Synthesis, crystal structure and conformational studies of schiff-base compound 2-{[4-(Phenyldiazenyl)Phenyl]Iminomethyl}-5-bromophenol

Article abstract of DOI:10.1007/s10870-011-0214-4

Schiff-base compound 2-{[4-(Phenyldiazenyl)phenyl]iminomethyl}-5-bromo phenol (1), containing an azo group was synthesized from the reaction of p-aminoazobenzene with 5-bromosalicylaldehyde and characterized by elemental analyses, FT-IR spectroscopy and X-ray single-crystal diffraction analysis. Molecular orbital calculation has been carried out using density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the orthorhombic system, space group Pca2₁, with a = 12.1781(2) A, b = 4.4894(10) A, c = 27.7841(5) A, V = 1519.02(5) A³, and Z = 4. Compound 1 displays a trans configuration with respect to the C=N and N=N double bonds. Graphical Abstract: New Schiff-base compound containing an azo-group was synthesized from the reaction of p-aminoazobenzene with 5-bromosalicylaldehyde and characterized by elemental analyses, FT-IR spectroscopy and X-ray single-crystal diffraction analysis. Molecular orbital calculation has been carried out using density functional method (B3LYP) at 6-31G basis set. The title compound displays a trans configuration with respect to the C=N and N=N double bonds.

Full text of DOI:10.1007/s10870-011-0214-4

J Chem Crystallogr (2012) 42:136–140
DOI 10.1007/s10870-011-0214-4
ORIGINAL PAPER
Synthesis, Crystal Structure and Conformational Studies
of Schiff-Base Compound 2-{[4-(Phenyldiazenyl)Phenyl]
Iminomethyl}-5-Bromophenol
•
Aliakbar Dehno Khalaji Karla Fejfarova
•
•
Michal Dusek Alireza Najafi Chermahini
Received: 10 May 2011 / Accepted: 17 November 2011 / Published online: 30 November 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Schiff-base compound 2-{[4-(Phenyldiazenyl)-
phenyl]iminomethyl}-5-bromo phenol (1), containing an
azo group was synthesized from the reaction of p-amin-
oazobenzene with 5-bromosalicylaldehyde and character-
ized by elemental analyses, FT-IR spectroscopy and X-ray
single-crystal diffraction analysis. Molecular orbital cal-
culation has been carried out using density functional
method (B3LYP) at 6-31G basis set. Compound 1 crys-
tallizes in the orthorhombic system, space group Pca21,
coordination chemistry [3–9]. Because of the good thermal
stability of azo compounds, high-density optical data
storage is one of their most important applications and they
are used for digital versatile disc-recordable (DVD-R) as
recording layer [10, 11]. Schiff-base compounds containing
azo group are interesting ligands capable of forming stable
transition metal complexes [3–9] and showing excellent
catalytic activity in various reactions at high temperature
and in the presence of moisture [9].
˚
with a = 12.1781(2) A, b = 4.4894(10) A, c = 27.7841(5) A,
˚
˚
Recently, some Schiff-base compounds containing azo
group have been reported [1, 9]. Herein, we report new
Schiff-base 2-{[4-(Phenyldiazenyl)phenyl]iminomethyl}-
5-bromo phenol (1) containing azo group (Scheme 1).
3
V = 1519.02(5) A , and Z = 4. Compound 1 displays a
˚
trans configuration with respect to the C=N and N=N
double bonds.
Keywords Schiff-base Á Azo group Á Spectroscopy Á
Single-crystal X-ray diffraction
Experimental
Materials and Characterization Techniques
Introduction
All reagents and solvents for synthesis and analysis were
commercially available and used as received without fur-
ther purifications. Infrared spectra were recorded using
KBr disks on a FT-IR Perkin–Elmer spectrophotometer.
Elemental analyses were carried out using a Heraeus CHN-
O-Rapid analyzer.
Compounds containing azo group (–N=N–) have received a
lot of attention in recent years due to research on their
structures [1, 2] and potential applications as a ligands in
Preparation of 2-{[4-(Phenyldiazenyl)Phenyl]
A. D. Khalaji (&)
Department of Chemistry, Faculty of Science,
Golestan University, Gorgan, Iran
e-mail: alidkhalaji@yahoo.com
Iminomethyl}-5-Bromo Phenol (1)
p-Aminoazobenzene (0.197 g, 1 mmol) and 5-bromosali-
cylaldehyde (0.201 g, 1 mmol) were dissolved in mixture
of methanol:chloroform (1:1 v/v, 20 ml) at room temper-
ature. The mixture was stirred and heated for 30 min to
give a red clear solution. The mixture was cooled and the
product allowed crystallizing at room temperature. After
K. Fejfarova Á M. Dusek
Institute of Physics of the ASCR, v.v.i., Na Slovance 2,
182 21 Prague 8, Czech Republic
A. N. Chermahini
Department of Chemistry, Yasouj University, Yasouj, Iran
123

J Chem Crystallogr (2012) 42:136–140
137
Table 1 Summary of crystal data for 1
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C4.75H3.5Br0.25N0.75O0.25
380.2
N
N
N
Orthorhombic
Pca21
O
N
CH3CN / CH3OH
N
+
120
OH
Br
˚
a (A)
12.1781(2)
4.4894(10)
27.7841(5)
1519.02(5)
4
˚
b (A)
˚
c (A)
OH
NH2
3
V (A )
˚
Z
Br
l (mm-1
)
3.78
Scheme1 Synthesis and chemical structure of 1
Tmin
0.400
Tmax
0.720
Measured reflections
Independent reflections
Reflection with I [ 3r(I)
Parameters
18,451
2,359
5 days, red crystals were obtained by slow evaporation of
the solvent. The crystals were collected by filtration and
dried at room temperature. Yield: 91%. Anal. Calc. for
C17H19NO2: C, 60.01; H, 3.71; N, 11.05%. Found: C,
60.12; H, 3.75; N, 11.08%. IR (KBr pellet, cm-1):
3,300–3,500 (–OH), 3054, 2953 (m, C–H aromatic and
aliphatic), 2852 (s, O–HÁÁÁN); 1610 (s, C=N), 1,438–1,586
(C=C aromatic).
2,356
228
Radiation type
Wavelength
Cu Ka
1.54184
1.96
GOF
Index range
-13 B h B 13
-5 B k B 4
-32 B l B 31
0.022
X-Ray Structure Determination
Rint
S
1.48
R[F2 [ 3r(F2)]
0.016
Single crystal with the dimensions 0.39 9 0.27 9
0.12 mm3 of 1 was chosen for X-ray diffraction study.
Crystallographic measurements were done at 120 K with an
Oxford diffraction Gemini four circle CCD difractometer,
wR(F2)
0.057
-3
˚
Dqmax (eA
)
0.13
-3
)
˚
Dqmin (eA
-0.15
˚
Crystal size (mm3)
0.39 9 0.27 9 0.12
with mirrors-collimated Cu Ka radiation (k = 1.54184 A).
The crystal structure was solved by direct methods with the
aid of the program SIR2002 [12] and refined with the
Jana2006 program package [13] by full-matrix least-
squares technique on F2. The molecular structure plot was
prepared by ORTEP III [14]. Hydrogen atoms were mostly
discernible in difference Fourier maps and could be refined
to reasonable geometry. According to common practice
they were nevertheless kept in ideal positions during the
refinement, except the hydrogen of the OH group which
position was refined using a restraint on the O–H distance.
The isotropic atomic displacement parameters of hydrogen
atoms were evaluated as 1.2 Ueq of the parent atom. Crys-
tallographic data and details of the data collection and
structure solution and refinements are listed in Table 1.
frequency calculations were used to characterize all sta-
tionary points as minima (the number of imaginary fre-
quencies NIMAG = 0). All calculations were performed on
a Pentium IV Processor personal computer without any
constraint on the geometry.
Results and Discussion
Synthesis and Spectroscopy
The Schiff-base ligand 1 was prepared by the condensation
between p-aminoazobenzene with 5-bromosalicylaldehyde
(1:1 molar ratio) in mixture of methanol:chloroform (1:1 v/v,
20 ml) at room temperature as shown in Scheme 1. This
compound is stable at room temperature and soluble in
coordinated organic solvents such as DMSO and DMF and
it is insoluble in common organic solvents such as EtOH,
MeOH, CH3CN, CH3Cl and CH2Cl2. The experimental
Molecular Modelling Studies
Density functional theory (DFT) [15] calculations were
performed using Gaussian 98 program [16]. Geometries of
all species were optimized using 6–31G(d) and 6–31 ?
G(d) basis sets at the DFT level [17–19]. Vibrational
123

138
J Chem Crystallogr (2012) 42:136–140
Fig. 1 The molecular structure
of 1, showing 50% probability
displacement ellipsoids. An
intramolecular hydrogen bond is
shown as a dashed line
X-Ray Structure Analysis
analyses results of 1 are in good compliance with the
theoretical calculations.
Compound 1 crystallizes in the non-centrosymmetric
orthorhombic system, space group Pca21, with one mole-
cule in the asymmetric unit. The molecular structure of the
asymmetric unit of 1 with the atom numbering scheme is
given in Fig. 1. The molecule adopts a trans configuration
with respect to the C=N and N=N double bonds. The bond
lengths and angles are within the normal ranges [24].
Selected bond lengths and angles are given in Table 2.
Bond lengths and angles within the aromatic rings and
azomethine group are consistent with those expected for
FT-IR Spectra
In the FT-IR spectra, the ligand exhibits bands at
3,300–3,500 and 2,923–3,054 cm-1 that are assignable to
t(OH) and t(Ar–CH) [9, 20]. The stretching frequency
observed at 2,852 cm-1 shows the presence of O–HÁÁÁN
intramolecular hydrogen bond [21]. The stretching fre-
quency at 1,610 cm-1 exist due to the vibration of the
azomethine (C=N) group [22, 23].
Table 2 Selected bond
A
B
C
D
Exp.
lengths, bond angles and
dihedral angles for 1 and the
Br1–C18
1.908
1.907
1.358
1.260
1.418
1.413
1.401
1.282
1.465
–
1.907
1.368
1.260
1.418
1.414
1.401
1.283
1.464
–
1.907
1.370
1.260
1.418
1.414
1.401
1.284
1.467
–
1.8986(17)
1.349(2)
isomers A–D calculated at the
B3LYP/6–31 ? G(d) level of
theory
O1–C15
1.344
1.260
1.418
1.415
1.405
1.293
1.451
1.7524
115.3
115.2
121.6
124.7
115.4
123.1
117.8
122.3
124.9
115.7
119.4
120.0
-179.7
0.5
N1–N2
1.232(2)
N1–C1
1.462(3)
N2–C7
1.461(3)
N3–C10
1.413(3)
N3–C13
1.290(2)
C13–C14
1.448(3)
H10–N3
1.834(4)
N2–N1–C1
N1–N2–C7
C10–N3–C13
N1–C1–C2
N1–C1–C6
N3–C10–C9
N3–C10–C11
N3–C13–C14
N2–C7–C8
N2–C7–C12
Br1–C18–C17
Br1–C18–C19
C7–N2–N1–C1
C2–C1–N2–N1
C11–C10–N3–C13
N3–C13–C14–C15
115.2
115.4
119.8
124.8
115.4
123.1
118.0
125.6
124.9
115.7
119.7
120.0
-179.6
0.6
115.3
115.2
120.5
124.8
115.7
123.1
117.9
122.9
124.8
115.4
119.4
119.9
-179.7
0.9
115.1
115.4
120.2
124.9
115.7
123.2
117.9
121.8
124.8
115.4
119.3
119.7
-179.7
0.3
110.7(2)
111.63(19)
122.35(15)
126.6(3)
113.3(3)
125.39(19)
115.42(18)
120.65(16)
127.6(2)
112.0(3)
118.69(15)
119.70(12)
-180.0(5)
179.3(3)
Bond lengths in angstrom,
bond angles and dihedral angles
in degree
-147.5
0.9
-142.0
2.95
39.4
-144.0
-177.8
177.55(18)
2.8(3)
-172.9
123

J Chem Crystallogr (2012) 42:136–140
139
also presented in the Table 2. Based on our calculation and
confirmed with experimental data two phenyl rings linked
to azo group are coplanar. In addition, based on the
experimental data the phenyl ring connected to imine group
Table 3 Different type of hydrogen bonds in 1
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
C4–H4ÁÁÁBr1
C3–H3ÁÁÁBr1
C19–H19ÁÁÁO1
C12–H12ÁÁÁN1
C13–H13ÁÁÁO1
O1–H10ÁÁÁN3
C16–H16ÁÁÁBr1
0.96
0.96
0.96
0.96
0.96
0.83(2)
0.96
3.09
3.09
2.84
3.01
2.64
1.85(2)
3.01
3.983(2)
3.739(2)
3.606(2)
3.699(3)
3.453(2)
2.587(2)
3.6691(19)
126.15
154.54
137.45
129.58
142.56
147(2)
127.34
sp2 carbon atom. For the imine nitrogen atom, N3, the bond
˚
length N3–C13 of 1.290(2) A is consistent with double
˚
bonds and the bond length N3–C10 of 1.413(3) A is con-
sistent with single bond. The bond angles C10–N3–C13 of
122.35(15)°, and N3–C13–C14 of 120.65(16)° confirm
their sp2 character for N3 and C13 atoms, respectively. The
three benzene rings, azomethine and azo groups are prac-
tically co-planar. Ortho position to the imine group of
Schiff-base occupied with the OH is interesting due to the
existence of O–HÁÁÁN hydrogen bond and tautomerism
between enol-imine and keto-amine form [21, 25]. In this
structure, there is intramolecular O1–H1ÁÁÁN3 hydrogen
bond (Fig. 1; Table 3).
In view along b in the crystal structure, slabs are con-
nected by weak C–HÁÁÁBr interactions. The slabs are
extended along ab plane and the molecules are connected
with C–HÁÁÁO and C–HÁÁÁN interactions. The O–HÁÁÁN
interaction is only intramolecular (See Fig. 2; Table 3).
DFT Calculations, Geometry and Energies
In the gas phase the four conformers for the compound 1
were considered. The structure and selected numbering of
these isomers are presented in the Fig. 3. In the conformers
A and B the hydroxyl group is near to the nitrogen of imine
group. However, only in the conformer A hydrogen
bonding is possible between hydroxyl and imine groups. In
the isomers C and D the hydroxyl group is away from the
nitrogen imine group.
Fig. 2 Crystal packing of 1 viewed along the c axis showing the 3D
hydrogen bond chain parallel
2
6
1
N
1
N
N
N2
N
N
N
N
N
N
N
The optimized bond lengths and selected bond angles
for the preferred geometries of conformers A–D deter-
mined at B3LYP/6–31 ? G(d) level are presented in
Table 2 in accordance with the atom numbering scheme of
the molecule shown in Fig. 3. The bond lengths and angles
obtained from DFT calculation for the conformer A are in
very good agreement with experimental values. The aver-
age discrepancy between calculated and experimental
values is 0.5–4% for bond lengths and 5–5.6% for angles.
The maximal difference was found for N1=N2 bond (4%)
and N2–N1–C1 angle (5.6%) (See Table 2 for compari-
son). The calculated dihedral angles of compound 1 are
7
8
12
11
10
3 N
13
H1
H
O
14
1
O
O
O
19
H
H
15
1
16
Br
18
Br
Br
Br
17
D
A
B
C
Fig. 3 The structure and selected numbering of four isomers
of compound 1 considered in the gas phase
123

140
J Chem Crystallogr (2012) 42:136–140
Table 4 The calculated total energies and relative stabilities of isomers of compound 1 in the gas phase
A
B
C
D
B3LYP/6–31G(D)
-3543.6013108
-3543.5799638
13.40
-3543.5830184
11.48
-3543.5859885
9.61
0
B3LYP/6–31 ? G(D)
-3543.6622419
-3543.6416987
12.89
-3543.6448064
10.94
-3543.64772341
9.11
0
Total energies in Hartree, relative stabilities in kcal/mol
Acknowledgments The authors acknowledge the Golestan Uni-
versity (GU) and Yasouj University (YU) for partial support of this
study and the institutional research plan No. AVOZ10100521 of the
Institute of Physics and the project Praemium Academiae of the
Academy of Sciences of the Czech Republic.
is coplanar with that. However, the calculated dihedral
angle for C11–C10–N3–C13 (-147.5° for the conformer
A) shows deviation from planarity. The results of calcu-
lated geometrical parameters of other isomers of compound
1 in the gas phase are also in agreement with experimental
data except the dihedral angle C11–C10–N3–C13.
References
The results of calculated total energies and relative
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presented in the Table 4. In agreement with experimental
results obtained in the solid state, DFT calculations favour
isomer 1 as the most stable one in the gas phase. It is
evident that intramolecular hydrogen bonding stabilizes the
isomer A. The order of stability predicted by DFT method
using 6–31G(d) and 6–31 ? G(d) was found as
A [ D [ C [ B. Bases on our calculations the stability of
A isomer over D, C and B was found 9.61, 11.48, and
13.40 kcal/mol, respectively.
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Conclusions
New Schiff-base ligand 2-{[4-(Phenyldiazenyl)phenyl]im-
inomethyl}-5-bromo phenol (1) containing azo group, was
synthesized from the reaction of p-aminoazobenzene with
5-bromosalicylaldehyde and characterized by elemental
analyses and FT-IR spectroscopy. Its crystal structure was
determined from single-crystal X-ray diffraction data. The
molecular geometry of this compound was analyzed by
Density functional theory. The most stable molecular
conformation of 1 from DFT method calculation agrees
well with that obtained from X-ray structure determination.
Supplementary Data
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57:257
23. Khalaji AD, Najafi Chermahini A, Fejfarova K, Dusek M (2010)
Struct Chem 21:153
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Taylor R (1987) J Chem Soc Perkin Trans 2:S1
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Crystallographic data (excluding structure factors) for the
structure reported in this paper has been deposited with the
Cambridge Crystallographic Center, CCDC No. 851503
(1). Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, fax: ?44 1223 336 033, e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk.
123