Synthesis and crystal structures of two schiff bases of 2-(methylthio)aniline with halogenated salicylaldehydes

Article abstract of DOI:10.1007/s10870-009-9601-5

The crystal structures of the new compounds 5-bromo-N-[2-(methylthio)- phenyl]salicylaldimine (1), and 3,5-dichloro-N-[2-(methylthio)phenyl] salicylaldimine (2) were obtained by single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P2₁/c with a = 14.1479(14) A, b = 5.3058(3) A, c = 19.104(3) A; β = 106.218(10)°; and Z = 4. Compound 2 crystallizes in the triclinic space group P1 with a = 11.2249(10) A, b = 13.863(2) A, c = 13.9055(9) A; and α = 99.378(15)°, β = 102.866(7)°, γ = 91.375(11)°; and Z = 6. Details of the synthesis, structures, and spectroscopic properties of the new compounds are discussed.

Full text of DOI:10.1007/s10870-009-9601-5

J Chem Crystallogr (2010) 40:34–39
DOI 10.1007/s10870-009-9601-5
ORIGINAL PAPER
Synthesis and Crystal Structures of Two Schiff Bases
of 2-(Methylthio)aniline with Halogenated Salicylaldehydes
Christopher G. Hamaker Æ Oksana S. Maryashina Æ
Dana K. Daley Æ Andrew L. Wadler
Received: 30 January 2009 / Accepted: 1 August 2009 / Published online: 11 August 2009
Ó Springer Science+Business Media, LLC 2009
Abstract The crystal structures of the new compounds
5-bromo-N-[2-(methylthio)-phenyl]salicylaldimine (1), and
3,5-dichloro-N-[2-(methylthio)phenyl]salicylaldimine (2)
were obtained by single crystal X-ray diffraction. Compound
1 crystallizes in the monoclinic space group P21/c with
ease of synthesis and their ability to be readily varied both
sterically and electronically.
The chemistry of Schiff bases is very diverse. The ligands
can coordinate in anywhere from a monodentate [2] to a
nonadentate [3] fashion to a metal ion. Schiff bases and their
metal complexes have been studied for use as antibacterial
agents [4–6], antifungal agents [7, 8], antitumor drugs [9–11],
catalysts [12–14], and in coordination chemistry [15–18].
Although the binding ability of Schiff bases to metals
has been extensively studied, their interactions with each
other have not been studied as much. In Schiff base com-
pounds, the imine nitrogen can act as an inter- or intra-
molecular hydrogen-bond acceptor and the hydroxyl
oxygen in salicylaldehyde derivatives can act as an inter-
molecular hydrogen-bond acceptor. Hydrogen bonding
interactions are important because of their application in
the pharmaceutical industry. The type and strength of the
interactions between the molecules in the formulation can
affect the uptake of the medication in the body.
˚
a = 14.1479(14) A, b = 5.3058(3) A, c = 19.104(3) A;
˚
˚
b = 106.218(10)°; and Z = 4. Compound 2 crystallizes in
ꢀ
˚
the triclinic space group P1 with a = 11.2249(10) A,
˚
˚
b = 13.863(2) A, c = 13.9055(9) A; and a = 99.378(15)°,
b = 102.866(7)°, c = 91.375(11)°; and Z = 6. Details of
the synthesis, structures, and spectroscopic properties of the
new compounds are discussed.
Keywords Schiff base ꢀ X-ray structure ꢀ
Sulfur compounds ꢀ Hydrogen bonds
Introduction
In 1864, German chemist Hugo Schiff developed a new
class of organic compound [1]. This group of compounds,
imines, are often referred to as Schiff bases in his honor.
The preparation of these compounds is simple and elegant.
They are prepared by condensing a carbonyl compound
with an amine, generally in refluxing alcohol. Schiff bases
are often used as ligands in inorganic chemistry. The most
common examples of these ligands are prepared from
salicylaldehyde derivatives to form a Schiff base ligand.
These ligands have been studied extensively due to their
Our group is interested in the synthesis, structure, and
coordination chemistry of novel, mixed-donor Schiff base
ligands [19–25]. As a part of our ongoing studies into the
structure and utility of sulfur-containing Schiff base
ligands, we report the synthesis, spectral properties, and
crystal structures of the Schiff bases prepared from the
condensation of 2-(methylthio)aniline with two haloge-
nated salicylaldehyde derivatives.
Experimental
C. G. Hamaker (&) ꢀ O. S. Maryashina ꢀ
D. K. Daley ꢀ A. L. Wadler
General Experimental
Department of Chemistry, Illinois State University,
Campus Box 4160, Normal, IL 61790, USA
e-mail: chamaker@ilstu.edu
All chemicals were purchased from commercial sources
and used as received. 1H and 13C NMR spectra were
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J Chem Crystallogr (2010) 40:34–39
35
recorded in CD2Cl2 on a Varian Gemini 400 MHz NMR
spectrometer and recorded in ppm relative to residual
CHDCl2 in CD2Cl2 at 5.32 ppm for 1H and CD2Cl2 at
54.0 ppm for 13C. IR spectra were collected on a Perkin
Elmer Spectrum One FTIR equipped with a universal ATR
attachment. UV/visible spectra were recorded in CH2Cl2
solution on a Cary 5E spectrometer. Melting points are
uncorrected. Elemental analyses were obtained from the
School of Chemical Sciences Microanalysis Laboratory at
the University of Illinois at Urbana-Champaign.
J = 2.4 Hz); 7.30 (m, 2H, HAr); 7.25 (d, 1H, HAr,
J = 7.2 Hz); 7.20 (m, 2H, HAr,); 2.48 ppm (s, 3H, SCH3).
13C NMR: d 160.0, 156.2, 144.2, 136.2, 133.1, 130.4, 129.0,
125.9, 125.7, 123.8, 123.1, 121.1, 117.6, 15.2 ppm. Analysis
calc. (found) for C14H11Cl2NOS: C, 53.86 (53.41); H, 3.55
(3.39); N, 4.49 (4.36).
X-ray Crystallography General
Crystal and data collection parameters are given in Table 1.
Data for 1 and 2 were collected on a Bruker–Nonius CAD4/
Mach3 diffractometer equipped with an Oxford Cryostreams
Synthesis of Schiff Bases
˚
Cobra cryostat using Mo-Ka (k = 0.71073 A) radiation at
5-Bromo-N-[2-(methylthio)phenyl]salicylaldimine (1)
173(2) K. Data collection and cell refinement was performed
using CAD4 express [26]. Data reduction was carried out
using XCAD4 [27]. Unit cell parameters were obtained from
a least-squares refinement of 25 centered reflections. The
data were corrected for absorption through the use of
empirical psi-scans [28]. Solution and data analysis were
performed using the WinGX software package. The struc-
tures were solved by direct methods using SIR-92 [29] for
compound 1 and SIR-2004 [30] for compound 2. The
refinements were completed using the program SHELXL-97
[31]. Hydrogen atoms attached to carbon were assigned
positions based on the geometries of their attached carbons.
The hydroxyl hydrogens were assigned positions based on
the Fourier difference map.
A 100 mL roundbottom flask was charged with 60 mL of
ethanol, 1.5339 g (11.018 mmol) of 2-(methylthio)aniline,
and 2.0646 g (10.809 mmol) of 3,5-dichlorosalicylaldeyde.
The resulting mixture changed from yellow to orange in
color and was refluxed for 30 min. The mixture was cooled to
room temperature and the product allowed to crystallize at
-30 °C overnight. The precipitate was filtered off and
washed with diethyl ether to yield 3.076 g (91%) of 1 as an
orange solid. Single crystals of 1 suitable for X-ray diffrac-
tion were grown by solvent diffusion of hexanes (mixture of
all five isomers, Fischer Scientific) into a methylene chloride
solution of 1. MP: 107–108 °C. IR: 1611 cm–1 (C=N). UV/
vis; kmax(e): 272 nm (18800 M-1 cm-1), 368 nm (9200
1
M-1 cm-1). H NMR: d 13.13 (s, 1H, OH); 8.51 (s, 1H,
CH=N); 7.48 (d, 1H, HAr, J = 2.8 Hz); 7.43 (dd, 1H, HAr,
J = 8.8 and 2.4 Hz); 7.25 (m, 2H, HAr); 7.17 (d, 2H, HAr,
J = 4.0 Hz); 6.91 (d, 1H, HAr, J = 8.8 Hz); 2.46 ppm (s,
3H, SCH3). 13C NMR: d 160.6, 160.5, 144.9, 136.1, 135.8,
134.8, 128.4, 125.7, 125.3, 121.2, 119.7, 117.5, 118.8,
15.0 ppm. Analysis calc. (found) for C14H12BrNOS: C,
52.18 (52.24); H, 3.75 (3.60); N, 4.35 (4.20).
Results and Discussion
The compounds were prepared by refluxing equimolar
amounts of substituted salicylaldehyde and 2-(methyl-
thio)aniline in absolute ethanol (Fig. 1). Both compounds
were isolated as orange solids in better than 90% yield.
IR and UV/vis Spectroscopy
3,5-Dichloro-N-[2-(methylthio)phenyl]salicylaldimine (2)
Both of the compounds have a strong absorbance at
1611 cm-1 in the infrared, confirming the presence of the
imine moiety. Additionally, both 1 and 2 have similar UV/
vis spectra in methylene chloride solution; both compounds
have strong absorptions near 270 and 370 nm.
A 100 mL roundbottom flask was charged with 30 mL of
ethanol, 1.4250 g (10.236 mmol) of 2-(methylthio)aniline,
and 1.9790 g (9.845 mmol) of 5-bromosalicylaldeyde. The
resulting mixture was refluxed for 60 min and cooled to
room temperature. The mixture was moved into a freezer at
-30 °C and theproduct was allowed to crystallizeovernight.
The precipitate was filtered off and washed with diethyl ether
to yield 2.957 g (93%) of 2 as an orange solid. Single crystals
of 2 suitable for X-ray diffraction were grown by solvent
diffusion of hexanes (mixture of all five isomers, Fischer
Scientific) into a methylene chloride solution of 2. MP: 116–
117 °C. IR: 1611 cm–1 (C=N). UV/vis; kmax(e): 273 nm
(18000 M-1 cm-1), 370 nm (8470 M-1 cm-1). 1H NMR: d
13.91 (s, 1H, OH); 8.56 (s, 1H, CH=N); 7.43 (d, 1H, HAr,
1H NMR Spectroscopy
Both compounds have simple and similar 1H NMR spectra
in CD2Cl2 solution. The SCH3 resonance is at 2.46 and
2.48 ppm in 1 and 2, respectively. The N=CH resonance
for both compounds is also similar (8.51 ppm in 1 and
8.56 ppm in 2). Both compounds exhibit sharp OH reso-
nances, indicative of strong intramolecular hydrogen
bonding, at 13.13 ppm in 1 and 13.91 ppm in 2.
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36
J Chem Crystallogr (2010) 40:34–39
Table 1 Summary of structure
determination of compounds 1
and 2
Compound
1
2
CCDC entry no.
Empirical formula
Formula weight
Color and habit
Crystal size (mm)
Temperature (K)
Space group
703374
703375
C14H12BrNOS
C14H11Cl2NOS
312.20
322.22
Yellow needle
Orange block
0.45 9 0.45 9 0.35
173(2)
0.42 9 0.25 9 0.18
173(2)
ꢀ
P1
P21/c
˚
a (A)
14.1479(14)
11.2249(10)
13.863(2)
˚
b (A)
5.0358(3)
˚
c (A)
19.104(2)
13.9055(9)
99.378(15)
102.866(7)
91.376(11)
2077.2(4)
a (°)
b (°)
c (°)
90
106.218(10)
90
3
˚
V (A )
1306.9(2)
Z
4
6
Dcalc (Mg/m3)
Absorption coeff (mm-1
Absorpton correction
1.638
1.497
)
3.291
0.609
w-Scans
w-Scans
Max. and min. transmission
F(000)
0.5522 and 0.4038
648
0.8071 and 0.7444
960
R indices [I [ 2r(I)]
R indices (all data)
Goodness-of-fit on F2
R1 = 0.0284, wR2 = 0.0695
R1 = 0.0489, wR2 = 0.0761
1.048
R1 = 0.0325, wR2 = 0.0851
R1 = 0.0490, wR2 = 0.0947
1.048
-3
)
˚
Largest peak/hole (e A
0.548 and -0.385
0.405 and -0.441
asymmetric units for each are shown in Figs. 2 and 3,
respectively. Selected bond lengths and angles are given in
Tables 2 and 3. Compound 1 crystallizes in the monoclinic
space group P21/c with one molecule in the asymmetric
unit while compound 2 crystallizes in the triclinic space
ꢀ
group P1 with three independent molecules in the asym-
metric unit.
Compound 1 is non-planar, with a dihedral angle
between the two aromatic rings of 19.03(12)° (Fig. 2,
Table 4). The molecule is stabilized by an intramolecular
O1–H1ꢀꢀꢀN9 hydrogen bond (Table 5). There is, at best, a
very weak intramolecular O1–H1ꢀꢀꢀS16 interaction (the
˚
H1ꢀꢀꢀS16 distance is approximately 0.03 A less than the
sum of the van der Waal’s radii; the O1ꢀꢀꢀS16 distance is
longer than the sum of the van der Waal’s radii). This very
weak interaction explains why the dihedral angle between
the aromatic rings smaller than that of some related com-
pounds without O–HꢀꢀꢀS interactions [23–25], but the
molecule is non-planar. The bond lengths and angles
(Tables 2, 3) are similar to reported compounds [22–25].
There are no significant intermolecular interactions in 1
and the packing is a result van der Waal’s forces.
Fig. 1 Preparation and structure of compounds 1 and 2
Molecular Structures of 1 and 2
In compound 2 (Fig. 3), which has a Z0 of three, two of
the three independent molecules are nearly planar; mole-
cule a has a dihedral angle between the aromatic rings of
The molecular structures for compounds 1 and 2 were
determined by single crystal X-ray diffraction and the
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J Chem Crystallogr (2010) 40:34–39
37
˚
Table 2 Summary of selected bond distances (A) for compounds 1
and 2
Bond
Length in 1 Length in 2a Length in 2b Length in 2c
O1–C2
C7–C8
C8–N9
1.345(3)
1.450(3)
1.283(3)
1.346(2)
1.456(2)
1.283(2)
1.419(2)
1.7641(17)
1.7947(19)
1.343(2)
1.458(2)
1.282(2)
1.421(2)
1.7638(18)
1.799(2)
1.347(2)
1.457(2)
1.283(2)
1.423(2)
1.7611(18)
1.793(2)
N9–C10 1.417(3)
C15–S16 1.761(3)
S16–C17 1.801(3)
Table 3 Summary of selected bond angles (°) for compounds 1 and 2
Bond
Angle in 1 Angle in 2a Angle in 2b Angle in 2c
Fig. 2 The molecular structure of 1 showing the atom numbering
scheme. Displacement ellipsoids are drawn at the 50% probability
level. Hydrogen atoms are drawn as spheres of arbitrary size. Dashed
lines indicate intramolecular hydrogen bonds
C7–C8–N9
121.7(2) 120.65(15) 121.23(16) 120.73(15)
121.6(2) 124.13(15) 123.11(15) 119.96(14)
C8–N9–C10
C15–S16–C17 103.14(13) 103.55(9)
103.59(9)
103.26(10)
1.51(2)° while molecule b has a dihedral angle between the
aromatic rings of 4.24(2)°. An overlay of molecules a and
b, generated using the program Mercury [32], is shown in
Fig. 4 illustrating the similarity between the molecules.
Molecule c is non-planar with a dihedral angle between the
aromatic rings of 55.37(5)°, which can be seen in the
overlay of molecules a and c in Fig. 5. Molecules a and b
have strong O1–H1ꢀꢀꢀN9 and O1–H1ꢀꢀꢀS16 hydrogen bonds
while molecule c has only a strong O1–H1ꢀꢀꢀN9 hydrogen
bond (Table 6). The bond angles and distances in 2
(Tables 2, 3) are in agreement with similar compounds
[22–25]. The packing in 2 is held together by a C–HꢀꢀꢀO
Table 4 Dihedral angle between phenyl rings C2–C7 and C10–C15
(°) for compounds 1 and 2
Angle in 1
Angle in 2a
Angle in 2b
Angle in 2c
14.03(12)
1.51(2)
4.24(2)
55.37(5)
˚
Table 5 Intramolecular hydrogen-bond geometry (A, °) in com-
pound 1
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
DꢀꢀꢀA
D–HꢀꢀꢀA
O1–H1ꢀꢀꢀN9
0.80(4)
1.93(4)
2.652(3)
150(4)
Fig. 3 The molecular structure
of the asymmetric unit of 2
showing the full atom
numbering scheme for molecule
c and partial atom numbering
schemes for molecules a and b
(all three molecules have the
same numbering scheme).
Displacement ellipsoids are
drawn at the 50% probability
level. Hydrogen atoms are
drawn as spheres of arbitrary
size. Dashed lines indicate
intramolecular hydrogen bonds
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J Chem Crystallogr (2010) 40:34–39
˚
Table 7 Intermolecular interactions (A, °) in compound 2
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
DꢀꢀꢀA
D–HꢀꢀꢀA
C8c–H8cꢀꢀꢀO1ai
0.95
0.95
2.44
2.90
3.339(2)
3.84
158
170
C6b–H6bꢀꢀꢀCg(6)ii
Fig. 4 Overlay of molecules a and b of compound 2 generated using
the program Mercury
DꢀꢀꢀA
DꢀꢀꢀA
Cl5aꢀꢀꢀCl5aiii
3.3618(10)
(i) -x ? 1, -y ? 1, -z; (ii) x, y, z - 1; (iii) -x ? 1, -y ? 1,
-z ? 1; Cg(6) is the center of gravity of ring C10c–C11c–C12c–
C13c–C14c–C15c
Fig. 5 Overlay of molecules a and c of compound 2 generated using
the program Mercury
˚
Table 6 Intramolecular hydrogen-bond geometry (A, °) in com-
pound 2
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
DꢀꢀꢀA
D–HꢀꢀꢀA
O1a–H1aꢀꢀꢀN9a
O1a–H1aꢀꢀꢀS16a
O1b–H1bꢀꢀꢀN9b
O1b–H1bꢀꢀꢀS16b
O1c–H1cꢀꢀꢀN9c
0.83(3)
0.83(3)
0.90(3)
0.90(3)
0.83(3)
1.80(3)
2.73(3)
1.76(3)
2.77(3)
1.83(3)
2.567(2)
154(3)
131(3)
154(3)
130(3)
152(3)
3.3369(15)
2.597(2)
3.4135(14)
2.595(2)
hydrogen bond, a ClꢀꢀꢀCl interaction, and a C–Hꢀꢀꢀp inter-
action (Table 7). Additionally, there are weak p-p inter-
actions in 2 leading to the formation of p-stacks of
a and b molecules that run parallel to the b-axis (Fig. 6).
The distance between the interacting rings is Cg(1)ꢀꢀꢀ
i
Fig. 6 Packing diagram for compound 2, viewed down the a axis.
Dashed lines indicate intermolecular hydrogen-bonding and ClꢀꢀꢀCl
interactions
i
i
˚
˚
Cg(2) = 3.69 A; Cg(1)ꢀꢀꢀCg(4) = 3.73 A; Cg(2)ꢀꢀꢀCg(3)
iv
˚
˚
= 3.61 A; Cg(3)ꢀꢀꢀCg(4) = 4.02 A [Cg(1) is center of
gravity of ring C2a–C3a–C4a–C5a–C6a–C7a; Cg(2) is the
center of gravity of ring C10a–C11a–C12a–C13a–C14a–
C15a; Cg(3) is the center of gravity of ring C2b–C3b–C4b–
C5b–C6b–C7b; Cg(4) is the center of gravity of ring
C10b–C11b–C12b–C13b–C14b–C15b]; symmetry opera-
tions: i = -x ? 1, -y ? 1, -z; iv = -x ? 1, -y, -z].
There has been significant interest recently in structures
with Z0 [ 1 [33–36]. Of all of the structures published in
the Cambridge Structural Database, 8.8% of all structures
and 11.5% of all organic structures had Z0 [ 1 [36]. Steed
and co-workers have identified several types of intermo-
lecular interactions which, when combined with each other,
can lead to crystal structures with Z0 [ 1, due to what they
term ‘‘synthon frustration’’ [33]. Compound 2 has three of
the identified interactions, a ClꢀꢀꢀCl contact, a C–Hꢀꢀꢀp
contact, and p–p stacking. The presence of these three
interactions probably contributes to the unusual Z0 value of
3 in compound 2. Another potential factor in the unusual Z0
is the fact that one of the molecules has a significantly
shape than the other two molecules in the asymmetric unit.
In two related molecules [24, 25] without any hydroxyl
groups to form intramolecular hydrogen bonds, the mole-
cules deviate significantly from planarity. Also in agreement
with the current results, the compound 3-methoxy-N-[2-
(methylthio)phenyl]salicylaldimine has both O–HꢀꢀꢀN and
O–HꢀꢀꢀS intramolecular hydrogen bonds, and it is nearly
planar with a dihedral angle of 6.78(7)° between the aromatic
rings [22].
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J Chem Crystallogr (2010) 40:34–39
39
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Acta 360:523
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CCDC-703374 and CCDC-703375 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.
ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: ?44(0)1223-336033.
Acknowledgments CGH wishes to thank Illinois State University
for financial support (URG-FRA awards).
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