научная статья по теме SYNTHESIS, SPECTROSCOPIC PROPERTIES AND DFT STUDY OF (E)-1-[(3-(TRIFLUOROMETHYL)PHENYLIMINO)METHYL]NAPHTHALEN-2-OLATE Физика

СПЕКТРОСКОПИЯ ^^^^^^^^^^

КОНДЕНСИРОВАННОГО СОСТОЯНИЯ

УДК 543.42

SYNTHESIS, SPECTROSCOPIC PROPERTIES AND DFT STUDY OF (^)-1-[(3-(TRIFLUOROMETHYL)PHENYLIMINO)METHYL]NAPHTHALEN-2-OLATE

© 2014 г. G. Alpaslan*, M. Macit**, A. Erdonmez***, and O. Büyükgüngor***

* Department of Medical Services and Techniques, Vocational High School of Health Services, Giresun University, 28200 Giresun, Turkey ** Department of Chemistry, Faculty of Arts & Science, Ondokuz May i s University, 55139 Samsun, Turkey *** Department of Physics, Faculty of Arts & Science, Ondokuz May is University, 55139 Samsun, Turkey

E-mail: galpaslan28@gmail.com Received August 7, 2013

The Schiff base (E)-1-[(3-(trifluoromethyl)phenylimino)methyl]naphthalen-2-olate was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde with 3-trifluoromethylaniline. The title compound has been characterized by FT-IR, UV-vis, and X-ray single-crystal techniques. The present X-ray investigation shows that the compound exists in the zwitterionic form. Molecular geometry of the compound in the ground state have been calculated using the density functional method (DFT) with 6-31G(d, p) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters. By using TD-DFT method electronic absorption spectra of the compound have been predicted and a good agreement with the TD-DFT method and experimental one is determined. In addition, DFT calculations of the compound, molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO-LUMO) and non-linear optical (NLO) properties were performed at B3LYP/6-31G(d, p).

DOI: 10.7868/S0030403414040023

INTRODUCTION

Schiff bases compounds have received special attention due to their interesting termochromism and/or photochromism [1, 2], biological properties [3, 4], as well as a variety of potential applications, e.g., for optical data storage [1, 2, 5], as nonlinear optical materials [6, 7]. Tautomerism and isomerism phenomena for these compounds are of particular chemical and theoretical interest in the context of their photochromic and thermochromic properties [2, 8]. Photo- and thermochromism are due to a change in the n-electron configuration induced by proton transfer [9, 10]. Such proton exchanging materials can be utilized for the design ofvarious molecular electronic devices [11]. o-Hydroxy Schiff bases display two possible tautomeric forms, the phenol-imine (OH) and the keto-amine (NH) forms. Depending on the tautomers, two types of intramolecular hydrogen bonds are observed in Schiff bases: O—H-N in phe-nol-imine [12, 13] and N—H-O in keto-amine [14, 15] tautomers. Another form of the Schiff base compounds is also known as zwitterion having an ionic intramolecular hydrogen bond (N+—H-O) and this form is rarely seen in the solid state [16, 17].

Investigation of structural stability of compounds by both experimental techniques and theoretical methods has been of great interest. Functional material design, theoretical modeling of drug design and so

on, has become possible as results of the development of the computational techniques. Many important properties such as molecular orbitals, electrostatic potentials, dipole moment, non-linear optical properties, vibrational frequencies can be predicted by various computational techniques [18—20].

In this study, we present results of a detailed investigation of the synthesis and structural characterization of (E)-1-[(3-(trifluoromethyl)phenylimino)me-thyl]-naphthalene-2-olate using IR, UV-vis, single-crystal X-ray diffraction and quantum chemical methods. The geometric parameters of the compound in the ground state were calculated using the DFT/B3LYP/6-31G(d, p) method. The properties of the structural geometry, molecular electrostatic potential (MEP), and non-linear optical (NLO) properties for the title compound at B3LYP/6-31G(d, p) level were studied.

EXPERIMENTAL AND COMPUTATIONAL METHOD

Synthesis of the Compound

(E)-1- [(3-(trifluoromethyl)phenylimino)meth-yl]naphthalene-2-olate was prepared by refluxing a mixture of a solution containing 2-hydroxy-l-naph-thaldehyde (17.2 mg, 0.1 mmol) in ethanol (20 mL) and a solution containing 3-(trifluoromethyl)aniline

Fig. 1. Synthesis of the title compound (C18H12F3NO).

(16.1 mg, 0.1 mmol) in ethanol (20 mL). The reaction mixture was stirred for 3 h under reflux. Single crystals of the title compound for X-ray analysis were obtained by slow evaporation of an ethanol solution. Yield 68%; m.p. 403-405 K (Fig. 1).

Instrumentation

The FT- IR spectrum of the title compound was recorded in the 4000—400 cm-1 region with a Shimadzu FTIR-8900 spectrophotometer using KBr pellet. Electronic absorption spectrum was measured on a Unicam UV-VIS spectrophotometer in EtOH solvent.

X-ray Single Crystal Structure Determination

A yellow crystal of the compound with dimensions of 0.46 x 0.30 x 0.18 mm was mounted on goniometer of a STOE IPDS II diffractometer. Measurements were performed at room temperature (296(2) K) using graphite monochromated Mo^a radiation (X = = 0.71073 A). The systematic absences and intensity symmetries indicated the monoclinic P21/c space group. A total of16963 reflections (1969 unique) within the 9 range of [2.3° < 9 < 28°] were collected in the scan mode. Cell parameters were determined by using X-AREA software [21]. Absorption correction (^ = = 0.12 mm-1) was obtained by the integration method via X-RED32 software [21]. The structure was solved by direct methods using SHELXS-97 [22]. The CF3 group showed rotational disorder. For atoms F1A, F2A, and F3A the site occupancy factor is 0.548 (6) and for F1B, F2B and F3B the site occupancy factor is 0.452 (6). The maximum peaks and deepest hole observed in the final Ap map were 0.51 and -0.42 eA3, respectively. The scattering factors were taken from SHELXL-97 [22]. The molecular graphics were done using Ortep-3 for Windows [23]. The data collection conditions and parameters of refinement process are listed in Table 1.

Crystallographic data for the structure reported in this article have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC 885814.

Computational Procedures

The molecular geometry is directly taken from the X-ray diffraction experimental results without any constraints. In the next step, the DFT calculations with a hybrid functional B3LYP (Becke's three parameter hybrid functional using the LYP correlation functional) at 6-31G(d, p) basis set by using Berny method [24, 25] were performed with the Gaussian 03W software package [26] and GaussView molecular visualization program [27]. The electronic absorption spectra were calculated using the time-dependent density functional theory (TD-DFT) method [28-31]. Also it is calculated in ethanol solution using the Polarizable Continuum Model (PCM) [32-35]. To investigate the reactive sites of the compound the molecular electrostatic potential was evaluated using the B3LYP/6-31G(d, p) method. The linear polarizability and first hyperpolarizability properties of the compound were obtained from molecular polarizabilities based on theoretical calculations.

RESULTS AND DISCUSSION

Structure Description of the Compound

The title compound crystallizes in the monoclinic, P21/c space group with Z = 4 in the unit cell. Figure 2 shows Ortep-3 diagram of the title compound with atom numbering scheme. The asymmetric unit in the crystal structure contains only one molecule. The C11-N1 [1.301(4) A] and C2-O1 [1.307(6) A] bonds of the compound are the most important indicators of the tautomeric type. While the C2-O1 bond is of a double bond for the keto-amine tautomer, this bond displays single bond character in phenol-imine tautomer. In addition, the C11-N1 bond is also a double bond in phenol-imine tautomer and of single bond length in keto-amine tautomer [36, 37]. However, these bond distances have intermediate values between single and double C-O (1.362 and 1.222 A, respectively) and C-N (1.339 and 1.279 A, respectively) bond distance [38]. The shortened C2-O1 bond and the slightly longer C11-N1 bond provide structural evidence for the zwitterionic tautomeric form of the title compound. In addition to zwitterionic forms of Schiff bases have an intramolecular ionic hydrogen bond (N+-H—O-), and their N+-H bond lengths are longer than those observed in neutral N-H bond

lengths (0.87 Á) [17, 39]. The N+-H bond distance [0.93 (11) Á] is comparable with that of zwitterions in the literature [39, 40].

It is known that Schiff bases may demonstrate pho-tochromism depending on the planarity or non-pla-narity, respectively [41]. The dihedral angle between the naphthalene plane (C1—C10) and the benzene plane (C12—C17) is 5.38(10)°.

The molecular structure is stabilized by N1+-H1 ••• O1- intramolecular hydrogen bond which generates an S(6) ring motif (Fig. 2) [42]. The sum of the Van der Waals radius of the N and O atoms [3.07 Á] is significantly longer than the intramolecular N1--O1 [2.574(5) Á] hydrogen bond length (Table 2) [43].

Optimized Structure

The optimized structure of the compound was calculated at the B3LYP/6-31G(d, p) level by DFT method, starting from the experimental structure. The selected bond lengths, bond angles and torsion angles are listed in Table 3 and compared with the experimental data of the compound. As shown in Table 3, most of the calculated bond lengths and the bond angles are slightly different from the experimental ones. The biggest deviation of the bond lengths is 0.047 Á at C2—O1 and the biggest deviation of the bond angles is 3.6° at C11—N1—C12. According to X-ray studies, the dihedral angle between the C1-C10 and C12-C17 rings is 5.38(10)°, while this angle has been calculated at 2.65° for B3LYP. In order to compare the theoretical results with the experimental values, root mean square error (RMSE) is used. The calculated R

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