СТЕКТРОСКОПИЯ АТОМОВ И МОЛЕКУЛ
CRYSTAL STRUCTURE, SPECTROSCOPIC PROPERTIES AND DENSITY FUNCTIONAL THEORY STUDY OF (Z)-1-[(2,4-DIMETHOXYPHENYLAMINO)METHYLENE]NAPHTHALEN-2(1H)-ONE
© 2014 г. Hakan Kargili*, Gokhan Alpaslan**, Mustafa Macit***, Ahmet Erdonmez*, and Orhan Büyükgüngor*
*Department of Physics, Faculty of Arts & Science, Ondokuz Mayis University, 55139 Samsun, Turkey ** 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 is University, 55139 Samsun, Turkey
E-mail: firstname.lastname@example.org Received May 15, 2013
The Schiff base (Z)-1-[(2,4-dimethoxyphenylamino)methylene]naphthalen-2(1H)-one was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde with 2,4-dimethoxyaniline. 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 keto-amine tautomeric form. Molecular geometry and vibrational frequencies of the compound in the ground state have been calculated using the density functional theory (DFT) with 6-311G(d,p) basis set and compared with the experimental data. The calculated results show that the optimized geometry is compatible with the crystal structure and the theoretical vibrational frequencies are in good agreement with the experimental values. Besides, molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO-LUMO) and non-linear optical (NLO) properties of the compound were investigated using the same theoretical calculations.
Schiff bases are used as starting materials in the synthesis of important drugs, such as antibiotics and antiallergic, antiphlogistic, and antitumor substance [1—3]. Schiff bases from 2-hydroxy-1-naphthalde-hyde have often been used as chelating ligands in the field coordination chemistry . Particularly o-Hy-droxy Schiff base derivatives are the most commonly studied because of their interesting photochromic and thermochromic features in the solid state . These properties are due to a change in the n-electron configuration caused by proton transfer [6, 7].
In additional o-Hydroxy Schiff bases have two possible tautomeric forms, the phenol-imine (OH) and the keto-amine (NH) forms. Depending on the tau-tomers, two types of intramolecular hydrogen bonds are observed in Schiff bases: O—H-N in phenol-imi-ne [8, 9] and N-H-O in keto-amine [10, 11] tau-tomers.
Schiff base ligands consist of a variety of substitu-ents with different electron-donating and electron-withdrawing groups, and so they may exhibit interesting electro-chemical properties. The Schiff bases compounds have also been under investigation during last years because of their potential applicability in optical communications and many of them show nonlinear optic (NLO) behavior [12-14]. Conjugated or-
ganic molecules containing both donor and acceptor groups are of great interest for molecular electronic devices . NLO materials have been attractive in recent years with respect to their future potential applications in the field of optoelectronic such as optical communication, optical computing, optical switching, and dynamic image processing [16—18]. Recently, density functional theory (DFT) method in quantum chemical calculations or electronic structure calculations has been accepted as a popular post-HF approach for determination and evaluation of molecular properties such as structural properties, vibrational wavenumbers, molecular energies and electronic, thermodynamic and magnetic properties of molecular systems [19—21].
In this study, we present results of a detailed investigation of the synthesis and structural characterization of (Z)-1-[(2,4-dimethoxyphenylamino)methyl-ene]-naphthalene-2(1#)-one using IR, UV—Vis, and single-crystal X-ray diffraction. The geometric parameters of the compound in the ground state were calculated using the DFT/B3LYP/6-311G(d,p) method. Additionally, the presented in this study was also performed molecular electrostatic potential (MEP), HOMO-LUMO analysis and NLO properties of the title compound. The obtained results are valuable for providing insight into molecular properties of Schiff base compounds.
Fig. 1. Synthesis of the title compound (C19H1-7NO3).
EXPERIMENTAL AND COMPUTATIONAL METHOD
Synthesis of the Compound (Z) -1-[(2,4- dimethoxyphenylamino)methy-lene]naphthalen-2(1#)-one was prepared by reflux-
ing a mixture of a solution containing 2-hydroxy-1-naphthaldehyde (17.22 mg, 0.1 mmol) in ethanol (20 mL) and a solution containing 2,4-dimethoxya-niline (15.32 mg, 0.1 mmol) in ethanol (20 mL). The reaction mixture was stirred for 5 hours under reflux. Single crystals of the title compound for X-ray analysis were obtained by slow evaporation of an ethanol solution. Yield 76%; m.p. 398-402 K (Fig. 1).
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.
Table 1. Crystal data and refinement for the title compound
Chemical formula c19h17no3
Crystal shape/color Prisma/Red
Formula weight 307.34
Crystal system Monoclinic
Space group P2x/c
Unit cell parameters a = 17.8879(11) Â
b = 5.9556(3) Â
c = 14.8976(9) Â
ß = 105.889(5)°
Volume 1526.45(15) Â3
Dx (Mg cm-3) 1.337
^ (mm-1) 0.09
Crystal size (mm3) 0.66 x 0.32 x 0.10
Diffractometer/meas. STOE IPDS II/w-scan
Absorption correction Integration
T J min 0.960
T * max 0.991
No. of measured, 19598, 3017, 2120
Criterion for observed I > 2a(T)
Q Qmax 26
Refinement on F2
R[F2 > 2ct (F2)], wR, S 0.060, 0.123, 1.14
No. of reflection 3017
No. of parameters 212
Weighting scheme w = 1/[ü2( F02 ) + (0.0455P)2 +
P = ( f0) + 2 F2 )/3
Ap ma« APmin (e A-3) 0.16, -0.13
X-ray Single Crystal Structure Determination
A red crystal of the compound with dimensions of 0.66 x 0.32 x 0.10 mm was mounted on goniometer of a STOE IPDS II diffractometer. Measurements were performed at room temperature (296(2) K) using graphite monochromated MoZ„ radiation (X = = 0.71073 A). The systematic absences and intensity symmetries indicated the monoclinic P21/c space group. A total of 19598 reflections (2120 unique) within the 9 range of [2.4° < 9 < 26°] were collected in the scan mode. Cell parameters were determined by using X-AREA software . Absorption correction (^ = 0.09 mm-1) was obtained by the integration method via X-RED32 software . The structure was solved by direct methods using SHELXS-97 . The maximum peaks and deepest hole observed in the final Ap map were 0.16 and -0.13 eA3, respectively. The scattering factors were taken from SHELXL-97 . The molecular graphics were done using Ortep-3 for Windows . The data collection conditions and parameters of refinement process are listed in Table 1.
The molecular geometry is directly taken from the X-ray diffraction experimental results without any constraints. The DFT calculations with a hybrid functional B3LYP (Becke's three parameter hybrid functional using the LYP correlation functional) at 6-311G(d,p) basis set by using Berny method [25, 26] were performed with the Gaussian 03W software package . The harmonic vibrational frequencies were calculated at the same level of theory for the optimized structure and the obtained frequencies were scaled by 0.9682 . By using GaussView molecular visualization program , the vibrational bands assignments have been made. To investigate the reactive sites of the compound the molecular electrostatic potential was evaluated using the B3LYP/6-311G(d,p) method. The linear polarizability and first hyperpolarizability prop-
erties of the compound were obtained from molecular polarizabilities based on theoretical calculations.
RESULTS AND DISCUSSION
Description of the Crystal Structure
The title compound, an Ortep-3 view of which is shown in Fig. 2, crystallizes in the monoclinic space group P21/c with Z = 4 in the unit cell. X-ray structure determinations reveal that the keto tautomer is favoured over the enol tautomer. The Cjj—Nj and C2—O1 bonds of the compound can be determined tautomeric type. The Cjj—Nj bond distance of 1.312 (3) Á, which is consistent with the C—N single bond. The C2=O1 bond [1.285 (3) Á] is consistent with the C=O double bonding. These bond distances are comparable with those of compounds previously reported as keto-amine [10, 11]. In addition to these, the C2—O1 double bond, together with the very short C3—C4 bond [1.343 (4) Á] suggests the presence of a significant quinoidal effect. A similar quinoidal effect was observed for ^-n-proply-2-oxo-1-naphthylideneme-thylamine . The molecular structure of the compound is approximately planar. The dihedral angle between the C1—C10 and C12—C21 rings is 5.73 (5)°. It is also known that Schiff bases may exhibit photo -chromism depending on the planarity or nonplanarity, respectively . The molecular structure is stabilized by an intramolecular N1-H1—O1 hydrogen bond (Table 2) which generates an S(6) ring motif (Fig. 1), according to Graph Set definitions by Bernstein . 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 [2.576 (3) Á] hydrogen bond length .
The crystal structure is stabilized by intermolecular C—H-O hydrogen bonds. Atom C18 in the molecule at (x, y, z) acts as a hydrogen bond donor, via H18B, to atom O1 in the molecule at (x, y + 1, z), so forming a C(10) chain running parallel to the  direction (Fig.
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