Characterization, and crystal structure of thiophenyl-2-methylidene-2- aminophenol

Article abstract of DOI:10.1134/S0022476613010423

The Schiff base thiophenyl-2-methylidene-2-aminophenol (ImineOH) is obtained from a stoichiometric mixture of 2-thiophenecarboxaldehyde and 2-aminophenol in ethanol under reflux at 90 C. Its crystal structure is determined by single crystal X-ray diffract

Full text of DOI:10.1134/S0022476613010423

Journal of Structural Chemistry. Vol. 54, No. 1, pp. 269-273, 2013
Original Russian Text Copyright © 2012 by A. Cuin, G. A. Pereira, A. J. Bortoluzzi, A. C. Massabni, P. P. Corbi
CHARACTERIZATION, AND CRYSTAL STRUCTURE
OF THIOPHENYL-2-METHYLIDENE-2-AMINOPHENOL
A. Cuin,1 G. A. Pereira,1 A. J. Bortoluzzi,2 A. C. Massabni,3
©
DOI: 10.1134/S0022476613010423
and P. P. Corbi4
The Schiff base thiophenyl-2-methylidene-2-aminophenol (ImineOH) is obtained from a stoichiometric
mixture of 2-thiophenecarboxaldehyde and 2-aminophenol in ethanol under reflux at 90ꢀC. Its crystal
structure is determined by single crystal X-ray diffraction. ImineOH packs in an orthorhombic unit cell in
the Pbca space group with the unit cell parameters a = 16.942(4) Å, b = 13.4395(11) Å, and
c = 17.5857(12) Å, V = 4004.1(10) Å3, Z = 16. Strong hydrogen bonds are present in the ImineOH
structure. Apart from the X-ray study, ImineOH was characterized by elemental analysis (CHN-S) and FT–
IR (4000 cm–1 to 400 cm–1), UV-Vis and 13C, 1H, and 15N NMR spectroscopic measurements.
Keywords:
Schiff
base,
thiophenyl-2-methylidene-2-aminophenol,
2-aminophenol,
2-thio-
phenecarboxaldehyde.
Schiff bases are compounds containing the azomethine group (RC=N–) formed by condensation of a primary amine
with the carbonyl group of an aldehyde or a ketone. In this study, the Schiff base thiophenyl-2-methylidene-2-aminophenol,
named ImineOH (molecular formula C11H9NOS), is presented. The ImineOH isomer, 2-[(4-hydroxyphenyl)
iminomethyl]thiophene, was previously reported in the literature [1]. Since Schiff bases contain S, N, and/or O donor atoms,
they have been extensively used as ligands in coordination chemistry [2]. They have shown promising applications in the
biological field, for example, as potent anticoagulants [3]. Furthermore, a large number of Schiff bases or their metal derivatives
have been investigated for their interesting properties [4]. Schiff base compounds remain an important and popular area of
research due to their easy synthesis, versatility, and a number of applications, especially in biological systems [5, 6].
The aim of the present work is to report the molecular and crystal data of the organic compound: thiophenyl-2-
methylidene-2-aminophenol.
Experimental methods. All NMR data were obtained in CDC13. Elemental analyses of carbon, hydrogen, nitrogen,
and sulfur were performed using a CHNS–O EA 1110 Analyzer (CE Instruments). The infrared spectrum was recorded on a
Perkin Elmer Spectrum 2000 FT–IR Spectrophotometer in the range 4000-400 cm–1. The sample was prepared as a KBr
pellet. The UV-Vis spectrum was recorded in DMSO solution using a Shimadzu UV-Vis spectrophotometer in the range
1
300–800 nm. The H, 13C and the [1H–15N] correlation nuclear magnetic resonance spectra (HMBC) were recorded on a
Bruker Avance III 400 MHz (9.395 T) using a 5 mm probe at temperature of 298 K. The 1H NMR spectrum was obtained at
400.1 MHz, while the 13C–{1H} spectrum was obtained at 100.6 MHz. For 13C NMR: pulse 14.75 ꢁs (90ꢀ); delay time 2 s.
For 1H–15N NMR: 15N pulse 27.50 ꢁs (90ꢀ); delay time 1 s.
1Chemistry Department, Exact Sciences Institute, UFJF Juiz de Fora, MG, Brazil; alexandre_cuin@yahoo.com,
2
3
alexandre.cuin@ufjf.edu.br. LABINC, Chemistry Department, UFSC Florianópolis, SC, Brazil. Inorganic and General
4
Chemistry Department, Institute of Chemistry, UNESP Araraquara, SP, Brazil. Institute of Chemistry, Campinas State
University, UNICAMP Campinas, SP, Brazil. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii,
Vol. 53, No. 6, pp. 1225-1229, November-December, 2012. Original article submitted October 19, 2011.
0022-4766/13/5401-0269
269

TABLE 1. Crystal Data and Structure Refinement for ImineOH
Empirical formula
C11H9NOS
Formula weight
Temperature, K
203.25
293(2)
Wavelength, Å
0.71073
Crystal system
Orthorhombic
Space group
Pbca
Unit cell dimensions a, b, c, Å
16.942(4), 13.4395(11), 17.5857(12)
3
Volume, Å
4004.1(10)
16
Z
3
Density (calculated), mg/m
1.349
–1
Absorption coefficient, mm
0.286
F(000)
1696
Crystal size, mm
0.50×0.36×0.23
2.25 to 25.97
θ range for data collection, deg
Index ranges
–20 ≤ h ≤ 0, –16 ≤ k ≤ 1, 0 ≤ l ≤ 21
Reflections collected
Independent reflections
Absorption correction
Refinement method
4252
3911 [R(int) = 0.0262]
None
2
Full-matrix least-squares on F
Data/restraints/parameters
3911/0/261
1.021
2
GOOF on F
R1 = 0.0552, wR2 = 0.1412
R1 = 0.1539, wR2 = 0.1555
0.291 and –0.333
Final R indices [I > 2σ(I )]
R indices (all data)
–3
Largest diff. peak and hole, e⋅Å
TABLE 2. Selected Bond Lengths (Å) and Angles (deg)
Bond angles, deg
C1–N1–C11
Bond lengths, Å
Bond angles, deg
C1–C2–S1
N1–C1
1.281(4)
1.434(4)
1.353(4)
1.681(4)
1.716(3)
118.1(3)
91.23(18)
125.8(3)
123.6(3)
112.8(2)
123.6(3)
122.4(3)
117.8(3)
116.9(3)
123.9(3)
N1–C11
O1–C12
S1–C5
C5–S1–C2
N1–C1–C2
C3–C2–C1
C3–C2–S1
C16–C11–N1
C12–C11–N1
O1–C12–C13
O1–C12–C11
S1–C2
X-ray crystallography. A prismatic yellow crystal was selected for the crystallographic analysis; it was fixed at the
end of a glass fiber. Experimental data were recorded on an Enraf-Nonius CAD-4 diffractometer at room temperature
(graphite-monochromated MoK radiation, λ = 0.71073 Å). Cell parameters were determined on the setting angles of 25
α
carefully centered reflections in the θ range from 5.21° to 19.19°. The intensities were measured using the ω/2θ scan
technique. Collected reflections were corrected for Lorentz and polarization effects [7]. The structure was solved by direct
2
methods with SIR97 [8] and refined by the full-matrix least squares procedure based on F with the SHELXL97 software [9].
The hydrogen atoms attached to carbon atoms were placed at idealized positions, with C–H distances and Ueq values taken
from the default settings of the refinement program and treated by the riding model. Hydrogen atoms of the alcohol groups
were found from the Fourier difference map and refined as free atoms. All non-hydrogen atoms were refined with anisotropic
displacement parameters. Further crystallographic information is listed in Table 1 and a selection of bond lengths and angles
are presented in Table 2.
270

Fig. 1. ORTEP drawing of ImineOH with displacement
ellipsoids plotted at a 40% probability level.
Fig. 2.
independent molecules presented
in the unit cell. Intermolecular
Projection
of
two
hydrogen
interactions
are
indicated by dashed lines.
TABLE 3. Hydrogen Bond Distances (Å) and Angles (deg) in ImineOH
D–H…A
d(D–H)
d(H…A)
d(D…A)
∠(DHA)
O1–H1O…N2
O2–H2O…N1
0.81(4)
0.81(4)
2.02(4)
1.99(4)
2.830(4)
2.770(4)
176(4)
160(4)
Synthesis. The starting compounds (2-thiophenecarboxaldehyde and 2-aminophenol) were purchased from Sigma-
Aldrich Laboratories. A mass of 2.332 g (21.4 mmol) of 2-aminophenol was dissolved in 30 ml of hot ethanol and 2.397 g
(21.4 mmol) of 2-thiophenecarboxaldehyde were added slowly to the hot alcoholic 2-aminophenol solution. The solution was
kept under reflux for 3 h at about 60°C. After the reaction time, anhydrous sodium sulfate was added to eliminate traces of
water. The final alcoholic solution was concentrated until the formation of a viscous liquid. Then, microcrystalline powder
was obtained by adding 30 ml of absolute methanol. Suitable crystals were obtained by slow evaporation of the filtrated
methanolic solution.
Results and discussion. Crystal structure. The ORTEP view of ImineOH is shown in Fig. 1. Crystal and data
collection of the X-ray structural analysis are shown in Table 1. There are two independent molecules of ImineOH in the
asymmetric unit. The independent molecules have slight differrences in their conformation, which can be evidenced by
different C11–N1–C1–C2 torsion angles of 175.4(3)° and 176.3(3)° and by the dihedral angles between the mean planes of
phenyl and thiophenyl rings of 43.00(12)° and 44.97(14)°. The bond lengths and angles are very close to each other for the
equivalent atoms of both molecules. Selected bond lengths and angles for one ImineOH are presented in Table 2. Hydrogen
bonds are listed in Table 3.
The N1–C1 (1.281 Å) and N1–C11 (1.434 Å) bond lengths are slightly shorter than the C=N double and single bond
distances due to electronic conjugation with the thiophenyl ring, which is almost coplanar with the C=N double bond. The
mean plane of phenol is twisted about 40° in both molecules [10].
Two independent molecules are linked by strong intermolecular hydrogen bonds between the alcohol groups as
donors and the nitrogen atom of the imine group as the acceptor. Geometric parameters for the hydrogen bonds of the title
compound are listed in Table 3, while the hydrogen bonds between two ImineOH molecules are shown in Fig. 2.
–1
Molecular structure. The molecular formula of ImineOH (C11H9NOS, MW 203.1 gmol ) was confirmed by the
elemental analysis of C, H, N, and S. The experimental data on weight concentrations match with the calculated ones. Anal.
calc. for C11H9NOS (%): C 65.0; H 4.47; N 6.89; S 15.8%. Found (%): C 65.(0); H 4.3(5); N 6.7(5); S 15.5%. M.P.: 80.5-
81.0°C.
271

13
Fig. 3. C NMR (a) and H– N HMBC NMR (b) spectra of ImineOH.
1
15
The FT–IR analysis showed the presence of a strong and characteristic band of N=CR of the azomethilene group of
–1
imines at 1606 cm . Other two main moieties present in the FT–IR spectrum of ImineOH are the phenol group and the
–1
thiophene skeleton. Usually, a broad and medium band for the –OH ortho-substitution of the phenyl group at 3466 cm is
–1 –1
assigned to the νO–H stretching frequency. Three bands are assigned to 2-monosubstituted thiophene at 1354 cm , 1419 cm ,
–1
and 1379 cm corresponding to the in-plane C=C stretching frequency (νC=C) of the aromatic moiety [11].
The UV-Vis spectrum shows a band at 294 nm and a shoulder at 306 nm due to the localized p–p* transition.
Another band due the azomethine chromophore group is centered at 355 nm.
13
13
The C NMR spectrum of ImineOH is shown in Fig. 3a. The major peaks in the C NMR spectrum were observed
at 152.3 ppm (C1, RC=N), 149.8 ppm (C12, CAr–OH), 142.9 ppm (C11, CAr–N), 135.1 ppm (C2, S–C–CN). Peaks due to
other carbon atoms of the phenyl and thiophenyl groups are observed at 132.6 ppm, 130.8 ppm, 128.9 ppm, 128.0 ppm,
1
120.1 ppm, 115.8 ppm, and 116.1 ppm. In the H NMR spectrum, a peak at δ = 8.82 ppm (s) is due to 1H, (H–C1). Another
single peak due 1H, –OH is observed at δ = 9.99 ppm. The hydrogen atoms of the phenyl group are observed at δ = 7.27 ppm
(d, H–C13), δ = 6.94 ppm (t, H–C14), δ = 7.23 ppm (t, H–C15), δ = 7.33 ppm (d, H–C16), and the hydrogen atoms of the
thiophenyl group are observed δ = 7.30 ppm (d, H–C3) and δ = 7.06 ppm (m, H–C4 and H–C5) [12]. The assignment of the
1
nitrogen resonance in the two-dimensional H– N NMR spectrum was performed by the correlation between N observed at
15
15
289.9 ppm, with protons at 8.82 ppm (H–C1, J2), at 7.33 ppm (H–C16, J3), and at 7.30 ppm (H–C3, J3). The interaction
15
1
1
15
13
between N and H at 9.99 ppm (s, OH) was not observed. The H– N and C NMR spectra are shown in Fig. 3b.
As discussed above, the single crystal X-ray diffraction study shows that ImineOH has only E configuration around
the C=N bond. No evidences of the Z configuration of ImineOH were obtained. The keto-amine tautomeric equilibrium can
272

be present for Schiff bases such as ImineOH [13]. The conversion energies between the tautomers are very low and the
structures can be present in the gas phase or in a cold solution [14].
Supplementary material. Crystallographic data for the structure reported in this paper have been deposited with the
Cambridge Crystallographic Data Center. Copies of the data (CCDC 812820) can be obtained free of charge upon application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (e-mail: deposit@ccdc.cam.ac.uk).
The authors are grateful to the Brazilian Agencies FAPEMIG (process CEX-APQ-00173/09) and CNPq (process
472468/2010-3) for the financial support.
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