научная статья по теме SYNTHESIS AND STRUCTURAL STUDY ON (1E,2E,1'E,2'E)-3,3'-BIS[(4- BROMOPHENYL)-3,3'-(4-METHY-1,2-PHENYLENE DIIMINE)] ACETALDEHYDE DIOXIME: A COMBINED EXPERIMENTAL AND THEORETICAL STUDY Физика

ОПТИКА И СПЕКТРОСКОПИЯ, 2015, том 118, № 6, с. 897-912

^^^^^^^^^^^^^^ СПЕКТРОСКОПИЯ

АТОМОВ И МОЛЕКУЛ

УДК 539.19

SYNTHESIS AND STRUCTURAL STUDY ON (1E,2E,1,E,2E)-3,3-BIS[(4-BROMOPHENYL)-3,3'-(4-METHY-1,2-PHENYLENE DIIMINE)] ACETALDEHYDE DIOXIME: A COMBINED EXPERIMENTAL AND THEORETICAL STUDY

© 2015 г. T. Topal*, H.H. Kart**, P. Tunay Ta§li**, and E. Karapinar*

* Department of Chemistry, Pamukkale University, Kinikli, 20017, Denizli, Turkey ** Department of Physics, Pamukkale University, Kinikli, 20017, Denizli, Turkey E-mail: tufantopal@hotmail.com, hkart@pau.edu.tr Received September 29, 2014

Tetradentate (1E,2E,1,E,2'E)-3,3,-bis[(4-bromophenyl)-3,3,-(4-methy-1,2-phenylene diimine)] acetalde-hyde dioxime which possess N4 donor sets derived from the condensation of isonitroso-p-bromoacetophe-none and 3,4-diaminotoluene are synthesized and characterized. The characterization of tetradentate Schiff base ligand has been deduced from LC-MS, FTIR, 13C and 1H NMR spectra and elemental analysis. Furthermore, the molecular geometry, infrared and NMR spectra of the title molecule in the ground state have been calculated by using the quantum chemical computational methods such as density functional theory (DFT) and ab initio Hartree-Fock (HF) methods with the 6-31G(d) and 6-311G(d) basis sets. The computed bond lengths and bond angles by using the both methods show the good agreement with each other. Moreover, the vibrational frequencies have been calculated and the scaled values have been compared with the experimental FTIR spectroscopic data. Assignments of the vibrational modes are made on the basis of potential energy distribution (PED) calculated from by using VEDA program. The correlations between the observed and calculated frequencies are in good agreement with each other as well as the correlation of the NMR data.

DOI: 10.7868/S0030403415060227

INTRODUCTION

Oximes represent a very significant group of li-gands in coordination chemistry [1—5]. The oximes li-gands can be used to synthesize symmetrical or un-symmetrical Schiff bases [5—8] that may then be made to undergo complexation with several metal ions. Or-ganometallic and coordination chemistries of oximes constitute an active research area with efforts in particular being directed toward unusual reactivity modes of oximes and their complexes [2, 3, 9, 10]. Schiff base metal complexes have been widely studied because they have industrial, antifungal, antibacterial, anticancer and herbicidal applications [11]. The condensation of primary amines with carbonyl compounds yields Schiff bases that are regarded as one of the most important group of chelators for facile preparations of new metal chelates. Schiff bases complexes and oxim-es represent important series of excellent chelating agents and they are widely used to synthesize mono-, di-, tri- or polynuclear transition metal complexes [12-15].

The experimental studies and theoretical calculations on the structural and vibrational properties of the title compound are insufficient in the literature. In order to apprehend and interpret the experimental

works, it is needed to be done the comprehensive theoretical studies of the molecular infrared and NMR properties of the title compound. The theoretical studies of the compounds provide ones to get the important information about the physical and chemical properties of them. An important tool for molecular identification is the vibrational spectroscopy. The presence of particular functional groups in the chemical molecules can be determined by analyzing the presence and intensity of various peaks in the infrared (IR) and Raman spectrums. However, it is not possible to assign the fundamental vibrational modes in the large molecules without theoretical calculations. Theoretical calculations can provide ones to assign the frequencies that can be used as fingerprint for the chemical compounds. The understanding of the relationship between the observed spectral features and the molecular structure can be difficult because of band assignments of vibrations [16]. The theoretical methods such as Hartree-Fock (HF) and Density Functional Theory (DFT) in the computational chemistry are important tools to predict the structural and vibra-tional properties of the molecules. These calculation methods are extensively used to study some physical and chemical properties of the materials and chemical compounds [17, 18]. The solution of the electronic

Schrödinger equation is essential to the applications of these methods to chemical problems in the ab initio calculations. The development of fast digital computers has opened the possibility of solving the electronic Schrödinger equation while utilizing approximations for interesting systems [19]. HF and DFT methods are extensively used to determine the molecular structures and vibrational spectra for small and large sized chemical molecules at cheap computational cost [20—31]. The computed harmonic vibrational frequencies are generally larger than the observed ones. This is due to the neglect of anharmonic effects in these methods used in computational chemistry. Additionally, errors are coming from the incomplete incorporation of electron correlation and finite basis sets [32]. In order to correct these errors some scaling factors are often applied to eliminate the systematic errors in the force constants and frequencies and provide better agreement with the observed ones. The geometry optimization of the molecule is an important factor for accurate determination of NMR chemical shifts [33] on the chemical shift calculations utilizing quantum chemistry methods.

The purpose of this work is to present the synthesis, experimental and theoretical characterization of the title compound. The molecular structure, vibrational and NMR spectra of the title compound are calculated by using the quantum chemistry methods based on DFT and HF levels with the basis set of 6-31G(d). Comparisons of the experimental and theoretical calculations can be very useful in making correct assignment and understanding the basic vibrational, NMR spectra and molecular structure relations.

To a solution of isonitroso-p-bromoacetophenone (6.84 g, 30 mmol) in absolute ethanol (30 mL), 3,4-diaminotoluene (1.83 g, 15 mmol) in absolute ethanol (15 mL) has been added under constant stirring. The mixture is stirred at room temperature for 2 h and monitored by thin layer chromatography (TLC) using ethyl acetate/n-hexane (1:5). After stripping off the excess solvent under reduced pressure, a yellow col-

EXPERIMENTAL

All remaining reagents have been purchased from Sigma, Fluka or Merck Company and have been used without further purification. In this study, we have measured the vibrational frequencies of title compound by using the FTIR spectroscopy. FT-IR spectrum is recorded by a Perkin Elmer FT-IR spectrometer Spectrum Two model (4000-400 cm-1). 13C NMR spectra has been recorded on a Bruker Ultra Shield Plus, Ultra long hold time 400MHz NMR spectrometer in the medium of Dimethyl Sulfoxide (DMSO).1H NMR spectra has been also recorded on a Bruker AVANCE 500 MHz 500MHz NMR spectrometer in the medium of DMSO. Elemental analyses (C, H, and N) have been measured by using a Thermo Finnigan Flash EA 1112 Model analyzer. Mass spectrum has been recorded by using Bruker-Daltonics micrOTOF-QII model spectrophotometer.

Synthesis

The preparation of isonitroso-p-bromoacetophe-none has been described in previous studies [34-37]. Route of synthesis of the title compound is given in Scheme 1. Preparation of (1E,2E,1' E,2'E)-3,3'-bis[(4-bromophenyl)-3,3'-(4-methy- 1,2-phenylene dii-mine)]acetaldehyde dioxime have been prepared from isonitroso-p-bromoacetophenone according to previous published methods [15, 38-41] (scheme 1).

ored ligand [H2L] solution is obtained. As the solution has cooled a powder product has precipitated. The solid is separated by filtration, washed with distilled water, cold ethanol and cold diethyl ether, and dried in air. Yellow compound; yield: 74%; (dec.):69°C, Anal. Calc. for C23H18Br2N4O2, C, 50.95; H, 3.35; N, 10.33; % Found: C, 50.65; H, 3.28; N, 10.30%; m/z(e.i.) = = 541.3 M+.

EtOH

jT^ -" H N

O N—OH I

/

H

Scheme 1. Synthesis of the title compound at room temperature.

13j 17

9Jyl S*

32 36 35

ist 31

2 3 45 25

10 5 30

Fig. 1. The optimized geometric structure of the title molecule with the atomic labelling of the atoms.

COMPUTATIONAL DETAILS

In recent years, DFT and HF methods have become powerful tools to investigate the molecular structure and vibrational spectra [42]. Hence, we have performed quantum mechanical calculations via the Gaussian 09 package by utilizing the DFT/B3LYP and HF methods to get information about the structural and vibrational properties of the title compound [43, 44]. Molecular structure of the title molecule is optimized to get the global minima of the compound at the levels of ab initio DFT/B3LYP and HF with the basis set of 6-31G(d)by considering Q symmetry.

The optimized geometric structure of the title compound is given in Fig. 1. The same basis set and methods are used to find the vibrational spectra by using the optimized structure. The optimized geometry for the title compound has not got any imaginary frequency modes. This means that there is a minimum energy configuration on the potential energy surface. In other words, the stability of the optimized geometries is verified by wavenumbers calculations giving no negative values for all the calculated wavenumbers. In order to predict the 1H and 13C NMR shielding constants by applying the Gauge Including Atomic Orbitals (GIAO) GIAO-DFT and GIAO-HF methods [44] in the medium of DMSO, the same calculation procedure can be used. The potential energy distribution (PED) is predicted by using the VEDA program [45] and the fundamental vibrational modes are characterized by their PEDs for the assignments of the experimental bands in details. PED calcula

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