studies, the title molecule also falls with the above literature data. In the 1H NMR spectrum, a singlet at 6.81 d indicates the methane proton. The above said, methane proton is calculated as 5.98 d for B3LYP. The peaks corresponding to aromatic ortho protons which are merged with CHCl3 peak are appeared as quadrate in the range 7.28–7.30 d and are found to be in the range of 6.73– 6.98 d for B3LYP. The meta protons of aromatic ring are responsible for the appearance of quadrate in the range 7.70–7.72 d and calculated as 6.81–6.95 d for B3LYP. In 13C NMR spectrum, the ipso carbons (C5, C15) of the benzene ring give signal at 141.76 d, and calculated value by B3LYP method appeared around 137 d. The meta carbons (C3, C7, C17 and C19) of benzene ring are responsible for the signal at 132.91 d, and are in good agreement with the calculated values. The signal due to alkyl methine carbon (C2) appears at 66.36 d, calculated as 61.42 d for B3LYP. The signal appeared at 117.82 d is due to C1 and C21 carbons of benzene ring are in good agreement with the calculated data. The signal appeared at 153.05 d and 143.68 d is due to C12 and C14 carbons of triazole ring and calculated as 147.42 and 139.65 d respectively for B3LYP. The above said relevant calculated 13C chemical shifts are listed in the Table 3. As it is seen from the Table 3, experimental 1H and 13C chemical shift values of the title compound are generally in agreement with the calculated 1H and 13 C chemical shifts data. NBO analysis Weak occupancies of the valence antibonds signal irreducible departures from an idealized localized Lewis structure which means true ‘‘delocalization effects’’ [45]. NBO analysis provides the most accurate possible natural Lewis structure picture of U, because all the orbital details are mathematically chosen to include the highest possible percentage of the electron density. A useful aspect of the NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra-and-inter-molecular interactions. The second order Fock matrix was carried out to evaluate the donor–acceptor interactions in NBO analysis [46]. The interactions result is the loss of occupancy from the localized NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilisation energy E(2) associated with the delocalization i ? j is estimated as, 2

E2 ¼ DEij ¼ qi

Fði; jÞ ej  ei

!

where qi is the donor orbital occupancy, ej and ei are diagonal elements and F(i,j) is the off diagonal NBO Fock matrix element.

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C7, C5–C6, C5–C9) leading to average stabilization of 4.35 kcal/mol. This enhanced further conjugate with antibonding orbital of p* (C2–C3, C4–C5) which leads to strong delocalization with an average stabilization energy 22.95 kJ/mol. The most important interaction energy, related to the resonance in the molecule, is due to interaction between lone pair N8 with antibonding r*(C1–C2) results in a stabilization energy of 14.31 kcal/mol that denotes larger delocalization while nitrogen N22 lead to stabilization energy of 14.29 kcal/mol to r*(C18–C21). This shows that the lone pair orbital participates in electron donation in the compound. The calculated values of E(2) are shown in Table 4. The interesting intramolecular hyperconjugative interaction of r electrons from C14–H29 to the r* antibonding orbital of C14–H29 leading to the stabilization energy of 39.87 kcal/mol. This enhanced to r(C14–H29) NBO further conjugates with r*(C20–H33), resulting in an enormous stabilization energy of 305.12 kcal/mol. Similarly another intramolecular hyperconjugative interaction of the r electrons from C20–H33 to the r* antibonding orbital of C20–H33 leading to the stabilization energy of 22.59 kcal/mol. This enhanced to r(C20–H33) NBO further conjugates with r*(C14–H29), resulting in an enormous stabilization energy of 209.15 kcal/mol as shown in Table 4. This highest interaction around the ring can induce large bioactivity in the molecule. Hyper polarizability calculations

Fig. 6. Correlation coefficient between observed and calculated frequencies.

Natural bond orbital analysis provides an efficient method for studying intra and inter molecular bonding and interaction among bonds, and also provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital acceptor orbital and the interacting stabilization energy resulted from the second-order-micro-disturbance theory are reported [47,48]. The larger the E(2) value, the more intensive is the interaction between donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system. Delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO orbitals and formally unoccupied (antibond or Rydberg) non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor interaction. NBO analysis has been performed on the 4-HTMDBN molecule at the DFT/ B3LYP/6-31G(d,p) level in order to elucidate the intramolecular, rehybridization and delocalization of electron density within the molecule. It is evident from the Table 6 the strong intramolecular hyperconjugative interaction of the r and p electrons of C–C to the anti C–C bond of the ring leads to stabilization of some part of the ring. These interactions are observed as increase in electron density (ED) in C–C anti-bonding orbital that weakens the respective bonds [49]. The electron density of six conjugated single bond of aromation (1.9 e) clearly demonstrates strong delocalization. Moreover there is no difference in charge distribution observed on all other carbon atoms. For example the intramolecular hyper conjugative interaction of r (C6–C7) distribute to r* (C1–C2, C2–

Analysis of organic molecules having conjugated p-electron systems and large hyperpolarizability using infrared and Raman spectroscopy has been evolved as a subject of research [50]. The first order hyperpolarizability (btotal) of 4-HTMDBN along with related properties (l, and Da) are calculated using HF and DFT B3LYP methods and 6-31G(d,p) basis set, based on the finite field approach. The polarizabilities and hyperpolarizabilities characterize the response of a system in an applied electric field [51,52]. In the presence of an applied electric field, the energy of a system is a function of the electric field, First order hyper-polarizability is a third rank tensor that can be described by a 3  3  3 array. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [53]. It can be given in the lower tetrahedral format. The components of btotal 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 homogeneous, this expansion becomes.

E ¼ Eo  la Fa  1=2aab Fa Fb  1=6babc Fa Fb Fc . . . where Eo is the energy of unperturbed molecule, Fa the field at the origin, la, aab and babc are the components of dipole moment, polarizability and the first order hyperpolarizability, respectively. The total static dipole moment l, the mean dipole polarizability (a), the anisotropy of the polarizability Da and the total first order hyperpolarizability btotal, using x, y, z components they are defined as 1=2

l ¼ ðl2x þ l2y þ l2z Þ < a >¼

axx þ ayy þ azz 3

Da ¼ 21=2 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xx  1=2

btotal ¼ ðb2x þ b2y þ b2z Þ

bx ¼ bxxx þ byyy þ bzzz by ¼ byyy þ bxxy þ byzz ;

and;

1=2

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 237–251 Table 3 Experimental and theoretical chemical shifts of 4-HTMDBN in (ppm).

13

C, 1H NMR spectra d

Atom position

Expt

B3LYP/6-31G(d,p)

C1 C2 C3 C4 C5 C6 C7 C12 C14 C15 C16 C17 C19 C20 C21 H23 H24 H25 H26 H27 H28 H29 H30 H31 H32 H33

117.82 66.36 132.91 128.9 141.76 128.9 132.91 153.05 143.68 141.76 128.9 132.91 132.91 128.9 117.82 7.28 7.70 7.70 7.28 6.81 8.07 8.09 7.72 7.30 7.30 7.72

109.25 61.42 123.54 121.6 137.55 125.12 128.22 147.42 139.65 136.91 121.5 129.52 127.4 120.25 110.58 6.84 6.98 6.81 6.73 5.98 7.55 7.45 6.85 6.98 6.77 6.85

bz ¼ bzzz þ bxxz þ byyz The HF/6-31G(d,p) results of electronic dipole moment li (i = x, y, z), polarizability aij and first order hyperpolarizability bijk are listed in Table S3 (Supplementary material). The calculated dipole moment and hyperpolarizability values obtained from HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods are collected in Table S3 (Supplementary material). The total molecular dipole moment of 4-HTMDBN from HF and B3LYP with 6-31G(d,p) basis set are 4.111D and 4.211D respectively, which are about four times greater than the value of urea (For urea l = 1.3732D). As urea is one of the prototypical molecules used in the study of the NLO properties of the molecular systems. Therefore it was used frequently as a threshold value for comparitive purposes. Similarly the first order hyperpolarizability of 4-HTMDPN with B3LYP/631G(d,p) basis set is 2.3800  1030 three and half times greater than the value of urea (bo = 0.372  1030 esu). Since the values of the first hyperpolarizability tensors of the o/p file of Gaussian 03W are reported in atomic units (a.u), the calculated values were converted into electrostatic units (1 a.u = 8.6393  1033 esu). From the computation the high values of the hyperpolarizability of 4-HTMDBN are probably attributed to the charge transfer existing between the phenyl rings within the molecular skeleton. This is evidence for non-linear optical (NLO) property of the molecule. 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 [54–7]. We conclude that the title compound is an attractive object for future studies of non-linear optical properties. Atomic net charges The calculation of effective atomic charges plays an important role in the application of quantum mechanical calculation to molecular systems [58]. Our interest here is in the comparison of different methods (RHF and DFT) to describe the electron

245

distribution in 4-HTMDBN is broadly as possible and to assess the sensitivity of the calculated charges in the choice of the quantum chemical method. The calculated atomic charge values from the natural population analysis (NPA) and Mullikan population analysis (MPA) procedures using the RHF and DFT methods are listed in Table 5. It is evident from [59], that results from calculations of atomic charges from the population analyses have shown that NPA charges, which are based on electronic orbitals are not sensitive to the basis set while MPA method shows basis set dependency. The natural population analysis of 4-HTMDBN shows that the presence of 4 active carbon atoms in the nitrogen moiety [C1 = 0.27206 (DFT) and 0.32100 (HF)]; [C14 = 0.21680 (DFT), 0.29414 (HF)]; C21 = 0.27112 (DFT),0.31979 (HF)]; and C12 = 0.13296 (DFT) 0.1956 (HF)] possess positive charge due to the large negative charge on the nitrogen atoms [N8 = 0.28319 (DFT); 0.33654 (HF)]; [N10 = 0.16176(DFT); 0.21671(HF)]; N11 = 0.29064 (DFT); 0.32615 (HF); [N13 = 0.49215(DFT); 0.56065 (HF)]; [N22 = 0.28566 (DFT); 0.33759 (HF)]. Also, the NPA of 4-HTMDBN shows there is no difference in charge distribution observed on all hydrogen atoms. The large positive charges on the hydrogen atoms are due to the large negative charges accumulated on the associated carbon atoms. Frontier molecular orbitals The Frontier molecular orbital plays an important role in the electric and optical properties, as well as in the UV–Vis spectra and chemical reaction [60]. Absorption maximum (kmax) of our title molecule calculated by ZINDO method is compared with the kmax value of the recorded UV–Vis spectra shown in Fig 7. The calculation of molecular orbital geometry shows that the visible absorption maxima of the 4-HTMDPN correspond to the electronic transition from HOMO to LUMO. The kmax is a function of substitution, the more electrons pushed into the ring, the larger kmax [61]. The calculated results involving the vertical excitation energies, oscillatory strength and wavelength shown in Table 6 are compared with measured experimental wavelength. In Table 6, we compare excitation energies n ? p* and p ? p* transitions with the experimental values and present the results obtained using ZINDO method. As expected, the ZINDO method overestimates excitation energy of the p ? p* transitions with the experimental values and present the results obtained using ZINDO method. The difference between the experimental band maxima and ZINDO maxima and ZINDO values deviates from 43 nm (n ? p*). Since, the ZINDO results are of a qualitative character, we compare the results for the second singlet state S2 (p ? p*) with differences in the value of about 33 nm. Fig. 8 shows the distributions and energy levels of the HOMO  1, HOMO, LUMO and LUMO + 1 orbital’s computed at the B3LYP/6-31G(d,p) level for the 4-HTMDBN. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are very important parameters for quantum chemistry. We can determine the way the molecule interacts with other species; hence they are called the frontier orbitals. HOMO, which can be thought the outermost orbital containing electrons, tends to give these electrons such as an electron donor. On the other hand; LUMO can be thought the innermost orbital containing free places to accept electron [62]. Fig. 8 shows the distribution and energy levels of the HOMO  1, HOMO, LUMO and LUMO + 1 orbitals computed at the B3LYP/6-31G(d,p) level for the 4-HTMDBN. According to B3LYP/6-31G(d,p) calculation the energy band gap (DE) (translation from HOMO to LUMO) of the molecules is about 5.3038 eV presented in Table S4 (Supplementary material). The energy gap reveals the important stability for structure [63] and it reflects the chemical activity of the molecule. The highest occupied molecule orbitals are localized mainly on

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Table 4 Second-order perturbation theory analysis of Fock matrix in NBO Basis for 4-HTMDBN. Donor (i)

ED (i) (e)

Type

C1–C2

1.97225

r

C1–N8 C1–N8 C2–C3

1.99351 1.98448 1.95586

r p r

C2–C7

1.95605

r

C4–C5

1.96777

r

C4–C5

1.64479

p

C5–C6

1.96654

r

C6–C7

1.97288

r

C6–C7

1.65647

p

C6–H25

1.97594

r

C7–H26

1.97756

r

C9–H27

1.96518

r

N11–C12 N11–C12

1.98346 1.84683

r p

N13–C14

1.97810

r

C15–C16

1.96632

r

C15–C20

1.96643

r

C15–C20

1.65321

p

C16–C17

1.97306

r

C16–C17

1.66119

p

C16–H30

1.97518

r

C17–H31

1.97748

r

C18–C19

1.95537

r

C18–C19

1.63018

p

C18–C21

1.97270

r

C19–C20

1.97039

r

C19–H32

1.97741

r

C20–H33

1.76801

r

Acceptor (j) C1–N8 C2–C3 C2–C7 C1–C2 C2–C3 C1–C2 C1–N8 C2–C7 C4–C5 C6–C7 C1–C2 C1–N8 C2–C3 C3–C4 C5–C6 C2–C3 C6–C7 C4–C5 C6–C7 C1–C2 C2–C7 C5–C6 C5–C9 C2–C3 C4–C5 C2–C7 C4–C5 C2–C3 C5–C6 C5–C6 C12–H28 C9–N10 N13–C14 C14–H29 C9-N10 C12–H28 C12–N13 C14–H29 C20–H33 C15–C20 C16–C17 C15–C16 C19–C20 C16–C17 C18–C19 C9–C15 C15–C16 C17–C18 C15–C20 C18–C19 C15–C20 C17–C18 C18–C19 C18–C21 C21–N22 C15–C16 C18–C19 C17–C18 C18–C21 C21–N22 C15–C20 C16–C17 C17–C18 C18–C19 C21–N22 C9–C15 C15–C20 C18–C19 C15–C20 C17–C18 N13–C14 C14–H29 C15–C16 C18–C19

Type *

r r* r* r* p* r* r* r* p* p* r* r* r* r* r* p* p* r* r* r* r* r* r* p* p* r* r* r* r* r* r* r* p* r* r* r* r* r* r* r* r* r* r* p* p* r* r* r* p* p* r* r* r* r* r* r* r* r* r* r* p* p* r* r* r* r* r* r* r* r* r* r* r* r*

ED (j) (e)

E(2)a (kJ mol1)

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

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

0.01172 0.03342 0.03338 0.03554 0.38604 0.03554 0.01172 0.03338 0.34122 0.28702 0.03554 0.1172 0.03342 0.01744 0.02915 0.38604 0.28702 0.02768 0.01760 0.03554 0.03338 0.02915 0.03751 0.38604 0.34122 0.03338 0.02768 0.03342 0.02915 0.02915 0.02835 0.05258 0.41863 0.20318 0.05258 0.0.02835 0.02741 0.020318 0.25865 0.02833 0.01754 002866 0.02058 0.29056 0.37830 0.03768 0.02866 0.03667 0.34977 0.37830 0.02833 0.03367 0.03877 0.03645 0.09227 0.02866 0.03877 0.03367 0.03645 0.01189 0.34977 0.29056 0.03367 0.03877 0.01189 0.03768 0.02833 0.03877 0.02833 0.03367 0.02020 0.20318 0.02866 0.03877

9.19 5.37 5.36 9.90 12.10 6.08 5.67 6.85 20.02 22.66 6.09 5.67 6.86 4.33 6.12 23.56 19.98 6.11 4.52 3.63 4.23 5.11 4.46 21.58 24.33 4.13 5.22 5.17 4.50 4.06 4.44 9.03 17.68 4.12 6.07 5.61 5.49 39.87 305.12 7.04 4.33 5.82 5.12 19.67 22.91 4.60 5.18 4.22 24.43 21.13 5.32 4.16 7.13 6.04 5.65 4.57 5.15 6.80 6.25 5.75 19.94 23.20 5.29 5.20 9.18 4.76 5.92 4.28 5.03 5.10 7.33 209.15 4.91 4.71

1.71 1.44 1.44 1.74 0.37 1.45 1.66 1.39 0.32 0.32 1.45 1.66 1.39 1.40 1.40 0.32 0.32 1.40 1.40 1.45 1.39 1.39 1.15 0.32 0.32 1.17 1.18 1.17 1.18 1.18 1.46 1.19 0.36 1.75 1.20 1.36 1.06 1.28 1.35 1.40 1.41 1.40 1.42 0.32 0.32 1.15 1.40 1.39 0.31 0.32 1.18 1.17 1.39 1.45 1.66 1.18 1.17 1.38 1.44 1.66 0.31 0.31 1.44 1.44 1.71 1.14 1.38 1.38 1.17 1.17 1.17 1.31 1.07 1.07

0.112 0.078 0.078 0.118 0.065 0.084 0.087 0.087 0.072 0.077 0.084 0.087 0.087 0.070 0.083 0.078 0.072 0.083 0.071 0.065 0.068 0.075 0.064 0.075 0.078 0.062 0.070 0.070 0.065 0.062 0.072 0.093 0.077 0.080 0.077 0.078 0.073 0.205 0.077 0.089 0.070 0.081 0.076 0.072 0.078 0.065 0.076 0.068 0.078 0.074 0.071 0.062 0.089 0.084 0.087 0.066 0.070 0.087 0.085 0.088 0.071 0.078 0.078 0.077 0.112 0.066 0.081 0.069 0.069 0.069 0.087 0.470 0.068 0.067

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a b c

ED (i) (e)

Type

C21–N22

1.99353

r

LP(1) N8 LP(1) N11

1.97085 1.92418

r r

LP(1) N13

1.90543

r

LP(1) N22

1.97083

r

Acceptor (j) C20–H33 C18–C21 C17–C18 C18-C19 C1–C2 N10–C14 C12–N13 N10–C14 N11–C12 C14–H29 C18–C21

Type

ED (j) (e)

*

r r* r* r* r* r* r* r* r* r* r*

E(2)a (kJ mol1)

0.25865 0.03645 0.03367 0.03877 0.03554 0.06030 0.02741 0.06030 0.02430 0.20318 0.03645

22.59 9.85 4.25 4.21 14.31 12.10 6.36 11.88 9.53 4.03 14.29

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

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

1.39 1.74 0.97 0.97 1.21 0.98 1.05 0.93 0.98 1.21 1.21

0.159 0.118 0.058 0.057 0.118 0.098 0.074 0.095 0.088 0.064 0.118

Energy of hyper conjugative interaction (stabilization energy). Energy difference between donor and acceptor i and j NBO orbital. Fock matrix element between i and j NBO orbital.

Table 5 Natural atomic charges (eu) of 4-HTMDBN. Atom with numbering

MPA

NPA

HF/6-31G(d.p)DFT

DFT/6-31G(d,p)

HF/6-31G(d,p)

DFT/6-31G(d,p)

C1 C2 C3 C4 C5 C6 C7 N8 C9 N10 N11 C12 N13 C14 C15 C16 C17 C18 C19 C20 C21 N22 H23 H24 H25 H26 H27 H28 H29 H30 H31 H32 H33

0.1819 0.0641 0.1073 0.1615 0.0452 0.1391 0.1072 0.4563 0.1112 0.4469 0.2804 0.2083 0.5360 0.4499 0.0593 0.1390 0.1164 0.0747 0.0994 0.2510 0.1758 0.4574 0.1970 0.1714 0.1724 0.1984 0.1918 0.1654 0.0230 0.1764 0.1993 0.1944 0.3568

0.1324 0.2426 0.0900 0.1343 0.2071 0.1165 0.0873 0.4714 0.0709 0.2762 0.2721 0.1832 0.4696 0.4210 0.0784 0.1141 0.1013 0.2680 0.1402 0.1596 0.1208 0.4740 0.1190 0.0991 0.0999 0.1205 0.1401 0.1074 0.0850 0.1000 0.1197 0.1116 0.3917

0.3210 0.2198 0.1367 0.2247 0.0295 0.2203 0.1370 0.3365 0.0212 0.2167 0.3262 0.1957 0.5607 0.2941 0.0487 0.2260 0.1348 0.2240 0.1282 0.1753 0.3198 0.3376 0.2530 0.2408 0.2416 0.2538 0.2676 0.2187 0.2067 0.2441 0.2543 0.2435 0.1491

0.2721 0.1993 0.1576 0.2189 0.0379 0.2162 0.1577 0.2832 0.0674 0.1618 0.2906 0.1330 0.4922 0.2168 0.0618 0.2196 0.1588 0.2018 0.1555 0.1505 0.2711 0.2857 0.2578 0.2464 0.2468 0.2585 0.2804 0.2234 0.2094 0.2486 0.2586 0.2472 0.1461

eu = Electron units.

both the phenyl ring. On the other hand, the lowest unoccupied molecule orbitals are localized mainly on pyridine ring.

HOMO-LUMO energy gap ¼ 5:3038 eV

HOMO energy ¼ 7:43475 eV

Other molecular properties

LUMO energy ¼ 2:13094 eV

The quantum chemical properties of molecule as whole make us to know how to find the energy states of the molecule or subsidiaries that used for molecular electronic. Chemical bonds are a source of energy and the movement of molecules in space is kinetic energy. The vibrations and rotations of molecules is another source of chemical energy along with the chemical reaction which is a rearrangement of atoms. Density functional theory has been to be successful in providing insights into the chemical reactivity and selectivity, in terms of global parameters such as electronegativity (v), hardness (g) and softness (r). Thus for an electron

Table 6 UV–Vis excitation energies (DE), oscillatory strength (f) and wavelength (k) for 4HTMDBN. States

S1 S2

Observed

ZINDO

kabs (nm)

DE (eV)

k (nm)

f

245.0 235.0

4.4581 4.6950

278.11 264.08

0.0013 0.0001

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system with total electronic energy (E) and an external potential V(r), Chemical potential (q) known as the first derivative of the E with respect N at V(r) [64].



v ¼ q ¼ 

 @E VðrÞ @N

Hardness (g) has been defined as the second derivative of the E with respect N at V(r) property which measures both the stability and reactivity of a molecule [65].

g¼

@2E @N 2

! VðrÞ ¼ 



 @q VðrÞ @N

DE = EA  IP. Electronegativity is a chemical property that describes the ability of an atom or a functional group to attract electrons or electron density towards itself. The ionization potential calculated by HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods for 4-HTMDBN is 9.7733 eV and 7.43475 eV, respectively. Considering, the chemical hardness, large HOMO–LUMO gap means a hard molecule and small HOMO–LUMO gap means a soft molecule. One can also relate the stability of the molecule to hardness, which means that the molecule with least HOMO–LUMO gap means it is more reactive. Local reactivity descriptors

where E is the electronic energy, N is the number of electrons, and V(r) is the external potential due to the nuclei and q is chemical potential. The electronegativity and chemical hardness of the molecule were calculated using Koopmans’s theorem [66] and are given by

Fukui functions (f k , fk, fk0) and Local softness (sk+, sk, sk0) [73,74] for selected atomic sites in 4-HTMDPN have been listed in Table 7. Using Hirshfeld atomic charges of neutral, cation, and anion states of 4-HTMDPN, Fukui functions are calculated using the following equations.

v ¼ ½IP þ EA=2 ¼ ½ELUMO þ EHOMO =2

fkþ ¼ qk ðN þ 1Þ  qk ðNÞ for nucleophilc attack

g ¼ ½IP  EA=2 ¼ ½ELUMO  EHOMO =2

fk ¼ qk ðNÞ  qk ðN  1Þ for electrophilic attack

where IP  E(HOMO), EA  E(LUMO), IP = Ionization potential (eV), EA = electron affinity (eV). Recently, Parr et al. [67] introduces a new global chemical reactivity parameter and is called an electrophilicity index (x). It is defined as [68],

x ¼ q2 =2g This was proposed as a measure of the electrophilic power of a molecule. Global softness can also be defined as [69],

r ¼ 1=g The total energy change is defined as DET = g/4 All the above mentioned quantum chemical properties calculated by using HF and DF/B3LYP methods with 6-31G(d,p) basis set and are shown in Table S4 (Supplementary material). The usefulness of this new reactivity quantity has been recently demonstrated in understanding the toxicity of various pollutants in terms of their reactivity and site selectivity [70–72]. The calculated value of electrophilicity index describes the biological activity of 4-HTMDBN. A molecule or atoms that possess positive electron affinity is called an electron acceptor and may undergo charge transfer reactions. The electron donating power of a donor molecule is measured by its ionization potential which is the energy required to remove an electron from the HOMO .The overall energy balance (DE), i.e., energy gained or lost, in an electron donor–acceptor transfer is determined by the difference between the acceptor’s electron affinity (EA) and the ionization potential (IP) as

þ

fk0 ¼

1 ½q ðN þ 1Þ  qk ðN  1Þ for radical attack 2 k

In these equations, qk is the atomic charge (evaluated from Mulliken population analysis, electrostatic derived charge, etc.) at the kth atomic site is the neutral (N), anionic (N + 1) or cationic (N  1) chemical species. Inorder to solve the negative Fukui function problem, different attempts have been made by various groups [75–77]. Kolandaivel et al. [78] introduced the atomic descriptor to determine the local reactive sites of the molecular system. In the present study, the optimized molecular geometry was utilized in singlepoint energy calculations, which have been performed at the DFT for the anions and cations of the title compound using the ground state with doublet multiplicity. The individual atomic charges calculated by Mulliken population analysis (MPA) have been used to calculate the Fukui function. Inorder to confirm that the atomic descriptor would produce the reactive sites without disturbing the trend; we have performed the calculation for the reactive sites of the stable structures of 4-HTMDPN. Local softness is calculated using the following equations þ



0

sþk ¼ Sf k ; sk ¼ Sf k ; s0k ¼ Sf k

Homo (-7.43475ev)

Homo -1 (-7.60210ev) Fig. 7. Absorption Spectrum of 4-HTMDBN.

Lumo (-2.13094ev)

Lumo +1(-1.81311ev)

Fig. 8. Atomic orbital composition of the frontier molecular orbital for 4-HTMDBN.

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where +, , 0 signs show nucleophilic, electrophilic and radical attack, respectively. It has been found that MPA schemes predict C14 has higher fk value indicates the possible site for electrophilic attack. From the values reported in Table S4 (Supplementary material), MPA schemes predict the reactivity order for the electrophilic case as C14 > C18 > C2 > C12 > C5 > C1 > C21. The observation of the  reactive sites by ðsf Þk is found almost identical to fk . Even though the (sf)k values are numerically less it should be worth noting that the values are positive and the ordering of the reactivity has not changed in any case. The calculated fk+ value predicts that the possible sites for nucleophillic attack is C14, C18,C2, C5 and C10 site and the radical attack was predicted at C1, C12, C14 and C21 site. From the tabulated values it is evident that reactivity order for the nucleophilic case was C14 > C18 > C2 > C5 > C10. If one compares the three kinds of attacks it is possible to observe that, electrophilic attack is bigger reactivity comparison with the nucleophilic and radical attack.

Molecular electrostatic potential The molecular electrostatic potential (MEP) is the most useful electrostatic property to study the relation between the structure and activity. The MEP has been also employed as an information tool of chemistry to describe different physical and chemical features, including non-covalent interactions in complex biological system. The electrostatic potential created by the nuclei and electrons of a molecule in the surrounding space is well established as a guide to the interpretation and prediction of molecular behavior. It has been shown to be a useful tool in studying both electrophilic and nucleophilic processes [78–80], in particular, to be well suited for studies that involve the identification of key features necessary for the ‘‘recognition’’ of one molecule by another. At any given point r(x,y,z) in the vicinity of a molecule, MEP V(r) is defined in terms of the interaction energy between the electrical energy generated from the molecule electrons and nuclei and a positive test charge (a proton) [81,82]. At point r, the MEP, V(r) is given by

Table 7 Condensed Fukui function for atoms of 4-HTMDBN. 

þ

0



þ

0

Atom

fk

fk

fk

ðsfÞk

ðsfÞk

ðsfÞk

C1 C2 C3 C4 C5 C6 C7 N8 C9 N10 N11 C12 N13 C14 C15 C16 C17 C18 C19 C20 C21 N22

0.1867 0.2564 0.0749 0.1317 0.2086 0.1166 0.0743 0.4070 0.0765 0.2755 0.2250 0.2243 0.4114 0.4863 0.0941 0.1038 0.0824 0.2774 0.1134 0.1634 0.1489 0.4265

0.0602 0.2180 0.1061 0.1432 0.1888 0.1187 0.1091 0.5501 0.0670 0.2722 0.2715 0.1708 0.4885 0.4117 0.0591 0.1175 0.1230 0.2426 0.1641 0.1607 0.0448 0.5534

0.2426 0.1063 0.0822 0.1198 0.1152 0.1087 0.0804 0.4630 0.0376 0.2852 0.2666 0.2182 0.4595 0.2739 0.0948 0.1122 0.0766 0.1068 0.0809 0.1215 0.2459 0.4592

0.0066 0.0124 0.0011 0.0033 0.0082 0.0026 0.0010 0.0312 0.0011 0.0143 0.0095 0.0095 0.0319 0.0446 0.0017 0.0020 0.0013 0.0145 0.0024 0.0050 0.0042 0.0343

0.0007 0.0090 0.0021 0.0039 0.0067 0.0027 0.0022 0.0571 0.0008 0.0140 0.0139 0.0055 0.0450 0.0319 0.0007 0.0026 0.0029 0.0111 0.0051 0.0049 0.0004 0.0577

0.0111 0.0021 0.0013 0.0027 0.0025 0.0022 0.0012 0.0404 0.0003 0.0153 0.0134 0.0090 0.0398 0.0141 0.0017 0.0024 0.0011 0.0022 0.0012 0.0028 0.0114 0.0398

Thermodynamic properties On the basis of vibrational analysis and statistical thermodynamics, the standard thermodynamic functions, heat capacity (C0p,m) entropy ðS0m Þ, and enthalpy ðH0m Þ were calculated using Perl script THERMO.PL [83] and are listed in Table 8, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 1100 K due to the fact that the molecular vibrational intensities increase with temperature. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures are fitted by quadratic formulas and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9994, 0.9999 and 0.9997, respectively. The corresponding fitting equations are as follows and the correlation graph of those are shown in Fig. 10.

C0p;m ¼ 5:6926 þ 1:0093T  4:7144  10  4T2 ðR2 ¼ 0:9994Þ

VðrÞ ¼ ZA =jRA  rj

S0m ¼ 265:2598 þ 1:0325T  2:4546  10  4T2 ðR2 ¼ 0:9999Þ

where, V(r0 ) is the electron density at r0 , ZA is the charge on nucleus a located at RA. The first term is due to the nuclear charge, the second, to the electronic distribution. MEP surface diagram is used to understand the reactive behavior of a molecule, in that negative regions can be regarded as potential electrophilic sites, whereas the positive regions are nucleophilic centers. In Fig. 9, electrophilic site is presented by negative (red color) region and nucleophilic center is shown by the positive (blue color) regions of MEP. The different values of the electrostatic potential at the surface are represented by different colors. Potential increase in the order red < orange < yellow < green < blue. As can be seen from the Fig. 9, this molecule has several possible sites for electrophilic attack. Negatively electrophilic potential regions are mainly localized over the N13 and N11 atoms. The negative V(r) values are 0.4922 a.u for N13 atom which is the most negative region, 0.02906 a.u for N11 atom. However, a maximum positive region is localized on C1 and C2 atoms bonded to C2 and C18 with values +0.2721 a.u and 0.2711 a.u, respectively. According to these calculated results, the MEP shows that the negative potential sites are on nitrogen atoms as well as the positive potential sites are around the hydrogen atoms.

H0m ¼ 6:1831 þ 0:0847T þ 2:9678  10  4T2 ðR2 ¼ 0:9997Þ All the thermodynamic data supply helpful information for the further study on the HPCBA. 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 [84]. The variation in zero-point vibrational energies (ZPVEs) seems to be significant. The values of some thermodynamic parameters (such as zero-point vibrational energy, thermal energy, specific heat capacity, rotational constants, entropy and dipole moment) of 4HTMDPN by HF and B3LYP with 6-31G(d,p) method at room temperature are listed in the Table S5 (Supplementary material). The ZPVE of 4HTMDPN is 167.0595 kcal mol1 obtained at the HF/631G(d,p) whereas 155.1290 kcal mol1 is obtained at B3LYP/631G(d,p) method. Dipole moment reflects the molecular charge distribution and is given as a vector in three dimensions. Therefore, it can be used an illustrator to depict the charge movement across the molecule [85]. Direction of the dipole moment vector in a molecule depends on the centers of negative and positive charges. Dipole moments are strictly identified for neutral molecules. For

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charged systems, its value depends on the choice of origin and molecular orientation. As a result the dipole moment of title molecule was observed as 2.7301D with B3LYP/6-31G(d,p) method. Conclusions

Fig. 9. Molecular electrostatic potential of 4-HTMDBN.

Table 8 Thermodynamic properties at different temperatures at the B3LYP/6-31G(d,p) level for 4-HTMDBN. Temperature (K)

C0p;m (cal mol1 K1)

S0m (cal mol1 K1)

H0m (kcal mol1)

100.00 150.00 200.00 250.00 298.15 300.00 350.00 400.00 450.00 500.00 550.00 600.00 650.00 700.00 750.00 800.00 850.00 900.00 950.00 1000.00

119.85 152.76 188.30 226.83 265.56 267.06 307.18 345.69 381.64 414.59 444.59 471.45 495.78 517.73 537.60 555.61 572.01 586.97 600.65 613.20

378.41 433.18 481.91 528.02 572.92 617.12 617.12 660.67 703.49 745.44 786.38 826.23 864.94 902.50 938.51 974.19 1008.37 1041.50 1073.60 1104.74

8.11 14.92 23.43 33.80 45.65 46.14 60.50 76.84 95.03 114.95 136.44 159.35 183.54 208.89 235.28 262.61 290.81 319.79 349.49 379.84

This study demonstrates that scaled DFT (B3LYP) calculations are powerful approach for understanding the vibrational spectra of the title molecule. The FT-IR, FT-Raman along with NMR and UV-spectral studies of 4-HTMDPN were carried out for the first time. A complete vibrational and molecular structure analysis have been performed based on the quantum mechanical approach by NCA and HF/DFT calculation. The difference between the observed and scaled wavenumber values of most of the fundamentals are very small. Therefore, the assignments made at DFT level of theory with only reasonable deviations from the experimental values seem to be correct. Theoretical 1H and 13C chemical shift values were carried out and compared with experimental data, good agreement for both 1H and 13C. NBO analysis indicating the strong intramolecular hyperconjugative interaction within the molecule and stability of the molecule. The calculated first hyperpolarizability of 4-HTMDPN is much greater than that of urea. This indicates that the title compound is best material for NLO applications. The Mulliken charges and natural atomic charges of the title molecule have been studied by both the HF and DFT methods. The calculated HOMO and LUMO energies can be used to semiquantitatively estimate the ionization potential, electron affinity, electronegativity, electrophilicity index, hardness and chemical potential. The predicted MEP shows the negative electrophilic potential regions are mainly localized over the nitrogen atoms. The theoretically constructed FT-IR and FT-Raman shows good correlation with experimentally observed FT-IR and FT-Raman spectra. Thermodynamic properties in the range from 100 K to 1000 K are obtained. The gradients of Cpm, Sm, Hm and Vibrational intensity increases with increase of temperature. Fukui function, local softness and electrophilicity indices for selected atomic sites in 4-HTMDPN have been calculated. 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.2013.10.007. References

Fig. 10. Correlation graph of Thermodynamic parameters and temperature for 4HTMDBN.

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