T.A. de Toledo et al. / Journal of Molecular Structure 1097 (2015) 106–111
107
(20 mmol) and salicylaldehyde (10 mmol) in ethanol solution
Results and discussions
(40 mL) under stirring by two hours, as describe in Ref. [1]. The
crystals of Salophen were grown by slow evaporation method at
room temperature.
Molecular structure
The molecular structure of Salophen comprises three rings,
named here as R1, R2 and R3. R1 is formed by atoms from C1 to
C6, which comes from a 1,2-phenilenediamine. R2 and R3 are
formed by atoms from C8 to C13 and C15 to C20, which comes
from salicylaldehyde derivative. Fig. 1 displays the atom number-
ing scheme of Salophen molecule using ball and stick style. In
Table 1 the experimental X-ray data (reported in Refs. [1] (Exp.
A) and [2] (Exp. B)) and calculated geometrical parameters (bond
distances, bond angles and dihedral angles) for Salophen are
shown. To better discussion of the results presented in this study,
the data taken from reference [2] will be show inside of parenthe-
ses. In the solid state, the asymmetric unit of Salophen presents the
formation of intra-molecular hydrogen bond between H15. . .N2
and H16. . .N1 atoms with distances of 1.709 (1.780) Å and 1.670
(1.670) Å, while calculation gives the NAH bond distance of 1.72
Å. According to the literature [1,2], the molecular structure of
Salophen exhibits a torsion angle between R1 and R2 rings com-
prised C4AC5AN2AC14 atoms and between R1 and R3 ring com-
prised C5AC4AN1AC7 atoms with value of ꢁ132.18° (ꢁ131.69)
and of 177.96° (178.12°), respectively, while DFT calculations pre-
sented in this study predicted the value of 145.8° for both torsion
angle. The main difference between DFT predictions and experi-
mental crystallographic data for the torsion angle are associated
with effect of crystal packing forces acting on molecule in the lat-
tice, since the calculations was performed in an asymmetric unit of
the Salophen. Finally, it is worth to mention that the comparison
between experimental and calculated data may results in useful
Sample characterization
The structure elucidation was confirmed by 1H and 13C chemical
shifts by using a NMR spectrometer BRUKER DRX – 400 MHZ, with
TMS as internal standard. The crystals were prepared in DMSO-d6
solutions. Analytical data: 1H NMR (400 MHz, DMSO-d6) d 12.95 (d,
J = 12.0 Hz, 2H, OH), 8.94 (s, 2H, HC = N), 7.67 (dd, J = 7.6, 1.1 Hz,
2H), 7.51 – 7.36 (m, 6H, aromatic), 6.98 (dd, J = 12.2, 4.7 Hz, 4H,
aromatic). 13C NMR (101 MHz, DMSO-d6)
d 163.94, 160.28,
142.17, 133.33, 132.35, 127.58, 119.65, 119.39, 118.98, 116.57.
Raman spectrum in the wavenumber region from 5 cmꢁ1 to
4000 cmꢁ1 at atmospheric condition was recorded using
a
LabRam HR Evolution Horiba Jobin-Yvon spectrometer at 2 cmꢁ1
nominal resolution with a HeANe laser emitting at 632.8 nm.
The spectrum was obtained using five accumulations and the
acquisition time was 30 s. The FT-IR spectrum was collected on
Varian-660 spectrometer in the spectral range 240–4000 cmꢁ1
using KBr pellets technique. The SEM images of Salophen was
acquired on JEOL JSM6460LV operated with applied tension of
15 kV on the crystals were glued onto aluminum stub and sput-
tered gold.
Computational methods
The DFT calculations were carried out starting from experimen-
tal X-ray data given in reference [1], carried out using the
Gaussian03 package [23]. The Lee–Yang–Parr correlation func-
tional (B3LYP) [24,25] and the basis set 6-31G (d,p) augmented
by ‘d’ polarization functions on heavy atoms and ‘p’ polarization
functions on hydrogen atoms were used. The DFT calculations were
performed in gas phase using an isolated molecule of the unit cell
described in reference [1]. The harmonic vibrational frequencies
were calculated at optimized molecular structure and
non-negative frequency was obtained. Therefore, in our calcula-
tions we have obtained a true minimum of potential energy. The
vibrational modes analysis based on potential energy density
(PED) was performed using VEDA 4 software package [26].
resource
information
about
the
intermolecular
and
intra-molecular interactions, which is usually associated with bio-
logical activities of the organic materials.
Crystal morphology
The SEM images of Salophen crystals are shown in Fig. 2. It can
be seen from Fig 2(a) and (b) that the crystals are mainly composed
of many microtubes. In Fig. 2(c), it can be observed a large number
of crystals with different size and shape on crystal surface, indicat-
ing that the crystals were possibly formed by an agglomeration of
smaller crystal and then gradually fused to form a bigger one. A
similar fact is also described in literature [22].
The calculated IR and Raman spectra were obtained from the
sum of the Lorentzian functions with full width at half maximum
(FWHW) of 4 cmꢁ1. In addition, the calculated Raman intensity
given by DFT calculations was converted to relative intensity (I)
by using the expression derived from Raman scattering activity
(Si) theory, I ¼ 10ꢁ12
ðm0
ꢁ
mi
4mꢁi 1Si; where m0 is the wavenumber
Þ
of the laser source excitation and mi is the wavenumber normal
mode [27]. In order to improve the comparison with experimental
spectrum, the theoretical spectra were scaled by a scale factor of
0.9613 and 0.9513 in the spectral region below and above
1800 cmꢁ1, respectively. The scaling factors were used in this study
to offset the systematic error caused by neglecting anharmonicity,
electron density and basis set truncation effects [28–30]. The
higher wavenumber region, above 1800 cmꢁ1, contains vibrations
composed mainly by localized hydrogen stretches, whereas bellow
1800 cmꢁ1 contains heavy atom in-plane stretches and bends,
out-of-plane and torsional modes. High-energy modes can be
expected to be more anharmonic, leading to greater errors because
of the harmonic approximation [31,32]. Therefore, dual scaling fac-
tors were determined to improve the agreement between com-
puted and observed frequencies. Finally, the experimental and
theoretical Raman spectra were compared.
Fig. 1. Salophen molecule: atomic number scheme using ball and stick style.
De Toledo
