Conformational and structural analysis of N-N′-bis (4-methoxybenzylidene)ethylenediamine

Article abstract of DOI:10.1016/S0022-2860(01)00469-0

The Schiff base compound, N-N′-bis(4-methoxybenzylidene)ethylenediamine (C₁₈H₂₀N₂O₂) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystalliz

Full text of DOI:10.1016/S0022-2860(01)00469-0

Journal of Molecular Structure 570 ꢀ2001) 91±95
www.elsevier.com/locate/molstruc
Conformational and structural analysis of N-N 0-bis
ꢀ4-methoxybenzylidene)ethylenediamine
a,
C. Unaleroglu , B. Temelli , T. Hokelek
a
b
È
*
Æ
È
aDepartment of Chemistry, Hacettepe University, 06532 Beytepe-Ankara, Turkey
bDepartment of Physics, Hacettepe University, 06532 Beytepe-Ankara, Turkey
Received 17 August 2000; accepted 3 January 2001
Abstract
The Schiff base compound, N-N 0-bisꢀ4-methoxybenzylidene)ethylenediamine ꢀC18H20N2O2) has been synthesized and its
crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space
ꢀ
ꢀ 3
group P21=n with a ˆ 10:190ꢀ1†; b ˆ 7:954ꢀ1†; c ˆ 10:636ꢀ1† A; b ˆ 111:68ꢀ1†8; V ˆ 801:1ꢀ1† A ; Z ˆ 2 and Dcal
ˆ
1:229 Mg m23: The title structure was solved by direct methods and re®ned to R ˆ 0:056 for 2414 re¯ections ‰I . 3:0sꢀI†Š
by full-matrix anisotropic least-squares methods. The energy pro®le of the compound was calculated by PM3 method as a
function of u[N10 ±C90 ±C9±N1]. The most stable molecular structure of the title compound is the anti conformation, which is
different in energy by 5.0 and 1.0 kcal mol21 from the eclipsed conformation I and gauche conformations, ꢀIII and V),
respectively. q 2001 Elsevier Science B.V. All rights reserved.
Keywords: Structural analysis; Schiff base; Chelating ligands
1. Introduction
of reports about the free Schiff bases in the literature
[10±15]. The phenyl derivative Schiff bases are used
as corrosion inhibitors for aluminum in hydrochloric
solution [16]. Knowing the structures of free Schiff
bases in solution and in solid state is important in
view of the comparison with the conformational
analysis results. For these reasons, the synthesis,
structural and conformational studies of the title
compound were undertaken.
Schiff bases and their biologically active complexes
have been studied during the last decade. Schiff bases
have often been used as chelating ligands in the ®eld
of coordination chemistry [1] for obtaining thermo-
tropic liquid crystalline polymers [2,3] and their metal
complexes have been used as radiopharmaceuticals
for cancer targeting [4], as dioxygen carriers [5] and
as model systems for biological macromolecules
[6,7]. The Schiff base complexes have also been
used in catalytic reactions [8,9]. Although a series
of Schiff base complexes have been investigated crys-
tallographically, there are only a very limited number
2. Experimental
2.1. Reagents and techniques
AnisalaldehydeꢀBDH), ethylenediamineꢀAldrich),
methanol and ethanolꢀCarlo Erba)were used in this
study. Infrared spectrum was recorded using a
* Corresponding author. Tel.: 1903-122992163; fax: 1903-
122992163.
E-mail address: canan@eti.cc.hun.edu.tr ꢀC. Unaleroglu).
È
Æ
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-2860ꢀ01)00469-0

È
Æ
C. Unaleroglu et al. / Journal of Molecular Structure 570 22001) 91±95
92
Table 1
Experimental data and structure-re®nement parameters
SHIMADZU FTIR-8101 spectrophotometer as KBr
discs, in the range of 400±4000 cm21 UV-visible
spectrum was measured using a UNICAM UV/VIS
spectrophotometer in CH3OH solvent, in the range
of 190±600 nm. Melting point was measured on a
Gallenkamp apparatus using a capillary tube.
Compound
Color/shape
C18H20N2O2
Colorless/plate
Formula weight
Space group
TemperatureꢀK)
Cell constants
296.37
P21/n
298
a ˆ 10.190ꢀ1), b2 ˆ 7.954ꢀ1),
2.2. Synthesis of N-N 0-bis
24-methoxybenzylidene)ethylenediamine
Ê
c ˆ 10.636ꢀ1) A, b ˆ 111.68ꢀ1)8
Ê 3
Cell volume ꢀA )
Formula units/unit cell
801.1ꢀ1)
2
DcalcꢀMg m23
)
1.229
Anisalaldehyde ꢀ3.62 ml, 33.6 mmol) was
dissolved in ethanol ꢀ20 ml). Then ethylenediamine
ꢀ1.00 ml,14.66 mmol) was added and the solution
was heated at 608C. After 1 h, the reaction was
completed. The product was ®ltered and crystallized
in methanol, 3.9 g ꢀ89.78%) yield, m.p. 110.88C. IR
m
calcꢀmm21
)
0.65
Diffractometer/scan
Radiation used, graphite
monochromator
Enraf±Nonius CAD-4/v22u
Ê
Cu Kaꢀl ˆ 1.54184 A)
Maximum crystal
dimensionꢀmm)
0.20 £ 0.20 £ 0.30
p
p
C±H
ꢀKBr, cm21); 2840±2900 ꢀ C±H aliphatic); 3080ꢀ
Standard re¯ection
Decay of standard
Re¯ections measured
u ꢀmax) ꢀ8)
3
p
p
p
aromatic); 1641 ꢀ ꢀCyN); 1109 ꢀ C±O).
max
, 1%
3446
74.35
ꢀCHCl3, nm), 304.
Range of h, k, l
29 # h # 9, 211 # k # 12,
0 # l # 13
2.3. Crystallography
Number of re¯ections
Corrections applied
Computer programs
2414 with I . 3.0sꢀI)
Lorentz-polarization
SHELXS86 [17] MoIEN [18],
ORTEP [19]
The experimental data, methods and the procedures
used to elucidate the structure and other related para-
meters are given in Table 1. The structure was solved
by direct methods, SHELXS86 [17]. The positions of
H atoms were clari®ed from difference synthesis and
re®ned isotropically. The structure was re®ned by
MOIEN [18] and the molecular structure ꢀFig. 1)
was drawn by ORTEP [19].
Source of atomic scattering
factors
Int. Table for X-ray Cryst. Vol.
IV, 1976 [20]
Structure solution
Direct methods
Hydrogen atoms were obtained
from difference map and re®ned
isotropically
Treatment of hydrogen atoms
No. of parameters var.
140
w ˆ 1/[sF2 1 ꢀ0.02F)2]
Weight
GOF
R
2.4. Method of calculation
1.25
0.056
Theoretical calculations were carried out at the
restricted Hartree±Fock level ꢀRHF) using PM3 [21]
semi-empirical SCF-MO methods in the MOPAC 7.0
[22], implemented in the Intel Pentium II computer.
All calculations were carried out with the complete
geometry optimization at precise level, and the
Rw
0.072
Ê 23
ꢀD/s)max ꢀe A
ꢀD/s)min ꢀe A
)
0.57
20.25
Ê 23
)
Fig. 1. An ORTEP [19] drawing of the title compound with the atom-numbering scheme. The thermal ellipsoids are drawn at the 50%
probability level.

È
C. Unaleroglu et al. / Journal of Molecular Structure 570 22001) 91±95
Æ
93
Table 2
conformers located at minima were characterized by
the calculations of vibrational frequencies.
Atomic coordinates and equivalent displacement parameters with
e..s.d.'s in parentheses. ꢀanistropically re®ned atoms are given in the
form of isotropic equivalent displacement parameters de®ned as: ꢀ4/
3)[a2Bꢀ1,1) 1 b2Bꢀ2,2) 1 c2Bꢀ3,3) 1 abꢀcos g)Bꢀ1,2) 1
acꢀcos b)Bꢀ1,3) 1 bcꢀcos a)Bꢀ2,3)]
3. Results and discussion
Ê 2
3.1. Crystal structure analysis
Atom
x
y
Z
BꢀA )
O1
N1
0.9448ꢀ1)
0.5784ꢀ2)
1.0766ꢀ2)
0.8599ꢀ2)
0.8857ꢀ2)
0.7922ꢀ2)
0.6738ꢀ2)
0.6505ꢀ2)
0.7414ꢀ2)
0.5731ꢀ2)
0.4700ꢀ2)
1.124ꢀ2)
1.066ꢀ2)
1.142ꢀ2)
0.967ꢀ2)
0.810ꢀ1)
0.570ꢀ2)
0.725ꢀ2)
0.498ꢀ2)
0.437ꢀ2)
0.385ꢀ2)
20.0180ꢀ2)
0.0187ꢀ2)
0.0667ꢀ3)
20.0229ꢀ2)
0.0648ꢀ2)
0.0509ꢀ2)
20.0496ꢀ2)
20.1382ꢀ2)
20.1237ꢀ2)
20.0675ꢀ2)
20.0128ꢀ3)
0.067ꢀ2)
1.3253ꢀ1)
0.6873ꢀ1)
1.3620ꢀ2)
1.1914ꢀ2)
1.0911ꢀ2)
0.9584ꢀ2)
0.9241ꢀ2)
1.0268ꢀ2)
1.1591ꢀ2)
0.7836ꢀ2)
0.5532ꢀ2)
1.460ꢀ2)
1.332ꢀ2)
1.315ꢀ2)
1.112ꢀ1)
0.891ꢀ1)
1.001ꢀ2)
1.228ꢀ2)
0.769ꢀ2)
0.548ꢀ2)
0.537ꢀ2)
5.26ꢀ3)
5.53ꢀ4)
5.87ꢀ5)
4.23ꢀ3)
4.65ꢀ4)
4.67ꢀ4)
4.45ꢀ4)
5.43ꢀ4)
5.30ꢀ4)
5.00ꢀ4)
5.64ꢀ5)
5.7ꢀ4)a
8.5ꢀ6)a
7.5ꢀ5)a
4.9ꢀ4)a
4.7ꢀ4)a
5.9ꢀ4)a
6.8ꢀ5)a
8.2ꢀ5)a
8.5ꢀ6)a
9.1ꢀ6)a
Single crystal X-ray structure of the title compound
was reported to further corroborate the structure
assignments. The ®nal coordinates and equivalent
isotropic displacement parameters are given in Table
2. The molecular structure with the atom numbering
scheme is shown in Fig. 1. The bond lengths and
angles with torsion angles are given in Table 3. The
asymmetric unit contains only one-half molecule. As
a whole, the title molecule is0in the staggered confor-
C1
C2
C3
C4
C5
C6
C7
C8
C9
mation
[N1±C9±C90 ±N1 ˆ 2180.0ꢀ2)8].
The
H11
H12
H13
H31
H41
H61
H71
H81
H91
H92
0.165ꢀ3)
phenyl rings and the CyN imine bonds are slightly
deviated from co-planarity as supported by the N1±
0.033ꢀ2)
0.130ꢀ2)
0.109ꢀ2)
C8±C5±C6[173.1ꢀ2)8]
[27.6ꢀ3)8] torsion angles.
and
N1±C8±C5±C4
20.208ꢀ2)
20.176ꢀ2)
20.177ꢀ3)
20.139ꢀ3)
0.071ꢀ3)
3.2. Computational study
In order to de®ne the conformational ¯exibility of
the title compound, semi-empirical calculations using
Table 3
0
Ê
The bond lengths ꢀA) and angles ꢀ8) with some selected torsion angles ꢀ8). Symmetry code ꢀ ): 2x 1 1, 2y, 2z 1 1
O1±C1
O1±C2
N1±C8
N1±C9
C2±C3
C9±C90
1.422ꢀ2)
1.367ꢀ2)
1.250ꢀ2)
1.467ꢀ2)
1.379ꢀ3)
1.486ꢀ3)
C2±C7
C3±C4
C4±C5
C5±C6
C5±C8
C6±C7
1.383ꢀ2)
1.385ꢀ2)
1.379ꢀ2)
1.392ꢀ3)
1.474ꢀ2)
1.374ꢀ2)
C1±O1±C2
C8±N1±C9
O1±C2±C3
O1±C2±C7
C3±C2±C7
C2±C3±C4
N1±C9±C90
118.0ꢀ1)
C3±C4±C5
C4±C5±C6
C4±C5±C8
C6±C5±C8
C5±C6±C7
C2±C7±C6
N1±C8±C5
121.4ꢀ2)
117.3ꢀ2)
124.3ꢀ1)
115.7ꢀ2)
119.9ꢀ1)
119.5ꢀ2)
110.1ꢀ2)
118.2ꢀ1)
122.5ꢀ2)
119.3ꢀ2)
121.0ꢀ2)
120.0ꢀ2)
123.6ꢀ2)
C1±O1±C2±C3
C1±O1±C2±C7
C9±N1±C8±C5
O1±C2±C3±C4
C7±C2±C3±C4
O1±C2±C7±C6
C3±C2±C7±C6
C8±N1±C9±C90
27.7ꢀ3)
172.4ꢀ2)
2179.6ꢀ2)
2179.9ꢀ2)
0.0ꢀ3)
C2±C3±C4±C5
C3±C4±C5±C6
C3±C4±C5±C8
C4±C5±C6±C7
C8±C5±C6±C7
C4±C5±C8±N1
C6±C5±C8±N1
C5±C6±C7±C2
20.3ꢀ3)
20.3ꢀ3)
2179.6ꢀ2)
1.2ꢀ3)
2179.5ꢀ2)
27.6ꢀ3)
173.1ꢀ2)
21.5ꢀ3)
2179.3ꢀ2)
0.8ꢀ3)
2146.5ꢀ2)

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C. Unaleroglu et al. / Journal of Molecular Structure 570 22001) 91±95
Æ
94
Fig. 2. PM3 calculated conformation energy pro®le of the u[N10 ±C90 ±C9±N1] torsion Angle ꢀ8).
PM3 molecular method were carried out. The energy
pro®le, which was obtained from PM3 method ꢀFig.
2) as a function of u[N10 ±C90 ±C9±N1] shows three
minima at 60, 180 and 3008 and three maxima at 0,
120 and 2408. The maxima positions correspond to the
eclipsed conformations. The eclipsed conformation I
is approximately 3.85 kcal mol21 unstable than the
eclipsed conformations III and V. In addition to the
torsional strain in conformation I, the van der Waals
interactions between the lone pair electrons of
nitrogen atoms and also between the electrons of the
±NyC± double bonds, cause strong repulsions than
the other conformations. Minima points in the
diagram correspond to the energetically favored
gauche conformations for II and VI and anti confor-
mation for IV. The difference in energy between
eclipsed conformation I and the anti conformation
IV is 5.0 kcal mol21. The gauche conformations
have approximately 1.0 kcal mol21 more energy
than the anti conformation. Conformational calcula-
tion using PM3 method reveals that the most energe-
tically stable structure is the anti conformation. This
conformation is controlled by the [N10 ±C90 ±C9±N1]
torsion angle which is found as 1808 by calculation
and also by X-ray analysis. Calculated torsion angles
for u[N1±C8±C5±C6] and u[N1±C8±C5±C4] are
179.98 and 20.18, respectively. These torsion angles
indicate that the non-hydrogen phenyl and the conju-
gated imine group atoms lie in a plane. This planarity
is slightly deviated in the crystal structure with torsion
angles of 173.1ꢀ2)8 [u ꢀN1±C8±C5±C6)] and
27.6ꢀ3)8 [u ꢀN1±C8±C5±C4)]. As can be seen
from Tables 4±6, the calculated and experimental
values are in good agreement with the exceptions of
Table 4
Comparison of the bond lengths ꢀA)
Ê
X-ray analysis
PM3
O1±C1
O1±C2
N1±C8
N1±C9
C2±C3
C2±C7
C3±C4
C4±C5
C5±C6
C5±C8
C6±C7
1.422ꢀ2)
1.367ꢀ2)
1.250ꢀ2)
1.467ꢀ2)
1.379ꢀ3)
1.383ꢀ2)
1.385ꢀ2)
1.379ꢀ2)
1.392ꢀ3)
1.474ꢀ2)
1.374ꢀ2)
1.406
1.379
1.292
1.463
1.403
1.399
1.386
1.399
1.397
1.466
1.398

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C. Unaleroglu et al. / Journal of Molecular Structure 570 22001) 91±95
Æ
95
Table 5
Comparison of the bond angles ꢀ8)
are slightly deviated from planarity by X-ray analysis
and exactly planar by PM3 method.
X-ray analysis
PM3
C1±O1±C2
C8±N1±C9
O1±C2±C3
O1±C2±C7
C3±C2±C7
C2±C3±C4
C3±C4±C5
C4±C5±C6
C4±C5±C8
C6±C5±C8
C5±C6±C7
C2±C7±C6
N1±C8±C5
118.0ꢀ1)
117.3ꢀ2)
124.3ꢀ1)
115.7ꢀ2)
119.9ꢀ1)
119.5ꢀ2)
121.4ꢀ2)
118.2ꢀ1)
122.5ꢀ2)
119.3ꢀ2)
121.0ꢀ2)
120.0ꢀ2)
123.6ꢀ2)
117.5
121.7
125.4
114.1
120.5
119.5
120.5
119.4
122.4
118.3
120.9
119.2
121.7
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Comparison of the torsion angles ꢀ8)
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C1±O1±C2±C3
C1±O1±C2±C7
C9±N1±C8±C5
O1±C2±C3±C4
C7±C2±C3±C4
O1±C2±C7±C6
C3±C2±C7±C6
C2±C3±C4±C5
C3±C4±C5±C6
C3±C4±C5±C8
C4±C5±C6±C7
C8±C5±C6±C7
C4±C5±C8±N1
C6±C5±C8±N1
C5±C6±C7±C2
N10 ±C90 ±C9±N1
C90 ±C9±N1±C8
27.7ꢀ3)
172.4ꢀ2)
2179.6ꢀ2)
2179.9ꢀ2)
0.0ꢀ3)
È
È
,
20.1
2178.9
2179.9
0.0
C 51 ꢀ1995) 880.
È
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È
È
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È
,
2179.3ꢀ2)
0.8ꢀ3)
2179.9
0.0
25 ꢀ1995) 831.
È
[14] F. Ercan, S.G. Oztas, N. Ancin, T. Hokelek, M. Tuzun,
È È
È
20.3ꢀ3)
20.3ꢀ3)
0.0
0.0
È
D. UlkuÈ, J. Chem Cryst. 26 ꢀ1996) 243.
[15] M. Gavranic, B. Kaitner, E. Mestrovic, J. Chem. Cryst. 26
ꢀ1996) 23.
2179.6ꢀ2)
1.2ꢀ3)
2179.9
0.0
[16] G.K. Gomma, M.H. Wahdan, Mater. Chem. Phys. 39
ꢀ1995) 209.
2179.5ꢀ2)
27.6ꢀ3)
2179.9
20.1
179.9
0.0
[17] G.M. Sheldrick, Acta Cryst. A 46 ꢀ1990) 467.
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173.1ꢀ2)
21.5ꢀ2)
2180.0ꢀ2)
2146.5ꢀ2)
2180.0
2141.3
[19] C.K. Johnson, Ortep II, Report ORNL-5138.Oak Ridge
National Laboratory. TN, 1976.
C8±N1±C9 bond and C90 ±C9±N1±C8 torsion
angles.
In conclusion, the most stable molecular structure
for the compound is in the anti conformation as
con®rmed by X-ray structure analysis and computa-
tion. The phenyl rings and conjugated imine groups
[20] The International Tables for X-ray Crystallography, Vol. IV
from 1974 are published by the Kynoch Press, Birmingham,
England and now distributed by the Kluwer Academic
Publishers, Dordrecht, The Netherlands.
[21] J.J.P. Stewart, J. Comput. Chem. 10 ꢀ1989) 209.
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Bloomington, IN, USA.