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Synthesis, molecular structure, spectral analysis and nonlinear optical studies on 4-(4-bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5-amine: A combined experimental and DFT approach
Journal of Molecular Structure 1106 (2016) 89e97
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, molecular structure, spectral analysis and nonlinear optical studies on 4-(4-bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5amine: A combined experimental and DFT approach € lu b, Yusuf Atalay a, Omer Tamer a, Barıs¸ Seçkin Arslan b, Davut Avcı a, *, Mehmet Nebiog c Bünyemin Ços¸ut a b c
Sakarya University, Department of Physics, Arts and Sciences Faculty, 54187 Sakarya, Turkey Sakarya University, Department of Chemistry, Arts and Sciences Faculty, 54187 Sakarya, Turkey Gebze Technical University, Department of Chemistry, 41400 Gebze, Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 August 2015 Received in revised form 23 October 2015 Accepted 26 October 2015 Available online 29 October 2015
4-(4-bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5-amine (BPTBMPA) crystal was synthesized for the first time and its structural characterization was performed by X-ray diffraction method. The spectroscopic characterization was also performed by the applying of FT-IR, UVeVis, 1H and 13C NMR spectroscopies. In order to support experimental results, density functional theory calculations have been performed. All of the obtained theoretical results are in a perfect agreement with the experimental ones. The negative HOMO and LUMO energies demonstrated that the molecular structure of BPTBMPA is stable. The small energy gap between the HOMO and LUMO is an indicator of intramolecular charge transfer which is responsible for nonlinear optical properties. Natural bond orbital analysis also indicates the presence of molecular charge transfer within BPTBMPA. Obtained chemical hardness parameter demonstrates that BPTBMPA has considerable electron donor groups. Finally, it has been showed that BPTBMPA exhibits considerable nonlinear optical properties. © 2015 Elsevier B.V. All rights reserved.
Keywords: 4-(4-Bromophenyl)-1-tert-butyl-3-methyl1H-pyrazol-5-amine X-ray NMR FTIR DFT Nonlinear optics
1. Introduction Pyrazoles and its derivatives, a class of well-known nitrogen heterocycles, have attracted considerable interest in the pharmaceutical and agrochemical industries because of their diverse biological activities, such as, anti-inflammatory [1], antiviral [2], antimicrobial [3], anticonvulsant [4], antitumor [5], fungicidal activities [6] and antihistaminic [7]. As pyrazole derivatives rarely exist in nature, probably, due to the difficulty in the construction of NeN bond by living organisms, their availability particularly depends on the synthetic methods [8]. One of the most important derivatives of pyrazoles is 5-aminopyrazoles and their chemistry has been reviewed several times recently [9e12]. The most versatile method available for the synthesis of 5-aminopyrazoles involves the condensation of b-ketonitriles with hydrazines. Besides of the well-known biological activities, pyrazoles
* Corresponding author. E-mail address: [email protected] (D. Avcı). http://dx.doi.org/10.1016/j.molstruc.2015.10.084 0022-2860/© 2015 Elsevier B.V. All rights reserved.
derivatives substituted with electron donor and acceptor groups exhibit considerable nonlinear optical properties [13e15]. Up to now, a number of new organic crystals have been discovered with the aid of experimental and computational molecular engineering approaches and shown to have potential applications in nonlinear optics. But, in order to satisfy day to day increasing technological requirements, the search for new NLO materials has been still receiving great interest. It is well known that NLO properties of organic molecules depend on the intermolecular charge transfer [16e18]. At the same time, the molecular hydrogen bonding has been found to play an important role in adjusting NLO properties. Additionally, the substitution of conjugated p system with appropriate donor acceptor groups increase the asymmetric charge distribution in the ground state and excited state, and this leads to improve NLO properties [19,20]. So, 4-(4bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5-amine (BPTBMPA) molecule, which is an substituted pyrazole, has been considered as an interesting molecule due to the presence of pyrazole ring, electron donor NH2 and CH3 groups and Cl atom. Therefore, BPTBMPA may be exhibit considerable NLO properties.
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In this paper, we have synthesized BPTBMPA crystal for the first time and its crystal structure has been characterized by X-ray diffraction method. The spectroscopic properties of BPTBMPA have been evaluated by the applying of FT-IR, NMR and UVeVis spectroscopies as well as density functional theory (DFT) calculations. Additionally, natural bond orbital analysis and the investigations of NLO properties for BPTBMPA have been performed by DFT method. 2. Experimental details 2.1. Synthesis of 4-(4-bromophenyl)-1-tert-butyl-3-methyl-1Hpyrazol-5-amine To a solution of 2-(4-bromophenyl)-3-oxobutanenitrile 1 (2 mmol, 0.476 g) and tert-butylhydrazine hydrochloride (1.2 eq., 0.299 g) in toluene (10 mL) was added acetic acid (% 10 mol, 0.0115 mL) and the mixture was heated to reflux temperature for 5 h. The synthesis scheme for BPTBMPA was presented in Fig. 1. After completion of the reaction as monitored by TLC, the solvent was removed under reduced pressure. To this crude concentrate, water was added and extracted into ethyl acetate. The organic layer was dried over anhydrous sodium sulphate, concentrated under reduced pressure to give crude 2. It was crystallized from methanol and yielded 81% (colorless crystals, mp 161e162 C). 2.2. Instrumentation FT-IR spectrum for BPTBMPA was recorded on a PerkineElmer FT-IR spectrophotometer at the region of 4000e600 cm1. 1H and 13 C NMR spectra were measured on a Varian Infinity Plus spectrometer at 300 and 75 Hz, respectively. 1H and 13C chemical shifts are referenced to the internal deuterated solvent. The UVevis absorption spectrum was examined in the range 200e800 nm using a Shimadzu UV-2600 spectrophotometer in dichloromethane solvent. 2.3. X-ray crystal structure determination The solid-state structure of BPTBMPA has been confirmed by Xray diffraction analysis. Data have been obtained with Bruker APEX II QUAZAR three-circle diffractometer. Indexing was performed using APEX2 [21]. Data integration and reduction were carried out with SAINT [22]. Absorption correction was performed by multiscan method implemented in SADABS [23]. The Bruker SHELXTL [24] software package was used for structure solution and structure refinement. All non-hydrogen atoms were refined anisotropically using all reflections with I > 2s(I). Aromatic C-bound H atoms were positioned geometrically and refined using a riding mode. Crystallographic data and refinement details of the data collection for BPTBMPA are given in Table 1. The selected bond lengths and bond angles are given in Table 2. Final geometrical calculations were performed using PLATON software [25]. MERCURY software [26] was used for visualization of the cif files. The important conditions for the data collection and the structure refinement parameters of BPTBMPA are also given in Table 1.
Table 1 Crystal data and refinement parameters for BPTBMPA. CCDC Empirical Formula Formula weight (g.mol1) Temperature (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) a( ) b( ) g( ) Crystal size (mm) V (Å3) Z Density (g/cm3) m (mm1) F(000) q range for data collection ( ) h/k/l Reflections collected Independent reflections Absorption correction Data/restraints/parameters Goodness-of-fit on F2 (S) Final R indices [I > 2s(I)] R indices (all data) Largest diff. peak and hole (e.Å3)
C14H18BrN3 308.22 173 (2) 0.71073 monoclinic P21/c 5.9314(10) 20.050(3) 11.8114(16) 90 96.169(11) 90 0.345 0.109 0.107 1396.5(4) 4 1.446 2.930 632 2.03e26.73 7/6, 23/25, 14/14 12537 2964 [R(int) ¼ 0.0840] multi-scan 2964/2/173 1.038 R1 ¼ 0.0358, wR2 ¼ 0.0877 R1 ¼ 0.0499, wR2 ¼ 0.0936 0.437 and 0.757
Table 2 The experimental and theoretical bond lengths (Å) and angles ( ) for BPTBMPA. Bond lengths
X-ray
HSEH1PBE
Bond angles
X-ray
HSEH1PBE
Br1eC1 C1eC6 C1eC2 C2eC3 C3eC4 C4eC5 C4eC13 C5eC6 C7eN2 C7eC10 C7eC9 C7eC8 C11eC12 C12eN3 C12eC13 C13eC14 C14eN2 C14eN1 N2eN3 R2
1.909(3) 1.369(4) 1.378(4) 1.384(4) 1.394(4) 1.397(3) 1.474(3) 1.385(4) 1.485(3) 1.518(4) 1.521(4) 1.524(4) 1.490(4) 1.330(3) 1.404(4) 1.384(3) 1.348(3) 1.381(3) 1.381(3)
1.898 1.387 1.389 1.388 1.401 1.402 1.461 1.389 1.480 1.532 1.531 1.526 1.490 1.316 1.418 1.392 1.356 1.390 1.356 0.99202
C6eC1eC2 C6eC1eBr1 C1eC2eC3 C3eC4eC13 C1eC6eC5 N2eC7eC10 N2eC7eC9 C10eC7eC9 N2eC7eC8 N3eC12eC13 N3eC12eC11 C14eC13eC12 C14eC13eC4 C12eC13eC4 N2eC14eN1 N2eC14eC13 C14eN2eN3 C14eN2eC7 C12eN3eN2
121.7(2) 118.7(2) 118.7(3) 122.3(2) 118.9(2) 110.1(2) 108.0(2) 111.7(2) 108.6(2) 111.7(2) 120.0(2) 104.6(2) 126.7(2) 128.7(2) 123.9(2) 107.8(2) 110.9(2) 129.4(2) 105.0(2)
120.7 119.6 119.4 121.4 119.2 109.7 108.8 111.5 109.4 111.3 120.1 104.0 126.6 129.4 124.2 107.3 111.1 129.0 106.3 0.99292
3. Computational details All of the calculations for BPTBMPA have been performed by using Gaussian 09 Rev: D.01 program [27], and the output files have
Fig. 1. The synthesis scheme for BPTBMPA.
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
been visualized by means of GaussView 05 program [28]. The ground state geometry and IR spectrum have been obtained by using HSEH1PBE (The recommended version of the full HeydScuseria-Ernzerhof functional) [29,30] level of density functional theory (DFT) with 6-311G(d,p) basis set. BPTBMPA has been also optimized in chloroform in order to calculate 1H and 13C NMR chemical shifts. The GIAO approach [31,32] which is one of the most common approaches for calculating nuclear magnetic shielding tensors has been used to calculate NMR spectra. BPTBMPA has been optimized in dichloromethane, and the UVevis spectrum has been calculated in the same solvent. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, absorption wavelengths, oscillator strengths and molecular orbital contributions to the electronic transitions for BPTBMPA have been calculated with the time dependent DFT (TD-DFT) method starting from the ground-state geometry optimized in the dichloromethane solvent. Natural bond orbital (NBO) calculation has been performed to understand various second order interaction between the filled orbital of one subsystem and vacant orbital of another subsystem which is measure of the molecular delocalization or hyperconjugation using NBO 3.1 program [33]. The NLO properties of BPTBMPA have been investigated by the determining of polarizability (a) and first order hyperpolarizability (b). 4. Results and discussion 4.1. Description of molecular structure The BPTBMPA crystal, an ORTEP 3 diagram (50% probability) with the atom labeling for synthesized crystal is shown in Fig. 2a, crystallizes in P21/c space group. The BPTBMPA crystal belongs to monoclinic system with the following cell dimensions: a ¼ 5.9314(10) Å, b ¼ 20.050(3) Å, c ¼ 11.8114(16) Å,
91
b ¼ 96.169(11) , Z ¼ 4 (Table 1). The experimental bond lengths and selected bond angles for BPTBMPA crystal are given in Table 2, as compared with theoretical ones obtained at HSEH1PBE level. The molecular structure of BPTBMPA contains pyrazole and pyridine rings, and these rings are planar with a maximum deviation of 0.9(3) and 1.4(4) . The CeC bond lengths in the phenyl rings are observed in the range of 1.369(4)e1.397(3) Å (XRD) and calculated in the range of 1.387e1.402 Å (HSEH1PBE). The bond lengths are consistent with previously phenyl ring-containing studies [34]. The C12eN3 and C14eN2 bonds have double bond character with the bond lengths of 1.330(3) and 1.348(3) Å, while other bonds in pyrazole ring (C12eC13, C13eC14 and N2eN3) have a single bond character with the bond lengths of 1.404(4), 1.384(3) and 1.381(3) Å, respectively. The methyl group CeC bond lengths are in the range of 1.490(4)e1.524(4) Å (XRD) and 1.490e1.532 Å (HSEH1PBE) as consistent with previously reported values [34,35]. In Table 2, the C11eC12 bond length is shorter than other methyl group CeC bonds due to presence of delocalized p-electronic system throughout the pyrazole ring. The optimized molecular geometry obtained at HSEH1PBE/6-311G(d,p) level is presented in Fig. 2b. To make a comparison between the X-ray and HSEH1PBE results, we present linear correlation coefficients (R2) for linear regression analysis of theoretical and experimental bond lengths and angles. R2 value is found to be 0.99202 and 0.99292 for bond lengths and bond angles, respectively. As one can easily see from above cited correlation coefficients, there is a perfect correlation between the experimental and theoretical geometric results. The small differences are due to the fact that experimental results belong to solid phase, while theoretical calculations belong to gas phase of isolated molecule. A perspective view of hydrogen bonded network for BPTBMPA crystal is presented in Fig. 3 and, the hydrogen bond lengths and bond angles are given in Table 3. There are four types of hydrogen bonds in the crystal structure of the BPTBMPA. All of them can be considered weak hydrogen bonding interaction. 4.2. Vibrational analysis The FT-IR spectrum has been recorded at the region of 4000e600 cm1, and the observed spectrum is presented in Fig. 4 as compared with calculated IR spectrum. The theoretical vibration frequencies have been calculated by using HSEH1PBE level and 6311G(d) basis set. Some of the experimental and theoretical vibration wavenumbers and their assignments have been presented in Table 4. Since DFT levels overestimate the vibration wavenumbers due to the electron correlation approximate treatment, the anharmonicity effect and basis set deficiency, etc., the calculated vibration wavenumbers are scaled down with 0.9614 [36]. 4.2.1. Amine group vibrations It is reported that primary amines gives peaks around 3300 cm1 which is responsible for NH stretching vibrations. The FT-IR spectrum for BPTBMPA gives peaks at 3453 and 3350 cm1, and these peaks are assigned as asymmetric and symmetric NH stretching vibration. These peaks are also calculated at 3514 and 3425 cm1, respectively. Obtained results are in good agreement with literature [37]. The in plane and out of plane bending vibrations of amine group are observed at 1616 and 1131 cm1, and calculated at 1603 and 1124 cm1, respectively.
Fig. 2. a) Ortep diagram of BPTBMPA with thermal ellipsoids at the 50% probability level, b) optimized molecular structure obtained at HSEH1PBE/6-311G(d,p) level.
4.2.2. Phenyl ring vibrations The aromatic CH stretching vibrations normally occur in the range of 3100e3000 cm1 [38] and these vibrations generally are not affected by the substitution of ring. In our study, phenyl ring CH stretching vibrations have been observed at 2973 cm1, and
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
92
Fig. 3. Crystal packing diagram.
Table 3 Hydrogen bond distances (Å) and angles ( ) for BPTBMPA. DdH
…
A
C10eH/N1 C6eH6…Br1i C10eH/Br1ii N1eH/N3iii
D-H
H …A
D…A
D-H…A
0.98 0.95 0.98 0.895(17)
2.58 3.05 3.11 2.39(2)
3.086(4) 3.947(3) 3.940(3) 3.179(3)
112.3 158.2 143.1 147.(2)
Symmetry codes: (i) -xþ2, -yþ1, -zþ2, (ii) -xþ1, yþ1/2, -zþ3/2, (iii) x, -yþ3/2, zþ1/2.
calculated at the region of 3098e3064 cm1. It is also reported that in plane CH bending vibrations occur in the range of 1300e1000 cm1, while out of plane ones occurs at the range of 1000e750 cm1 [39]. The in plane CH bending vibrations are observed at the range of 1306e1066 cm1, while out of plane CH bending are observed at 792 cm1. These vibrations are also
calculated at 1296e1059 and 810 cm1, respectively. As for the aromatic CC stretching vibrations, these vibrations are observed at 1591, 1364 and 1306 cm1, and calculated at 1592, 1347 and 1296 cm1. Both of the experimental and theoretical vibration spectra are consistent with previously reported studies [40,41].
4.2.3. Pyrazole ring vibrations Since the pyrazole ring has several bands having variable intensities in the range of 1600e1000 cm1 due to ring stretching vibration, the assignments of these peaks are known as a very rough task [42,43]. We have assigned the pyrazole ring CC, CN and NN stretching vibrations with the aid of GaussView 05 program. The peaks observed at the range of 1616e1230 cm1 in FT-IR spectrum are originated from the CN stretching vibration. These peaks have been calculated at 1603e1226 cm1 by using HSEH1PBE level. The presence of pyrazole ring can be proved by NN vibration
Fig. 4. The comparison of FT-IR and theoretical IR spectra for BPTBMPA.
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O. Table 4 Experimental and theoretical characteristic vibration wavenumbers for BPTBMPA. Assignments
FT-IR
HSEH1PBE
n NH n NH n CH n CH3 n CC þ n CN þ b NH2 (pz) n CC (p) n CC þ n CN (pz) n CC þ n CN (pz) b CH3 b CH3 n CN (pz) n CC (phenyl) n CC þ b CH (p) n CC (t) n CN(pz) n NN (pz) b CH g NH2 b CH b CH g CH3 b CC g CH3 g CH g CC g CC
3453 3350 2973 2918 1616 1591 1552 1513 1468 1447 1383 1364 1306 1295 1230 1177 1149 1131 1103 1066 1023 953 859 792 711 639
3514 3425 3098-3064 3041-2928 1603 1592 1550 1510 1457 1437 1387 1374 1296 1281 1226 1162 1157 1124 1091 1059 1016 984 848 810 716 628
n: stretching, b: in plane bending, g: out of plane bending, pz: pyrazole ring, p: phenyl ring.
peak observed at 1177 cm1 and calculated at 1162 cm1. 4.2.4. Methyl group vibrations The vibrational peaks due to the asymmetric and symmetric methyl stretching modes have been usually observed at about 2965 and 2880 cm1, respectively [44]. The methyl stretching vibration for BPTBMPA has been observed at 2918 cm1 and this peak have been also calculated at the region of 3041e2928 cm1, as consistent with literature [45,46]. The CH3 in plane bending vibrations have been observed at 1468 and 1447 cm1, while out of plane bending vibrations have been measured at 1023 and 859 cm1. It can be seen in Table 4, the HSEH1PBE results are consistent with FT-IR results. 4.3.
1
H and
13
C NMR spectra
The isotropic chemical shifts are frequently used to predict and interpret the structure of large molecular systems. Additionally, the combined use of NMR and theoretical methods presents an opportunity to obtained more accurate results. 1H and 13C NMR spectra have been recorded in CDCl3 solvent and presented in Fig. 5a and Fig. 5b, respectively. After BPTBMPA was fully optimized in CDCl3 solvent, 1H and 13C NMR spectra have been calculated by using HSEH1PBE/6-311G(d,p) level. Obtained experimental and theoretical chemical shifts are presented in Table 5. The 1H NMR chemical shifts for phenyl ring, which are generally found at the range of 8.29e6.88 ppm [14,47], have been observed at the region of 7.53e7.13 ppm and calculated at the range of 7.71e7.51 ppm. The amine group protons give NMR peak at 3.64 ppm in Fig. 5a, and this peak has been calculated at 3.98 and 3.23 ppm. Among the methyl groups, the protons bonding to C11 atom give downfield regions due to the delocalized p-electrons around the phenyl ring. This methyl group gives peak at 2.18 ppm, while other methyl groups give peak at 1.66 ppm. This difference has been also supported by HSEH1PBE level calculations. It is well known that methyl group carbons give peaks at the region of 200e100 ppm [48]. In this study, the methyl carbon NMR peaks are
93
observed at the region of 133.1e119.9 ppm, as consistent with calculated ones. From Table 5, the chemical shifts for C4 and C1 is found to be higher than the other phenyl carbon atoms due to the Cl atom. Among the carbon atoms, C14 and C12 give the highest NMR chemical shifts due to the electronegativity property of N atom. These peaks have been calculated at 148.2 and 146.0 ppm, respectively. The methyl group carbons chemical shift peaks have been observed at the range of 29.6e13.3 ppm, and calculated at the range of 32.4e15.6 ppm. All of the obtained 1H and 13C NMR chemical shifts have been found as consistent with literature [49,50]. 4.4. UVevis absorption and FMOs analysis The electronic absorption spectrum of BPTBMPA has been measured in dichloromethane solution and shown in Fig. 6. Time dependent DFT (TD-DFT) calculations have been also performed to obtain theoretical electronic spectrum based on the optimized molecular structure in dichloromethane solvent. The experimental and theoretical electronic absorption wavelengths, oscillator strengths and important contributions have been presented in Table 6. It is clear in Fig. 6, there are three electronic absorption observed at 210, 225 and 275 nm, respectively, which are in the ultraviolet region. These absorptions peaks have been also calculated by using HSEH1PBE level and found to be 255, 288 and 290 nm, respectively. All of these peaks are assigned as the combination of n / p* and p / p* transitions. The peak calculated at 255 nm has been originated from the combination of H / Lþ2 (67%), H-1 / Lþ2(14) and H-2 / Lþ2(10). The electronic absorption peak observed at 275 nm and calculated at 290 nm has been originated by the combination of HOMO / LUMO(57%) and HOMO / LUMOþ1 (43%). The HOMO are located around pyrazole ring (52%), amine group (22%) and phenyl ring (18%), while LUMO are located around phenyl ring (79%), pyrazole ring (11%). Additionally, LUMOþ1 is located around phenyl ring (93%) and amine group (3%). In this regard, it is clear from the above mentioned data, the peak at 275 nm is originated from the charge transfer between p(pyrazole)/n(amine) / p*(phenyl)/p*(pyrazole) with the 57% contribution and p(pyrazole)/n(amine) / p*(phenyl) with the 43% contribution. Therefore, the nature of all electronic absorption peaks has been designated in Table 6. The highest occupied molecular orbital and lowest unoccupied molecular orbitals are the main orbitals taking part in chemical reactions. HOMO energy characterizes the ability of electron giving, while LUMO energy characterizes the ability of electron accepting. Some of the occupied and unoccupied MOs which are active in electronic absorptions are presented in Fig. 7. The HOMO and LUMO energies have been found to be 5.4039 and 0.9080 eV, respectively. The band gap between the HOMO and LUMO is also found to be 4.4959 eV, demonstrating that charge transfer occurs in BPTBMPA. The electronegativity (c), chemical hardness (h), chemical potential (m) and electrophilicity (u) which are important parameters in quantum chemistry used to predict reactivity can be obtained by using HOMO and LUMO energies. h is known as an indicator of the resistance of a molecular system to change its electronic configuration [51]. It is also used as an indicator of the chemical reactivity and stability of systems. m reflects the tendency of donating of electrons from the equilibrium system [51e53]; it is therefore related to the electronic charge rearrangement associated to any chemical process. u can presents information comparing two molecules in which one is an electrophile (or nucleophile) and this is indicated by a higher (or lower) u. Having in mind all of the above mentioned facts, c, h, m and u parameters have been found to be 3.1559, 2.2479, 3.1559 and 2.2153 eV. The small h value is an indicator of the dominance of electron donating group in molecular
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€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
Fig. 5. a) 1H NMR b)
13
C NMR chemical shifts for BPTBMPA.
system. m is known by the an opposite behavior to that of h, so the high value of this parameter is an also indicator of electron donor groups. 4.5. NBO analysis Natural bond orbital (NBO) analysis presents an efficient method in order to study intra and intermolecular bonding and interaction among bonds, stabilization energy and charge transfer in molecular system by using second-order perturbation theory [54,55]. NBO analysis is performed by examining all possible interactions between donor (occupied) NBOs and acceptor (unoccupied) NBOs. The hyperconjugative interaction energy was deduced from the second-order perturbation approach [56]. In NBO analysis, large E(2) values demonstrate the intensive interaction between electron-donors and electron-acceptors and greater the extent of conjugation of the whole system, the possible intensive interactions are given in Table 7. For each donor (i) and acceptor (j), the stabilization energy Eð2Þ associates with the delocalization i / j
is estimated as;
Eð2Þ ¼ DEij ¼ qi
Fði; jÞ2 εi εj
(1)
where qi is the donor orbital occupancy, εj and εi the diagonal elements and Fði; jÞ is the off diagonal NBO Fock matrix element. The intramolecular interactions are due to orbital overlap between bonding CeC, LP N, LP Br and antibonding p*(CeC) and p*(CeN) orbitals, and this leads to an intramolecular charge transfer (ICT) causing stabilization of the system. These interactions are observed as an increase in electron density (ED) in CeC and CeN antibonding orbital that weakens the respective bonds. The intramolecular hyperconjugative interaction of s (C1eC6) distributes to s* (C5eC6) and (C1eC2) leading to stabilization of 3.77 and 3.95 kcal/mol, respectively. This enhances further conjugation with antibonding orbitals of p* (C4eC5) and p* (C2eC3) which leads to strong delocalization of 16.09 and 19.11 kcal/mol, respectively. The
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O. Table 5 Experimental and theoretical 1H and13C chemical shifts for BPTBMPA. Atom
Experimental
HSEH1PBE
1
H H2 H6 H3 H5 NH H10 H9 H8 H11 13 C C14 C12 C4 C1 C2 C6 C3 C5 C13 C7 C8 C10 C9 C11
7.53 7.51 7.16 7.13 3.64 1.66 1.66 1.66 2.18
7.71 7.70 7.57 7.51 3.98e3.23 1.56e1.26 2.56e1.15 2.12e1.15 2.41e2.02
143.2 142.1 133.1 132.2 130.7 130.7 119.9 119.9 106.2 58.6 29.6 13.3 13.3 13.3
148.2 146.0 139.6 137.7 137.6 137.5 134.9 132.9 108.2 60.6 32.4 28.5 26.3 15.6
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CeC and CeN anti-bonding orbitals that weakens the respective bonds. The most important interaction has been observed as LP(1) N2 / s*(C12eC14) with the stabilization energy of 46.86 kcal/mol. These large hyperconjugative interaction energies are strong evidences to intramolecular charge transfer leading to improve NLO properties BPTBMPA.
4.6. Molecular electrostatic potential The molecular electrostatic potential (MEP) which is a plot of electrostatic potential mapped onto the constant electron density surface is a useful technique related to the total electron density, and it gives powerful evidences concerning reactive sites for electrophilic and nucleophilic reactions as well as hydrogen bonding interactions. In order to predict reactive sites, positive and negative potential regions and hydrogen bonding interactions, MEP surface has been simulated by using HSEH1PBE/6-311G(d,p) level, and presented in Fig 8. The negative regions represented by red and yellow colors are associated with electrophilic reactivity and positive regions represented by blue color are associated with nucleophilic reactivity. The color code of the map is in the range between 0.06071 (deepest blue) and 0.06071 (deepest red). From Fig. 8, the negative regions in BPTBMPA have been found around the pyrazole ring and Cl atom, while positive regions have been found around the amine group protons and methyl protons. From above results, we can tell the H atoms of amine group indicate the strongest attraction as well as pyrazole ring N atoms and Cl atoms indicate the strongest repulsion.
4.7. Nonlinear optics
Fig. 6. The comparison of experimental and theoretical UVeVis spectra for BPTBMPA.
strong intramolecular hyperconjugative interaction of LP(1) N2 / p*(C12eN3) which increases ED (0.39900 e) that weakens the respective bonds leads to stabilization of 25.56 kcal/mol. The other strong intramolecular hyperconjugative interaction of LP(1) N1 / p*(C12eC14) which increases ED (0.43977 e) that weakens the respective bonds leads to stabilization of 22.84 kcal/mol. These interactions are observed as an increase in electron density (ED) in
Nonlinear optical materials (NLO) have been gathered great attention in recent years due to their future potential applications in optical communication, optical computing, and dynamic image processing applications [57,58]. It is well known that one of the essential requirements for more active NLO properties is the higher values of molecular polarizability and hyperpolarizability. The NLO properties of p-conjugated systems can be enhanced by the substitution with electron donor and acceptor groups. BPTBMPA molecule has methyl and amine groups as well as Cl atom substituted to p-conjugated phenyl and pyrazine ring. Additionally, BPTBMPA molecule has considerable p-conjugated bridge between these functional groups. So, the dipole moment (m), polarizability (a0) and hyperpolarizability (b) for BPTBMPA, novel synthesized molecular system, have been calculated by using HSEH1PBE/6311G(d,p). The m, and Da for BPTBMPA have been found to be 3.462 Debye, 31.863 1024 esu and 21.439 1024 esu, respectively. Finally, the b parameter for BPTBMPA has been found to be 6.209 1030 esu, and this value is approximately 48 times bigger than that of the standard NLO material urea (0.13 1030 esu) [59]. The obtained parameters are also comparable with another NLO material pNA (14.39 1030 esu) [60,61].
Table 6 The experimental and theoretical electronic absorption wavelengths and important contributions for BPTBMPA. Experimental
HSEH1PBE
l (nm) (DCM)
l (nm) (DCM)
Osc. Strength
Important contributions
275 225 210
290 288 255
0.2185 0.1819 0.0018
HOMO / LUMO(57%) HOMO / LUMOþ1(54%) HOMO / LUMOþ2 (67%)
HOMO / LUMOþ1 (43%) HOMO / LUMO(44%) HOMO-1 / LUMOþ2(14)
HOMO-2 / LUMOþ2(10)
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Fig. 7. The pictures of occupied and unoccupied MOs which are active in the electronic transitions obtained at HSEH1PBE/6-311G(d,p) level.
Table 7 Second order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra-molecular bonds of BPTBMPA. Type
Donor (i)
ED (i) ea
Type
Acceptor (j)
ED (j)a e
E(2) (kcal/mol)b
s s s s s p p p p p p p s p
C5eC6 C5eC6 C5eC6 C1eC6 C1eC6 C1eC6 C1eC6 C5eC4 C5eC4 C2eC3 C2eC3 C13eC14 C12eC13 C12eN3 N3 N2 N2 N1 Br1
1.96812 1.96812 1.96812 1.97916 1.97916 1.68590 1.68590 1.64123 1.64123 1.67522 1.67522 1.74075 1.96191 1.89888 1.93830 1.57529 1.57529 1.86869 1.93611
s* s* s* s* s* p* p* p* p* p* p* p* s* p* s* s* p* p* p*
C1eC6 C4eC5 C1eBr1 C5eC6 C1eC2 C4eC5 C2eC3 C1eC6 C1eC2 C1eC6 C5eC4 C12eN3 C14eN1 C13eC14 C14eN2 C12eC11 C12eN3 C13eC14 C1eC6
0.02880 0.02744 0.03647 0.01838 0.02884 0.37487 0.31339 0.39746 0.02884 0.39746 0.37487 0.39900 0.02112 0.43977 0.04438 0.01969 0.39900 0.43977 0.39746
4.58 3.74 5.56 3.77 3.95 16.09 19.11 22.23 17.95 18.86 18.96 30.05 7.31 10.35 7.31 46.86 25.56 22.84 9.81
LP(1) LP(1) LP(1) LP(1) LP(3) a b
ED: Electron density. E(2): Mean energy of hyperconjugative interaction.
spectrum show that there are three electronic absorption bands, and these bands are assigned n / p* and p / p* transitions. The important contributions to the electronic transitions have been designated. The UVeVis peak calculated at 290 nm have been originated from the combination of HOMO / LUMOþ1 (43%) and HOMO / LUMO (57%). The relatively small HOMO-LUMO energy gap and large hyperconjugative interaction energies (E(2)) are strong evidences intramolecular charge transfer leading to increase NLO properties of BPTBMPA. The reactive sites of BPTBMPA for electrophilic and nucleophilic attacks have been visualized on MEP surface. The NLO properties of BPTBMPA have been evaluated by the determining of polarizability and hyperpolarizability. It is demonstrated that this molecule can be used as an efficient NLO material. Acknowledgment The CCDC number 1412787 contain the supplementary crystallographic data (CIF) for this article. These data can be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: þ44-1223-336-033; e-mail: [email protected]. ac.uk or http://www.ccdc.cam.ac.uk). References
Fig. 8. Molecular electrostatic potential (MEP) surface for BPTBMPA obtained at HSEH1PBE/6-311G(d,p) level.
5. Conclusions A novel pyrazole derivate, 4-(4-bromophenyl)-1-tert-butyl-3methyl-1H-pyrazol-5-amine, has been synthesized for the first time. Its structural and spectroscopic properties have been examined by X-ray diffraction, FT-IR, NMR, UVeVis techniques as well as DFT calculations. Obtained results indicate that HSEH1PBE level can reproduce the experimental results. The simultaneously active CC, CN and NN peaks have been observed and calculated in IR spectra. All of the 1H and 13C NMR chemical shifts have been found in the expected region. The C atoms bounding to electronegative N atoms give down field regions. The theoretical and experimental UVeVis
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, molecular structure, spectral analysis and nonlinear optical studies on 4-(4-bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5amine: A combined experimental and DFT approach € lu b, Yusuf Atalay a, Omer Tamer a, Barıs¸ Seçkin Arslan b, Davut Avcı a, *, Mehmet Nebiog c Bünyemin Ços¸ut a b c
Sakarya University, Department of Physics, Arts and Sciences Faculty, 54187 Sakarya, Turkey Sakarya University, Department of Chemistry, Arts and Sciences Faculty, 54187 Sakarya, Turkey Gebze Technical University, Department of Chemistry, 41400 Gebze, Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 August 2015 Received in revised form 23 October 2015 Accepted 26 October 2015 Available online 29 October 2015
4-(4-bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5-amine (BPTBMPA) crystal was synthesized for the first time and its structural characterization was performed by X-ray diffraction method. The spectroscopic characterization was also performed by the applying of FT-IR, UVeVis, 1H and 13C NMR spectroscopies. In order to support experimental results, density functional theory calculations have been performed. All of the obtained theoretical results are in a perfect agreement with the experimental ones. The negative HOMO and LUMO energies demonstrated that the molecular structure of BPTBMPA is stable. The small energy gap between the HOMO and LUMO is an indicator of intramolecular charge transfer which is responsible for nonlinear optical properties. Natural bond orbital analysis also indicates the presence of molecular charge transfer within BPTBMPA. Obtained chemical hardness parameter demonstrates that BPTBMPA has considerable electron donor groups. Finally, it has been showed that BPTBMPA exhibits considerable nonlinear optical properties. © 2015 Elsevier B.V. All rights reserved.
Keywords: 4-(4-Bromophenyl)-1-tert-butyl-3-methyl1H-pyrazol-5-amine X-ray NMR FTIR DFT Nonlinear optics
1. Introduction Pyrazoles and its derivatives, a class of well-known nitrogen heterocycles, have attracted considerable interest in the pharmaceutical and agrochemical industries because of their diverse biological activities, such as, anti-inflammatory [1], antiviral [2], antimicrobial [3], anticonvulsant [4], antitumor [5], fungicidal activities [6] and antihistaminic [7]. As pyrazole derivatives rarely exist in nature, probably, due to the difficulty in the construction of NeN bond by living organisms, their availability particularly depends on the synthetic methods [8]. One of the most important derivatives of pyrazoles is 5-aminopyrazoles and their chemistry has been reviewed several times recently [9e12]. The most versatile method available for the synthesis of 5-aminopyrazoles involves the condensation of b-ketonitriles with hydrazines. Besides of the well-known biological activities, pyrazoles
* Corresponding author. E-mail address: [email protected] (D. Avcı). http://dx.doi.org/10.1016/j.molstruc.2015.10.084 0022-2860/© 2015 Elsevier B.V. All rights reserved.
derivatives substituted with electron donor and acceptor groups exhibit considerable nonlinear optical properties [13e15]. Up to now, a number of new organic crystals have been discovered with the aid of experimental and computational molecular engineering approaches and shown to have potential applications in nonlinear optics. But, in order to satisfy day to day increasing technological requirements, the search for new NLO materials has been still receiving great interest. It is well known that NLO properties of organic molecules depend on the intermolecular charge transfer [16e18]. At the same time, the molecular hydrogen bonding has been found to play an important role in adjusting NLO properties. Additionally, the substitution of conjugated p system with appropriate donor acceptor groups increase the asymmetric charge distribution in the ground state and excited state, and this leads to improve NLO properties [19,20]. So, 4-(4bromophenyl)-1-tert-butyl-3-methyl-1H-pyrazol-5-amine (BPTBMPA) molecule, which is an substituted pyrazole, has been considered as an interesting molecule due to the presence of pyrazole ring, electron donor NH2 and CH3 groups and Cl atom. Therefore, BPTBMPA may be exhibit considerable NLO properties.
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In this paper, we have synthesized BPTBMPA crystal for the first time and its crystal structure has been characterized by X-ray diffraction method. The spectroscopic properties of BPTBMPA have been evaluated by the applying of FT-IR, NMR and UVeVis spectroscopies as well as density functional theory (DFT) calculations. Additionally, natural bond orbital analysis and the investigations of NLO properties for BPTBMPA have been performed by DFT method. 2. Experimental details 2.1. Synthesis of 4-(4-bromophenyl)-1-tert-butyl-3-methyl-1Hpyrazol-5-amine To a solution of 2-(4-bromophenyl)-3-oxobutanenitrile 1 (2 mmol, 0.476 g) and tert-butylhydrazine hydrochloride (1.2 eq., 0.299 g) in toluene (10 mL) was added acetic acid (% 10 mol, 0.0115 mL) and the mixture was heated to reflux temperature for 5 h. The synthesis scheme for BPTBMPA was presented in Fig. 1. After completion of the reaction as monitored by TLC, the solvent was removed under reduced pressure. To this crude concentrate, water was added and extracted into ethyl acetate. The organic layer was dried over anhydrous sodium sulphate, concentrated under reduced pressure to give crude 2. It was crystallized from methanol and yielded 81% (colorless crystals, mp 161e162 C). 2.2. Instrumentation FT-IR spectrum for BPTBMPA was recorded on a PerkineElmer FT-IR spectrophotometer at the region of 4000e600 cm1. 1H and 13 C NMR spectra were measured on a Varian Infinity Plus spectrometer at 300 and 75 Hz, respectively. 1H and 13C chemical shifts are referenced to the internal deuterated solvent. The UVevis absorption spectrum was examined in the range 200e800 nm using a Shimadzu UV-2600 spectrophotometer in dichloromethane solvent. 2.3. X-ray crystal structure determination The solid-state structure of BPTBMPA has been confirmed by Xray diffraction analysis. Data have been obtained with Bruker APEX II QUAZAR three-circle diffractometer. Indexing was performed using APEX2 [21]. Data integration and reduction were carried out with SAINT [22]. Absorption correction was performed by multiscan method implemented in SADABS [23]. The Bruker SHELXTL [24] software package was used for structure solution and structure refinement. All non-hydrogen atoms were refined anisotropically using all reflections with I > 2s(I). Aromatic C-bound H atoms were positioned geometrically and refined using a riding mode. Crystallographic data and refinement details of the data collection for BPTBMPA are given in Table 1. The selected bond lengths and bond angles are given in Table 2. Final geometrical calculations were performed using PLATON software [25]. MERCURY software [26] was used for visualization of the cif files. The important conditions for the data collection and the structure refinement parameters of BPTBMPA are also given in Table 1.
Table 1 Crystal data and refinement parameters for BPTBMPA. CCDC Empirical Formula Formula weight (g.mol1) Temperature (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) a( ) b( ) g( ) Crystal size (mm) V (Å3) Z Density (g/cm3) m (mm1) F(000) q range for data collection ( ) h/k/l Reflections collected Independent reflections Absorption correction Data/restraints/parameters Goodness-of-fit on F2 (S) Final R indices [I > 2s(I)] R indices (all data) Largest diff. peak and hole (e.Å3)
C14H18BrN3 308.22 173 (2) 0.71073 monoclinic P21/c 5.9314(10) 20.050(3) 11.8114(16) 90 96.169(11) 90 0.345 0.109 0.107 1396.5(4) 4 1.446 2.930 632 2.03e26.73 7/6, 23/25, 14/14 12537 2964 [R(int) ¼ 0.0840] multi-scan 2964/2/173 1.038 R1 ¼ 0.0358, wR2 ¼ 0.0877 R1 ¼ 0.0499, wR2 ¼ 0.0936 0.437 and 0.757
Table 2 The experimental and theoretical bond lengths (Å) and angles ( ) for BPTBMPA. Bond lengths
X-ray
HSEH1PBE
Bond angles
X-ray
HSEH1PBE
Br1eC1 C1eC6 C1eC2 C2eC3 C3eC4 C4eC5 C4eC13 C5eC6 C7eN2 C7eC10 C7eC9 C7eC8 C11eC12 C12eN3 C12eC13 C13eC14 C14eN2 C14eN1 N2eN3 R2
1.909(3) 1.369(4) 1.378(4) 1.384(4) 1.394(4) 1.397(3) 1.474(3) 1.385(4) 1.485(3) 1.518(4) 1.521(4) 1.524(4) 1.490(4) 1.330(3) 1.404(4) 1.384(3) 1.348(3) 1.381(3) 1.381(3)
1.898 1.387 1.389 1.388 1.401 1.402 1.461 1.389 1.480 1.532 1.531 1.526 1.490 1.316 1.418 1.392 1.356 1.390 1.356 0.99202
C6eC1eC2 C6eC1eBr1 C1eC2eC3 C3eC4eC13 C1eC6eC5 N2eC7eC10 N2eC7eC9 C10eC7eC9 N2eC7eC8 N3eC12eC13 N3eC12eC11 C14eC13eC12 C14eC13eC4 C12eC13eC4 N2eC14eN1 N2eC14eC13 C14eN2eN3 C14eN2eC7 C12eN3eN2
121.7(2) 118.7(2) 118.7(3) 122.3(2) 118.9(2) 110.1(2) 108.0(2) 111.7(2) 108.6(2) 111.7(2) 120.0(2) 104.6(2) 126.7(2) 128.7(2) 123.9(2) 107.8(2) 110.9(2) 129.4(2) 105.0(2)
120.7 119.6 119.4 121.4 119.2 109.7 108.8 111.5 109.4 111.3 120.1 104.0 126.6 129.4 124.2 107.3 111.1 129.0 106.3 0.99292
3. Computational details All of the calculations for BPTBMPA have been performed by using Gaussian 09 Rev: D.01 program [27], and the output files have
Fig. 1. The synthesis scheme for BPTBMPA.
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
been visualized by means of GaussView 05 program [28]. The ground state geometry and IR spectrum have been obtained by using HSEH1PBE (The recommended version of the full HeydScuseria-Ernzerhof functional) [29,30] level of density functional theory (DFT) with 6-311G(d,p) basis set. BPTBMPA has been also optimized in chloroform in order to calculate 1H and 13C NMR chemical shifts. The GIAO approach [31,32] which is one of the most common approaches for calculating nuclear magnetic shielding tensors has been used to calculate NMR spectra. BPTBMPA has been optimized in dichloromethane, and the UVevis spectrum has been calculated in the same solvent. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, absorption wavelengths, oscillator strengths and molecular orbital contributions to the electronic transitions for BPTBMPA have been calculated with the time dependent DFT (TD-DFT) method starting from the ground-state geometry optimized in the dichloromethane solvent. Natural bond orbital (NBO) calculation has been performed to understand various second order interaction between the filled orbital of one subsystem and vacant orbital of another subsystem which is measure of the molecular delocalization or hyperconjugation using NBO 3.1 program [33]. The NLO properties of BPTBMPA have been investigated by the determining of polarizability (a) and first order hyperpolarizability (b). 4. Results and discussion 4.1. Description of molecular structure The BPTBMPA crystal, an ORTEP 3 diagram (50% probability) with the atom labeling for synthesized crystal is shown in Fig. 2a, crystallizes in P21/c space group. The BPTBMPA crystal belongs to monoclinic system with the following cell dimensions: a ¼ 5.9314(10) Å, b ¼ 20.050(3) Å, c ¼ 11.8114(16) Å,
91
b ¼ 96.169(11) , Z ¼ 4 (Table 1). The experimental bond lengths and selected bond angles for BPTBMPA crystal are given in Table 2, as compared with theoretical ones obtained at HSEH1PBE level. The molecular structure of BPTBMPA contains pyrazole and pyridine rings, and these rings are planar with a maximum deviation of 0.9(3) and 1.4(4) . The CeC bond lengths in the phenyl rings are observed in the range of 1.369(4)e1.397(3) Å (XRD) and calculated in the range of 1.387e1.402 Å (HSEH1PBE). The bond lengths are consistent with previously phenyl ring-containing studies [34]. The C12eN3 and C14eN2 bonds have double bond character with the bond lengths of 1.330(3) and 1.348(3) Å, while other bonds in pyrazole ring (C12eC13, C13eC14 and N2eN3) have a single bond character with the bond lengths of 1.404(4), 1.384(3) and 1.381(3) Å, respectively. The methyl group CeC bond lengths are in the range of 1.490(4)e1.524(4) Å (XRD) and 1.490e1.532 Å (HSEH1PBE) as consistent with previously reported values [34,35]. In Table 2, the C11eC12 bond length is shorter than other methyl group CeC bonds due to presence of delocalized p-electronic system throughout the pyrazole ring. The optimized molecular geometry obtained at HSEH1PBE/6-311G(d,p) level is presented in Fig. 2b. To make a comparison between the X-ray and HSEH1PBE results, we present linear correlation coefficients (R2) for linear regression analysis of theoretical and experimental bond lengths and angles. R2 value is found to be 0.99202 and 0.99292 for bond lengths and bond angles, respectively. As one can easily see from above cited correlation coefficients, there is a perfect correlation between the experimental and theoretical geometric results. The small differences are due to the fact that experimental results belong to solid phase, while theoretical calculations belong to gas phase of isolated molecule. A perspective view of hydrogen bonded network for BPTBMPA crystal is presented in Fig. 3 and, the hydrogen bond lengths and bond angles are given in Table 3. There are four types of hydrogen bonds in the crystal structure of the BPTBMPA. All of them can be considered weak hydrogen bonding interaction. 4.2. Vibrational analysis The FT-IR spectrum has been recorded at the region of 4000e600 cm1, and the observed spectrum is presented in Fig. 4 as compared with calculated IR spectrum. The theoretical vibration frequencies have been calculated by using HSEH1PBE level and 6311G(d) basis set. Some of the experimental and theoretical vibration wavenumbers and their assignments have been presented in Table 4. Since DFT levels overestimate the vibration wavenumbers due to the electron correlation approximate treatment, the anharmonicity effect and basis set deficiency, etc., the calculated vibration wavenumbers are scaled down with 0.9614 [36]. 4.2.1. Amine group vibrations It is reported that primary amines gives peaks around 3300 cm1 which is responsible for NH stretching vibrations. The FT-IR spectrum for BPTBMPA gives peaks at 3453 and 3350 cm1, and these peaks are assigned as asymmetric and symmetric NH stretching vibration. These peaks are also calculated at 3514 and 3425 cm1, respectively. Obtained results are in good agreement with literature [37]. The in plane and out of plane bending vibrations of amine group are observed at 1616 and 1131 cm1, and calculated at 1603 and 1124 cm1, respectively.
Fig. 2. a) Ortep diagram of BPTBMPA with thermal ellipsoids at the 50% probability level, b) optimized molecular structure obtained at HSEH1PBE/6-311G(d,p) level.
4.2.2. Phenyl ring vibrations The aromatic CH stretching vibrations normally occur in the range of 3100e3000 cm1 [38] and these vibrations generally are not affected by the substitution of ring. In our study, phenyl ring CH stretching vibrations have been observed at 2973 cm1, and
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
92
Fig. 3. Crystal packing diagram.
Table 3 Hydrogen bond distances (Å) and angles ( ) for BPTBMPA. DdH
…
A
C10eH/N1 C6eH6…Br1i C10eH/Br1ii N1eH/N3iii
D-H
H …A
D…A
D-H…A
0.98 0.95 0.98 0.895(17)
2.58 3.05 3.11 2.39(2)
3.086(4) 3.947(3) 3.940(3) 3.179(3)
112.3 158.2 143.1 147.(2)
Symmetry codes: (i) -xþ2, -yþ1, -zþ2, (ii) -xþ1, yþ1/2, -zþ3/2, (iii) x, -yþ3/2, zþ1/2.
calculated at the region of 3098e3064 cm1. It is also reported that in plane CH bending vibrations occur in the range of 1300e1000 cm1, while out of plane ones occurs at the range of 1000e750 cm1 [39]. The in plane CH bending vibrations are observed at the range of 1306e1066 cm1, while out of plane CH bending are observed at 792 cm1. These vibrations are also
calculated at 1296e1059 and 810 cm1, respectively. As for the aromatic CC stretching vibrations, these vibrations are observed at 1591, 1364 and 1306 cm1, and calculated at 1592, 1347 and 1296 cm1. Both of the experimental and theoretical vibration spectra are consistent with previously reported studies [40,41].
4.2.3. Pyrazole ring vibrations Since the pyrazole ring has several bands having variable intensities in the range of 1600e1000 cm1 due to ring stretching vibration, the assignments of these peaks are known as a very rough task [42,43]. We have assigned the pyrazole ring CC, CN and NN stretching vibrations with the aid of GaussView 05 program. The peaks observed at the range of 1616e1230 cm1 in FT-IR spectrum are originated from the CN stretching vibration. These peaks have been calculated at 1603e1226 cm1 by using HSEH1PBE level. The presence of pyrazole ring can be proved by NN vibration
Fig. 4. The comparison of FT-IR and theoretical IR spectra for BPTBMPA.
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O. Table 4 Experimental and theoretical characteristic vibration wavenumbers for BPTBMPA. Assignments
FT-IR
HSEH1PBE
n NH n NH n CH n CH3 n CC þ n CN þ b NH2 (pz) n CC (p) n CC þ n CN (pz) n CC þ n CN (pz) b CH3 b CH3 n CN (pz) n CC (phenyl) n CC þ b CH (p) n CC (t) n CN(pz) n NN (pz) b CH g NH2 b CH b CH g CH3 b CC g CH3 g CH g CC g CC
3453 3350 2973 2918 1616 1591 1552 1513 1468 1447 1383 1364 1306 1295 1230 1177 1149 1131 1103 1066 1023 953 859 792 711 639
3514 3425 3098-3064 3041-2928 1603 1592 1550 1510 1457 1437 1387 1374 1296 1281 1226 1162 1157 1124 1091 1059 1016 984 848 810 716 628
n: stretching, b: in plane bending, g: out of plane bending, pz: pyrazole ring, p: phenyl ring.
peak observed at 1177 cm1 and calculated at 1162 cm1. 4.2.4. Methyl group vibrations The vibrational peaks due to the asymmetric and symmetric methyl stretching modes have been usually observed at about 2965 and 2880 cm1, respectively [44]. The methyl stretching vibration for BPTBMPA has been observed at 2918 cm1 and this peak have been also calculated at the region of 3041e2928 cm1, as consistent with literature [45,46]. The CH3 in plane bending vibrations have been observed at 1468 and 1447 cm1, while out of plane bending vibrations have been measured at 1023 and 859 cm1. It can be seen in Table 4, the HSEH1PBE results are consistent with FT-IR results. 4.3.
1
H and
13
C NMR spectra
The isotropic chemical shifts are frequently used to predict and interpret the structure of large molecular systems. Additionally, the combined use of NMR and theoretical methods presents an opportunity to obtained more accurate results. 1H and 13C NMR spectra have been recorded in CDCl3 solvent and presented in Fig. 5a and Fig. 5b, respectively. After BPTBMPA was fully optimized in CDCl3 solvent, 1H and 13C NMR spectra have been calculated by using HSEH1PBE/6-311G(d,p) level. Obtained experimental and theoretical chemical shifts are presented in Table 5. The 1H NMR chemical shifts for phenyl ring, which are generally found at the range of 8.29e6.88 ppm [14,47], have been observed at the region of 7.53e7.13 ppm and calculated at the range of 7.71e7.51 ppm. The amine group protons give NMR peak at 3.64 ppm in Fig. 5a, and this peak has been calculated at 3.98 and 3.23 ppm. Among the methyl groups, the protons bonding to C11 atom give downfield regions due to the delocalized p-electrons around the phenyl ring. This methyl group gives peak at 2.18 ppm, while other methyl groups give peak at 1.66 ppm. This difference has been also supported by HSEH1PBE level calculations. It is well known that methyl group carbons give peaks at the region of 200e100 ppm [48]. In this study, the methyl carbon NMR peaks are
93
observed at the region of 133.1e119.9 ppm, as consistent with calculated ones. From Table 5, the chemical shifts for C4 and C1 is found to be higher than the other phenyl carbon atoms due to the Cl atom. Among the carbon atoms, C14 and C12 give the highest NMR chemical shifts due to the electronegativity property of N atom. These peaks have been calculated at 148.2 and 146.0 ppm, respectively. The methyl group carbons chemical shift peaks have been observed at the range of 29.6e13.3 ppm, and calculated at the range of 32.4e15.6 ppm. All of the obtained 1H and 13C NMR chemical shifts have been found as consistent with literature [49,50]. 4.4. UVevis absorption and FMOs analysis The electronic absorption spectrum of BPTBMPA has been measured in dichloromethane solution and shown in Fig. 6. Time dependent DFT (TD-DFT) calculations have been also performed to obtain theoretical electronic spectrum based on the optimized molecular structure in dichloromethane solvent. The experimental and theoretical electronic absorption wavelengths, oscillator strengths and important contributions have been presented in Table 6. It is clear in Fig. 6, there are three electronic absorption observed at 210, 225 and 275 nm, respectively, which are in the ultraviolet region. These absorptions peaks have been also calculated by using HSEH1PBE level and found to be 255, 288 and 290 nm, respectively. All of these peaks are assigned as the combination of n / p* and p / p* transitions. The peak calculated at 255 nm has been originated from the combination of H / Lþ2 (67%), H-1 / Lþ2(14) and H-2 / Lþ2(10). The electronic absorption peak observed at 275 nm and calculated at 290 nm has been originated by the combination of HOMO / LUMO(57%) and HOMO / LUMOþ1 (43%). The HOMO are located around pyrazole ring (52%), amine group (22%) and phenyl ring (18%), while LUMO are located around phenyl ring (79%), pyrazole ring (11%). Additionally, LUMOþ1 is located around phenyl ring (93%) and amine group (3%). In this regard, it is clear from the above mentioned data, the peak at 275 nm is originated from the charge transfer between p(pyrazole)/n(amine) / p*(phenyl)/p*(pyrazole) with the 57% contribution and p(pyrazole)/n(amine) / p*(phenyl) with the 43% contribution. Therefore, the nature of all electronic absorption peaks has been designated in Table 6. The highest occupied molecular orbital and lowest unoccupied molecular orbitals are the main orbitals taking part in chemical reactions. HOMO energy characterizes the ability of electron giving, while LUMO energy characterizes the ability of electron accepting. Some of the occupied and unoccupied MOs which are active in electronic absorptions are presented in Fig. 7. The HOMO and LUMO energies have been found to be 5.4039 and 0.9080 eV, respectively. The band gap between the HOMO and LUMO is also found to be 4.4959 eV, demonstrating that charge transfer occurs in BPTBMPA. The electronegativity (c), chemical hardness (h), chemical potential (m) and electrophilicity (u) which are important parameters in quantum chemistry used to predict reactivity can be obtained by using HOMO and LUMO energies. h is known as an indicator of the resistance of a molecular system to change its electronic configuration [51]. It is also used as an indicator of the chemical reactivity and stability of systems. m reflects the tendency of donating of electrons from the equilibrium system [51e53]; it is therefore related to the electronic charge rearrangement associated to any chemical process. u can presents information comparing two molecules in which one is an electrophile (or nucleophile) and this is indicated by a higher (or lower) u. Having in mind all of the above mentioned facts, c, h, m and u parameters have been found to be 3.1559, 2.2479, 3.1559 and 2.2153 eV. The small h value is an indicator of the dominance of electron donating group in molecular
94
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
Fig. 5. a) 1H NMR b)
13
C NMR chemical shifts for BPTBMPA.
system. m is known by the an opposite behavior to that of h, so the high value of this parameter is an also indicator of electron donor groups. 4.5. NBO analysis Natural bond orbital (NBO) analysis presents an efficient method in order to study intra and intermolecular bonding and interaction among bonds, stabilization energy and charge transfer in molecular system by using second-order perturbation theory [54,55]. NBO analysis is performed by examining all possible interactions between donor (occupied) NBOs and acceptor (unoccupied) NBOs. The hyperconjugative interaction energy was deduced from the second-order perturbation approach [56]. In NBO analysis, large E(2) values demonstrate the intensive interaction between electron-donors and electron-acceptors and greater the extent of conjugation of the whole system, the possible intensive interactions are given in Table 7. For each donor (i) and acceptor (j), the stabilization energy Eð2Þ associates with the delocalization i / j
is estimated as;
Eð2Þ ¼ DEij ¼ qi
Fði; jÞ2 εi εj
(1)
where qi is the donor orbital occupancy, εj and εi the diagonal elements and Fði; jÞ is the off diagonal NBO Fock matrix element. The intramolecular interactions are due to orbital overlap between bonding CeC, LP N, LP Br and antibonding p*(CeC) and p*(CeN) orbitals, and this leads to an intramolecular charge transfer (ICT) causing stabilization of the system. These interactions are observed as an increase in electron density (ED) in CeC and CeN antibonding orbital that weakens the respective bonds. The intramolecular hyperconjugative interaction of s (C1eC6) distributes to s* (C5eC6) and (C1eC2) leading to stabilization of 3.77 and 3.95 kcal/mol, respectively. This enhances further conjugation with antibonding orbitals of p* (C4eC5) and p* (C2eC3) which leads to strong delocalization of 16.09 and 19.11 kcal/mol, respectively. The
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O. Table 5 Experimental and theoretical 1H and13C chemical shifts for BPTBMPA. Atom
Experimental
HSEH1PBE
1
H H2 H6 H3 H5 NH H10 H9 H8 H11 13 C C14 C12 C4 C1 C2 C6 C3 C5 C13 C7 C8 C10 C9 C11
7.53 7.51 7.16 7.13 3.64 1.66 1.66 1.66 2.18
7.71 7.70 7.57 7.51 3.98e3.23 1.56e1.26 2.56e1.15 2.12e1.15 2.41e2.02
143.2 142.1 133.1 132.2 130.7 130.7 119.9 119.9 106.2 58.6 29.6 13.3 13.3 13.3
148.2 146.0 139.6 137.7 137.6 137.5 134.9 132.9 108.2 60.6 32.4 28.5 26.3 15.6
95
CeC and CeN anti-bonding orbitals that weakens the respective bonds. The most important interaction has been observed as LP(1) N2 / s*(C12eC14) with the stabilization energy of 46.86 kcal/mol. These large hyperconjugative interaction energies are strong evidences to intramolecular charge transfer leading to improve NLO properties BPTBMPA.
4.6. Molecular electrostatic potential The molecular electrostatic potential (MEP) which is a plot of electrostatic potential mapped onto the constant electron density surface is a useful technique related to the total electron density, and it gives powerful evidences concerning reactive sites for electrophilic and nucleophilic reactions as well as hydrogen bonding interactions. In order to predict reactive sites, positive and negative potential regions and hydrogen bonding interactions, MEP surface has been simulated by using HSEH1PBE/6-311G(d,p) level, and presented in Fig 8. The negative regions represented by red and yellow colors are associated with electrophilic reactivity and positive regions represented by blue color are associated with nucleophilic reactivity. The color code of the map is in the range between 0.06071 (deepest blue) and 0.06071 (deepest red). From Fig. 8, the negative regions in BPTBMPA have been found around the pyrazole ring and Cl atom, while positive regions have been found around the amine group protons and methyl protons. From above results, we can tell the H atoms of amine group indicate the strongest attraction as well as pyrazole ring N atoms and Cl atoms indicate the strongest repulsion.
4.7. Nonlinear optics
Fig. 6. The comparison of experimental and theoretical UVeVis spectra for BPTBMPA.
strong intramolecular hyperconjugative interaction of LP(1) N2 / p*(C12eN3) which increases ED (0.39900 e) that weakens the respective bonds leads to stabilization of 25.56 kcal/mol. The other strong intramolecular hyperconjugative interaction of LP(1) N1 / p*(C12eC14) which increases ED (0.43977 e) that weakens the respective bonds leads to stabilization of 22.84 kcal/mol. These interactions are observed as an increase in electron density (ED) in
Nonlinear optical materials (NLO) have been gathered great attention in recent years due to their future potential applications in optical communication, optical computing, and dynamic image processing applications [57,58]. It is well known that one of the essential requirements for more active NLO properties is the higher values of molecular polarizability and hyperpolarizability. The NLO properties of p-conjugated systems can be enhanced by the substitution with electron donor and acceptor groups. BPTBMPA molecule has methyl and amine groups as well as Cl atom substituted to p-conjugated phenyl and pyrazine ring. Additionally, BPTBMPA molecule has considerable p-conjugated bridge between these functional groups. So, the dipole moment (m), polarizability (a0) and hyperpolarizability (b) for BPTBMPA, novel synthesized molecular system, have been calculated by using HSEH1PBE/6311G(d,p). The m, and Da for BPTBMPA have been found to be 3.462 Debye, 31.863 1024 esu and 21.439 1024 esu, respectively. Finally, the b parameter for BPTBMPA has been found to be 6.209 1030 esu, and this value is approximately 48 times bigger than that of the standard NLO material urea (0.13 1030 esu) [59]. The obtained parameters are also comparable with another NLO material pNA (14.39 1030 esu) [60,61].
Table 6 The experimental and theoretical electronic absorption wavelengths and important contributions for BPTBMPA. Experimental
HSEH1PBE
l (nm) (DCM)
l (nm) (DCM)
Osc. Strength
Important contributions
275 225 210
290 288 255
0.2185 0.1819 0.0018
HOMO / LUMO(57%) HOMO / LUMOþ1(54%) HOMO / LUMOþ2 (67%)
HOMO / LUMOþ1 (43%) HOMO / LUMO(44%) HOMO-1 / LUMOþ2(14)
HOMO-2 / LUMOþ2(10)
€ Tamer et al. / Journal of Molecular Structure 1106 (2016) 89e97 O.
96
Fig. 7. The pictures of occupied and unoccupied MOs which are active in the electronic transitions obtained at HSEH1PBE/6-311G(d,p) level.
Table 7 Second order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra-molecular bonds of BPTBMPA. Type
Donor (i)
ED (i) ea
Type
Acceptor (j)
ED (j)a e
E(2) (kcal/mol)b
s s s s s p p p p p p p s p
C5eC6 C5eC6 C5eC6 C1eC6 C1eC6 C1eC6 C1eC6 C5eC4 C5eC4 C2eC3 C2eC3 C13eC14 C12eC13 C12eN3 N3 N2 N2 N1 Br1
1.96812 1.96812 1.96812 1.97916 1.97916 1.68590 1.68590 1.64123 1.64123 1.67522 1.67522 1.74075 1.96191 1.89888 1.93830 1.57529 1.57529 1.86869 1.93611
s* s* s* s* s* p* p* p* p* p* p* p* s* p* s* s* p* p* p*
C1eC6 C4eC5 C1eBr1 C5eC6 C1eC2 C4eC5 C2eC3 C1eC6 C1eC2 C1eC6 C5eC4 C12eN3 C14eN1 C13eC14 C14eN2 C12eC11 C12eN3 C13eC14 C1eC6
0.02880 0.02744 0.03647 0.01838 0.02884 0.37487 0.31339 0.39746 0.02884 0.39746 0.37487 0.39900 0.02112 0.43977 0.04438 0.01969 0.39900 0.43977 0.39746
4.58 3.74 5.56 3.77 3.95 16.09 19.11 22.23 17.95 18.86 18.96 30.05 7.31 10.35 7.31 46.86 25.56 22.84 9.81
LP(1) LP(1) LP(1) LP(1) LP(3) a b
ED: Electron density. E(2): Mean energy of hyperconjugative interaction.
spectrum show that there are three electronic absorption bands, and these bands are assigned n / p* and p / p* transitions. The important contributions to the electronic transitions have been designated. The UVeVis peak calculated at 290 nm have been originated from the combination of HOMO / LUMOþ1 (43%) and HOMO / LUMO (57%). The relatively small HOMO-LUMO energy gap and large hyperconjugative interaction energies (E(2)) are strong evidences intramolecular charge transfer leading to increase NLO properties of BPTBMPA. The reactive sites of BPTBMPA for electrophilic and nucleophilic attacks have been visualized on MEP surface. The NLO properties of BPTBMPA have been evaluated by the determining of polarizability and hyperpolarizability. It is demonstrated that this molecule can be used as an efficient NLO material. Acknowledgment The CCDC number 1412787 contain the supplementary crystallographic data (CIF) for this article. These data can be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: þ44-1223-336-033; e-mail: [email protected]. ac.uk or http://www.ccdc.cam.ac.uk). References
Fig. 8. Molecular electrostatic potential (MEP) surface for BPTBMPA obtained at HSEH1PBE/6-311G(d,p) level.
5. Conclusions A novel pyrazole derivate, 4-(4-bromophenyl)-1-tert-butyl-3methyl-1H-pyrazol-5-amine, has been synthesized for the first time. Its structural and spectroscopic properties have been examined by X-ray diffraction, FT-IR, NMR, UVeVis techniques as well as DFT calculations. Obtained results indicate that HSEH1PBE level can reproduce the experimental results. The simultaneously active CC, CN and NN peaks have been observed and calculated in IR spectra. All of the 1H and 13C NMR chemical shifts have been found in the expected region. The C atoms bounding to electronegative N atoms give down field regions. The theoretical and experimental UVeVis
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