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and the imine N atom, namely the phenol-imine tautomer. Schiff
bases are used as starting materials in the synthesis of important
drugs such as antibiotics, antiallergics, antitumors and antifungals
because of their biological activities [9,10]. In addition, their non-
linear properties have an importance for the design of various
molecular electronic devices such as optical switches and optical
data storage devices [11,12]. For Schiff bases, NLO studies provide
the key functions of frequency shifting, optical modulation, optical
switching, optical logic, and optical memory for the emerging tech-
nologies in areas such as telecommunications, signal processing,
and optical interconnections [13–15].
suite. Non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All H atoms were located in a difference Fourier
map and were refined isotropically. Data collection: Stoe X-AREA
[21], cell refinement: Stoe X-AREA [21], data reduction: Stoe XRED
[22]. The general-purpose crystallographic tools PLATON [23] and
ORTEP-3 [21] were used for the structure analysis and presentation
of the results. Details of the data collection conditions and the
parameters of the refinement process are given in Table 1.
2.4. Computational details
A new (E)-2-([3,4-dimethylphenyl)imino]methyl)-3-methoxy-
phenol compound was synthesized and it was determined by sin-
gle crystal X-ray diffraction technique. In the present study, it is
planned to have a joint experimental and theoretical investigation
of FT-IR and UV–vis spectra. According to X-ray, FT-IR and UV–vis
results, the compound shows the enol-imine form, as well the the-
oretical results reveal the structure is more stable state in enol-
imine form rather than keto-amine form. Electronic absorption
spectra of the title compound were predicted for enol-imine and
keto-amine states by using TD-DFT (time-dependent density func-
tional theory) [16–18] in the calculation of electronic excitation
energies for gas and solution phases (different solvent media).
The excitation energies, dipole moments, oscillator strengths and
total energies were also obtained at TD-DFT level at the optimized
geometry. Additionally, it was also planned to illuminate
theoretical determination of the optimized molecular geometries,
HOMO–LUMO energy gap, MEP, NLO, Mulliken charges, NPA and
NBO analysis of the title compound by using density functional
theory (DFT) with B3LYP/6-31G(d,p) basis set. In addition, the
electronic properties of the titled molecule were calculated. The
other important quantities such as ionization potential (I), electron
The molecular structure optimization of the titled compound
and corresponding vibrational harmonic frequencies were calcu-
lated using B3LYP exchange correlation functional [24–30] which
consist of the Lee–Yang–Parr correlation functional in conjunction
with a hybrid exchange functional first proposed by Becke. The
three-parameter hybrid exchange–correlation functional (B3LYP)
[31] employing 6-31G(d,p) basis set [32–34] as implemented in
Gaussian 03 package [35]. Gaussian 03 program package [36]
was used without any constraint on the geometry with the double
split valence basis set along with polarization functions; 6-
31G(d,p).
By combining the results of the GAUSSVIEW [37] program with
symmetry considerations, vibrational frequency assignments were
made with a high degree of accuracy and the vibrations match
quite well with the motions observed using the GAUSSVIEW
program.
For calculating the excitation energies, dipole moments, oscilla-
tion strengths (f), wavelengths (k) and energy gaps of the molecule,
TD-DFT calculations started from gas phase and solution phases
optimized geometries were carried out using the same level of the-
ory. Theoretical UV–vis spectra of the titled compound in enol and
keto forms were also obtained by TD-DFT excited state calculation.
These calculations are also very important in determining solvent
polarity effect on tautomerism. Solvent effects play an important
role in absorption spectrum of the compound, in this paper, the
integral equation formalism polarizable continuum model (PCM)
[38,39] dealing with solvent effect was chosen in total energies,
excitation energies, oscillator strengths, dipole moments and
frontier orbital energies. The calculated values for solvents which
are different dielectric constants, as well as two tautomers of
enol–keto forms have also compared with experimental UV–vis
spectrum results.
affinity (A), electrophilicity index (w), chemical potential (
l),
electronegativity ( ), hardness ( ), and softness (S) are also evalu-
v
g
ated in the way of molecular orbital framework. In the paper, all
calculations are valuable for providing insight into molecular prop-
erties of Schiff base compounds.
2. Experimental and computational methods
2.1. Synthesis
For the preparation of (E)-2-([(3,4-dimethylphenyl)imino]-
methyl)-3-methoxyphenol compound, the mixture of 2-hydroxy-
6-methoxybenzaldehyde (0.5 g, 3.3 mmol) in ethanol (20 ml) and
3,4-dimethylaniline (0.4 g, 3.3 mmol) in ethanol (20 ml) was stir-
red for 2 h under reflux. The crystals suitable for X-ray analysis
were obtained from ethanol by slow evaporation (yield; 72%,
m.p.; 364–366 K).
Table 1
Crystal data and structure refinement parameters.
Chemical formula
Color/shape
Formula weight
Temperature
C16H17N1O2
Orange/Plate
255.31
296 K
2.2. Instrumentation
Crystal system
Space group
Monoclinic
P21/c
The FT-IR spectrum of the title compound was recorded in the
4000–400 cmꢂ1 region with a Bruker Vertex 80V FT-IR spectrome-
ter using KBr pellets. Absorption spectra were determined on
Unicam UV–vis spectrometer.
Unit cell parameters
a = 7.1788(14) Å
b = 25.560(3) Å
c = 7.4256(13) Å
b = 97.231(15)°
1351.7(4) Å3
4
Volume
Z
Density
1.255 Mg mꢂ3
0.083 mmꢂ1
2.3. Crystal structure determination
Absorption coefficient
Diffractometer/meas. meth.
h range for data collection
Unique reflections measured
Total reflection/observed reflections
Goodness of fit on F2
STOE IPDS 2/
1.6–27°
2908
-
-scan
The single-crystal X-ray data were collected on a STOE IPDS II
image plate diffractometer at 296 K. Graphite-monochromated
7617/1730
0.959
R1 = 0.046, wR1 = 0.116
R2 = 0.088, wR2 = 0.135
MoKa radiation (k = 0.71073 Å) and the --scan technique were
used. The structure was solved by direct methods using SHELXS-
97 [19] and refined through the full-matrix least-squares method
using SHELXL-97 [20], implemented in the WinGX [21] program
Final R indices [I > 2
r
(I)]
R indices (all data)
Demircio?lu, Zeynep
