Synthesis, characterization, crystal structures and antibacterial activities of some Schiff bases with N2O2 donor sets

Article abstract of DOI:10.1007/s13738-018-1347-6

A series of Schiff base compounds were synthesized by the reaction of different 3,5-dihalosalicylaldehyde (halo atoms equal to Cl, Br and I) with polymethylenediamines of varying chain length. The Schiff bases were characterized using FT-IR, UV–Vis,

Full text of DOI:10.1007/s13738-018-1347-6

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1347-6
ORIGINAL PAPER
Synthesis, characterization, crystal structures and antibacterial
activities of some Schif bases with N2O2 donor sets
Amir Adabi Ardakani1 · Hadi Kargar1 · Nourollah Feizi1 · Muhammad Nawaz Tahir2
Received: 22 January 2018 / Accepted: 19 March 2018
© Iranian Chemical Society 2018
Abstract
A series of Schif base compounds were synthesized by the reaction of diferent 3,5-dihalosalicylaldehyde (halo atoms equal
to Cl, Br and I) with polymethylenediamines of varying chain length. The Schif bases were characterized using FT-IR,
UV–Vis, 1H NMR, 13C NMR and mass spectroscopic techniques, and elemental analyses (CHN), and crystal structure of
some compounds was determined by X-ray crystallography. The in vitro biological screening efects of the synthesized
compounds were tested against diferent microbial kinds. The results revealed that all compounds were biologically active.
Keywords Schif base · N2O2 donor sets · Crystal structure · Antibacterial activity
Introduction
[10–12], antifungal [13–15], anticancer [16], antituberular
[17, 18], antiviral [19], anti-infammatory [20, 21], anticon-
vulsant [22, 23], antimalarial [24] and antitumor [25] activ-
ity. Structure–activity relationship (SAR) of Schif bases
has been studied by a lot of researchers [26]. On the basis
of these studies, unsubstituted salicylaldehyde has only low
activity. In some cases, the efect of substituents is dramatic.
The presence of functional groups such as halogen, hydroxyl
or nitro may cause higher activity, but the efects are not
easily predictable nor can they be extrapolated from one
microbe to another [27, 28].
Compounds containing an azomethine group (–CH=N–)
are known as Schif bases. Their preparation, chemical and
physical properties have been studied by many research
groups. Schif bases have diferent applications in various
fields such as electrochemistry, bioinorganic, catalysis,
metallic deactivator, separation processes, organic syntheses
and environmental chemistry [1–4].
Due to the presence of donor atoms such as nitrogen,
oxygen and sulfur in Schif bases, these compounds are
structurally similar to biological systems. In recent years, a
considerable number of tetradentate salen-type Schif base
compounds, especially those have a N2O2 donor sets, can
be used as ligands to obtain metal complexes that can serve
as more or less successful models of biological compounds
[5–7] and as catalyst in organic reactions [8, 9]. These com-
pounds have been broadly examined for their antibacterial
In the current work, we synthesized nine new Schif bases
derived from various primary diamines and 3,5-dichlorosal-
icylaldehyde, 3,5-dibromosalicylaldehyde and 3,5-diiodos-
alicylaldehyde (Fig 1). The compounds were characterized
using FT-IR, UV–Vis, 1H NMR, 13C NMR, mass spectro-
scopic technique, elemental analyses (CHN) and single-
crystal X-ray difraction. The in vitro biological activities
of the compounds were evaluated against Staphylococcus
aureus, Bacillus cereus, Escherichia coli and Pseudomonas
aeruginosa.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-018-1347-6) contains
supplementary material, which is available to authorized users.
Experimental
* Hadi Kargar
h.kargar@pnu.ac.ir; hadi_kargar@yahoo.com
Materials and physical measurements
1
Department of Chemistry, Payame Noor University, PO
Box 19395-3697, Tehran, Islamic Republic of Iran
All chemicals were of reagent grade and used without fur-
2
Department of Physics, University of Sargodha, Sargodha,
ther purifcation. Melting points were determined in open
Punjab, Pakistan
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Fig. 1 Structural formula of the
Schif base compounds
capillaries and are uncorrected. The 1H (400 MHz) and 13
C
difraction experiments were obtained by slow evaporation
of the hot ethanolic solution of the compounds.
NMR (100 MHz) spectra were recorded at ambient tempera-
ture by a BRUKER AVANCE 400 MHz spectrometer using
CDCl3 as solvent. The chemical shift values (δ) are given
in ppm. Infrared spectra were recorded using KBr disks
on an FT-IR Prestige21 spectrophotometer in the range of
4000–400 cm−1. The mass spectra were obtained on an Agi-
lent Technologies 5975C instrument. The C, H and N micro-
analyses were obtained with a Thermo Finnigan Flash EA
1112 elemental analyzer. Electronic spectra were recorded
on a UV–Vis Cary 50 instrument. The X-ray data for the
compounds were collected at room temperature on a Bruker
Smart APEX CCD difractometer (Mo Kα = 0.71073 Å).
Full spheres of reciprocal lattice were scanned by 0.3° steps
in omega with a crystal-to-detector distance of 5 cm. Cell
refnement and data reduction were performed with the help
of the SAINT program [29]. Corrections for absorption were
made with the multiscan method and SADABS program
[29]. The structures were solved with direct methods using
SHELXS, and structure refnement on F2 was carried out
with the SHELXL-2014/7 program. All non-hydrogen atoms
were refned using anisotropic displacement parameters [30].
All calculations were done with PLATON [31].
6,6′((1E,1′E)(ethane1,2diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dichlorophenol) or csen was
prepared using ethane-1,2-diamine and 3,5-dichlorosal-
icylaldehyde: Yield 373.6 mg (92%). m.p.: 216 °C. UV–Vis
(λmax, nm): 429, 335, 262. IR (KBr): 3061m, 2912m, 2850m,
1635s, 1446s, 1362m, 1275m, 1207m, 1176m, 1042m,
1
854m, 731m, 696m, 563m, cm−1. H NMR (400 MHz,
CDCl3, δ): 13.99 (br, 2H, –OH), 8.31 (s, 2H, H–C=N), 7.43
(d, 2H, J = 2.4, H-6), 7.17 (d, 2H, J = 2.4, H-4), 4.03 (s,
4H, =N–CH2–C). 13C NMR (100 MHz, CDCl3, δ): 166.21,
157.79, 132.27, 129.85, 122.70, 121.55, 119.26, 57.70. MS
(m/z): calculated for [C16H12Cl4N2O2]+ 406.08, observed
406.0. Combustion analysis for C16H12Cl4N2O2: Calculated.
C 47.32, H 2.98, N 6.90; found C 47.21, H 2.92, N 6.25.
6,6′((1E,1′E)(propane1,3diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dichlorophenol) or cspn was
prepared using propane-1,3-diamine and 3,5-dichlorosal-
icylaldehyde: Yield 365.5 mg (87%). m.p.: 186 °C. UV–Vis
(λmax, nm): 429, 333, 262. IR (KBr): 3071m, 2947m, 2858m,
1631s, 1458s, 1363m, 1292m, 1219s, 1182s, 1066m,
1001m, 974m, 869m, 731m, 569m, 482m, cm−1. 1H NMR
(400 MHz, CDCl3, δ): 14.37 (br, 2H, –OH), 8.34 (s, 2H,
H–C=N), 7.44 (d, 2H, J = 2.4, H-6), 7.18 (d, 2H, J = 2.4,
H-4), 3.81 (t, 4H, J=6.4, =N–CH2–C), 2.17 (q, 2H, J=6.4,
=N–C–CH2). 13C NMR (100 MHz, CDCl3, δ): 164.44,
157.37, 131.93, 129.04, 122.55, 121.61, 118.87, 55.02,
30.82. MS (m/z): calculated for [C17H14Cl4N2O2]+ 420.11,
observed 420.0. Combustion analysis for C17H14Cl4N2O2:
Calculated. C 48.60, H 3.36, N 6.67; found C 48.83, H 3.28,
N 6.76.
General procedure for the synthesis of Schif bases
To a stirred ethanolic (25 mL) solution of 3,5-dihalosalicyla-
ldehyde (2 mmol) was added an ethanolic (25 mL) solution
of the diamine (1 mmol). The reaction mixture was refuxed
for 1–3 h at 80–90 °C in a water bath. The resulting solu-
tion was cooled to room temperature, and the resulting pre-
cipitate was collected by suction fltration and washed with
cold ethanol (3×10 mL) to aford the desired Schif base.
Single crystals of the isen, bspn and isbn suitable for X-ray
6,6′((1E,1′E)(butane1,4diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dichlorophenol) or csbn was
prepared using ethane-1,2-diamine and 3,5-dibromosal-
icylaldehyde: Yield 356.0 mg (82%). m.p.: 216 °C. UV–Vis
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Journal of the Iranian Chemical Society
(λmax, nm): 428, 334, 264. IR (KBr): 3068m, 2914m, 2852m,
1636s, 1462s, 1355m, 1288, 1211m, 1161m, 1035m, 957m,
740m, 686m, 555m, cm−1. 1H NMR (400 MHz, CDCl3, δ):
14.58 (br, 2H, –OH), 8.28 (s, 2H, H–C=N), 7.43 (d, 2H,
J=2.4, H-6), 7.16 (d, 2H, J=2.4, H-4), 3.71 (t, 4H, J=6.0,
=N–CH2–C), 1.85 (q, 2H, J=6.0, =N–C–CH2). 13C NMR
(100 MHz, CDCl3, δ): 167.34, 157.65, 134.54, 129.48,
127.34, 119.48, 117.65, 53.34, 27.34. MS (m/z): calculated
for [C18H16Cl4N2O2]+ 434.14, observed 434.0. Combustion
analysis for C18H16Cl4N2O2: Calculated. C 49.80, H 3.71, N
6.45; found C 49.98, H 3.66, N 6.43.
=N–CH2–C), 1.85 (q, 2H, J= 6.0, =N–C–CH2). 13C NMR
(100 MHz, CDCl3, δ): 165.92, 164.89, 138.52, 134.54,
117.77, 115.90, 104.22, 53.46, 27.34. MS (m/z): calculated
for [C18H16Br4N2O2]+ 611.95, observed 611.9. Combus-
tion analysis for C18H16Br4N2O2: Calculated. C 55.33, H
2.67, N 4.58; found C 54.97, H 2.61, N 4.47.
6,6′((1E,1′E)(ethane1,2diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-diiodophenol) or isen
was prepared using ethane-1,2-diamine and 3,5-diiodo-
salicylaldehyde: Yield 578.9 mg (75%). m.p.: 236 °C.
UV–Vis (λmax, nm): 439, 343, 260. IR (KBr): 3053m,
2881m, 1630s, 1580m, 1458m, 1437s, 1352m, 1285m,
1209m, 1153m, 1032m, 966m, 868m, 741m, 552m, cm−1.
1H NMR (400 MHz, CDCl3, δ): 14.49 (br, 2H, –OH),
8.48 (s, 2H, H–C=N), 8.04 (d, 2H, J = 2.0, H-6), 7.72 (d,
2H, J = 2.0, H-4), 4.01 (s, 4H, =N–CH2–C). 13C NMR
(100 MHz, CDCl3, δ): 166.66, 164.66, 148.99, 141.15,
118.73, 92.51, 77.69, 55.43. MS (m/z): calculated for
[C16H12I4N2O2]+ 771.90, observed 771.9. Combustion
analysis for C16H12I4N2O2: Calculated. C 24.90, H 1.57,
N 3.63; found C 24.99, H 1.69, N 3.55.
6,6′((1E,1′E)(ethane1,2diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dibromophenol) or bsen was
prepared using ethane-1,2-diamine and 3,5-dibromosal-
icylaldehyde: Yield 467.1 mg (80%). m.p.: 238 °C. UV–Vis
(λmax, nm): 431, 335, 264. IR (KBr): 3099m, 3054m, 2939m,
1623s, 1596m, 1531m, 1508m, 1434m, 1251s, 978m, 854m,
1
822m, 748m, 569m, 513w, cm−1. H NMR (400 MHz,
CDCl3, δ): 14.15 (br, 2H, –OH), 8.27 (s, 2H, H–C=N), 7.72
(d, 2H, J = 2.4, H-6), 7.34 (d, 2H, J = 2.4, H-4), 4.00 (s,
4H, =N–CH2–C). 13C NMR (100 MHz, CDCl3, δ): 166.84,
162.02, 138.23, 134.33, 118.90, 114.34, 106.60, 55.60. MS
(m/z): calculated for [C16H12Br4N2O2]+ 583.90, observed
583.80. Combustion analysis for C16H12Br4N2O2: Calcu-
lated. C 32.91, H 2.07, N 4.80; found C 32.21, H 1.99, N
4.50.
6,6′((1E,1′E)(propane1,3diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-diiodophenol) or ispn was
prepared using propane-1,3-diamine and 3,5-diiodos-
alicylaldehyde: Yield 534.4 mg (68%). m.p.: 176 °C.
UV–Vis (λmax, nm): 437, 343, 258. IR (KBr): 3049m,
2292m, 2851m, 1624s, 1582m, 1456m, 1435s, 1357m,
1319m, 1285m, 1271m, 1215m, 1155s, 1095m, 1060m,
987m, 964m, 871m, 850m, 738m, 657m, 547m, cm−1. 1H
NMR (400 MHz, CDCl3, δ): 14.40 (br, 2H, –OH), 8.19
(s, 2H, H–C=N), 8.08 (d, 2H, J = 2.0, H-6), 7.52 (d, 2H,
J = 2.0, H-4), 3.79 (t, 4H, J = 6.4, =N–CH2–C), 2.16 (q,
2H, J = 6.4, =N–C–CH2). 13C NMR (100 MHz, CDCl3,
δ): 166.07, 165.94, 149.01, 141.26, 118.21, 93.76, 76.33,
52.19, 30.52. MS (m/z): calculated for [C17H14I4N2O2]+
785.93, observed 785.90. Combustion analysis for
C17H14I4N2O2: Calculated. C 25.98, H 1.80, N 3.56; found
C 26.09, H 1.91, N 3.45.
6,6′((1E,1′E)(propane1,3diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dibromophenol) or bspn was
prepared using propane-1,3-diamine and 3,5-dibromosal-
icylaldehyde: Yield 466.4 mg (78%). m.p.: 160 °C. UV–Vis
(λmax, nm): 430, 335, 259. IR (KBr): 3064m, 2943m, 2850m,
1632s, 1560m, 1514m, 1444s, 1360m, 1286m, 1221m,
1167m, 1067m, 1036m, 999m, 872w, 849m, 740m, 687m,
561w, 474w, 419w, cm−1. 1H NMR (400 MHz, CDCl3, δ):
14.52 (br, 2H, –OH), 8.29 (s, 2H, H–C=N), 7.73 (d, 2H,
J=2.4, H-6), 7.33 (d, 2H, J=2.4, H-4), 3.79 (t, 4H, J=6.4,
=N–CH2–C), 2.16 (q, 2H, J=6.4, =N–C–CH2). 13C NMR
(100 MHz, CDCl3, δ): 166.16, 163.53, 138.28, 134.38,
118.53, 115.17, 105.41, 52.35, 30.51. MS (m/z): calculated
for [C17H14Br4N2O2]+ 597.93, observed 597.90. Combustion
analysis for C17H14Br4N2O2: Calculated. C 34.15, H 2.36, N
4.69; found C 34.04, H 2.28, N 4.57.
6,6′((1E,1′E)(butane1,4diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-diiodophenol) or isbn was
prepared using butane-1,4-diamine and 3,5-dibromo-
salicylaldehyde: Yield 480.0 mg (60%). m.p.: 196 °C.
UV–Vis (λmax, nm): 434, 343, 261. IR (KBr): 3053w,
2940m, 2856w, 1634s, 1580m, 1477m, 1439m, 1352m,
1219m, 1182m, 1128m, 1041m, 1016m, 912m, 866m,
759m, 657m, cm−1. 1H NMR (400 MHz, CDCl3, δ): 14.72
(br, 2H, –OH), 8.13 (s, 2H, H–C=N), 8.06 (d, 2H, J = 2.0,
H-6), 7.50 (d, 2H, J = 2.0, H-4), 3.69 (t, 4H, J = 6.8,
=N–CH2–C), 1.83 (q, 2H, J= 6.8, =N–C–CH2). 13C NMR
(100 MHz, CDCl3, δ): 167.24, 165.66, 149.19, 141.45,
117.68, 94.88, 75.39, 53.40, 27.37. MS (m/z): calculated
for [C18H16I4N2O2]+ 799.96, observed 799.9. Combustion
6,6′((1E,1′E)(butane1,4diylbis(azanylylidene))
bis(methanylylidene))bis(2,4-dibromophenol) or bsbn
was prepared using butane-1,4-diamine and 3,5-dibro-
mosalicylaldehyde: Yield 428.4 mg (70%). m.p.: 207 °C.
UV–Vis (λmax, nm): 429, 336, 261. IR (KBr): 3064m,
2945m, 2916m, 2846m, 1632s, 1560m, 1514m, 1452s,
1366m, 1286m, 1196m, 1163m, 1043m, 874m, 686m,
1
474w, cm−1. H NMR (400 MHz, CDCl3, δ): 14.74 (br,
2H, –OH), 8.24 (s, 2H, H–C=N), 7.72 (d, 2H, J = 2.4,
H-6), 7.34 (d, 2H, J = 2.4, H-4), 3.71 (t, 4H, J = 6.0,
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Journal of the Iranian Chemical Society
analysis for C18H16I4N2O2: Calculated. C 27.03, H 2.02, N
3.50; found C 27.14, H 2.03, N 3.63.
FT‑IR spectra
The infrared spectrum provided valuable information for
identifying the nature of the functional groups. For exam-
ple, FT-IR spectrum of csen is shown in Fig. 2. The IR
spectra of the Schif bases show strong intensity absorp-
tion bands at 1623–1636 cm−1 assigned to C=N stretching
mode of the azomethine [32]. The presence of aromatic
rings has been identifed by their characteristic ring vibra-
tions at 1500–1400, 1100–1050 and 900–700 cm−1 regions
[33–35]. In all compounds, the absence of characteristic
bands of unreacted carbonyl groups ν(C=O) and primary
amine ν(NH2) confrms the formation of the proposed Schif
base structure. A band in the 1250–1290 cm−1 due to C–O
phenolic group was also observed in these compounds [36].
Biological activity evaluation
The in vitro antibacterial activity of the synthesized Schif
bases was investigated against the standard strains of two
Gram-positive (Staphylococcus aureus PTCC1431, Bacillus
cereus PTCC1015) and two Gram-negative (Escherichia coli
PTCC1394, Pseudomonas aeruginosa PTCC1074) bacte-
ria. In order to compare the results, ampicillin (10 mg/disk)
and erythromycin (15 mg/disk) were used as standard anti-
bacterial drugs. The compounds were dissolved in DMSO
at 50 μg mL−1 concentration. Bacteria culture Petri dishes
treated with the test compounds were incubated for 24 h at
37 °C. Inhibition zone (mm) around the specimens was used
to indicate antibacterial activity of each of compounds. Each
test was performed in triplicate.
UV–Vis spectra
The UV–visible absorption spectra were obtained in DMSO
(10−4 M) at room temperature. Earlier papers emphasis that
the electronic absorption bands of the salicylaldehyde-type
Schif base comprise of three bands [37]. The compounds
exhibit three main peaks in the about 261, 337 and 432 nm.
The 250–300 nm bands are due to the π→π* transitions of
the aromatic rings. It is shown in Fig. 3. The bands at the
300–350 nm range involve π→ π* transitions of the C=N
chromophore group. The longer wavelength bands over ca.
Results and discussion
All the Schif base compounds are stable at room tempera-
ture and are non-hygroscopic. The compounds are insoluble
in water, ethanol and methanol but are soluble in DMSO.
100
%T
90
80
70
60
50
40
30
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
Fig. 2 FTIR spectrum of csen
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Journal of the Iranian Chemical Society
NMR spectra
1
The H NMR spectra of the Schif base compounds were
obtained in CDCl3 at room temperature. The synthesized
compounds showed signals of all protons in their expected
regions, and the integration curve were equivalent to the
total number of the protons deduced from their proposed
structure. The chemical shift for the OH protons in the
Schif base compounds is observed in 13.99–14.74 ppm.
The signals at δ = 8.13–8.48 ppm are assigned to the
–C(H)=N– proton of azomethine [40, 41]. It is known
that orthophenolic hydrogen bonding shifts the resonance
signal of a proton to lower feld (higher frequency). Com-
paring the 1H NMR data of the OH protons of salicyl part
of the compounds, it can be said that the strongest intra-
molecular hydrogen bond (OH···N) is formed in bsbn, and
the weakest one in csen. It is interesting that 13.99 ppm
value of the csen is lower than those of the other phenolic
Schif bases. This diference means that the phenolic OH
proton of csen has less acidic character and, consequently,
csen has weaker intramolecular hydrogen bonding accord-
ing to the others. The aromatic protons of the Schif base
Fig. 3 UV–Vis. spectrum of csen
400 nm can be assigned to the intramolecular charge transfer
interactions (n→π* transition) of the non-bonding electrons
present on the nitrogen of the azomethine group in the Schif
base compounds [38, 39].
Fig. 4 1H NMR spectrum of csen in CDCl3
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Journal of the Iranian Chemical Society
Fig. 5 13C NMR spectrum of csen in CDCl3
compounds appeared at δ=7.16–8.08 ppm. The H-4 signal
was observed as a doublet, due to coupling with the H-6,
and also the H-6 signal was observed as a doublet, due
to coupling with the H-4. The multiples of the aliphatic
protons were appeared within the range of 1.83–4.03 ppm.
The 13C NMR spectra of the Schif base compounds are
consistent with the number of carbons in their structures.
The peaks observed at 166.22, 167.35, 164.44, 166.85,
166.17, 165.93, 166.66, 166.07 and 167.24 ppm are ascribed
to the imine carbon atoms of csen, cspn, csbn, bsen, bspn,
bsbn, isen, ispn and isbn, respectively. The existence of
these peaks in the spectra of Schif base compounds supports
the presence of the Schif base in them.
Mass Spectra
The formulation of the Schif base compounds is deduced
from analytical data, H and 13C NMR and further sup-
1
ported by mass spectroscopy. The electron impact mass
spectra of Schif base compounds are recorded and inves-
tigated at 70 eV of electron energy. The mass spectra of
the studied Schif bases are characterized by low to high
relative intensity molecular ion peaks. The mass spec-
tra of the compounds showed molecular ion peaks at m/e
404, 418, 432, 580, 594, 608, 772, 786 and 800 which
corresponding to their molecular formula C16H12Cl4N2O2
(csen), C17H14Cl4N2O2 (cspn), C18H16Cl4N2O2 (csbn),
C16H12Br4N2O2 (bsen), C17H14Br4N2O2 (bspn),
C18H16Br4N2O2 (bsbn), C16H12I4N2O2 (isen), C17H14I4N2O2
(ispn) and C18H16I4N2O2 (isbn), respectively. It is obvious
that the molecular ion peaks are in good agreement with
their suggested empirical formula as indicated from elemen-
tal analyses (Table 1). The low intensities of the molecular
The chemical shift values of the diferent types of pro-
tons and carbons in the csen are reported in Figs. 4 and 5,
respectively.
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Journal of the Iranian Chemical Society
Table 1 Crystal data and
refnement parameters for isbn,
bspn and isen
Schif base compound
isbn
bspn
isen
Empirical formula
Formula weight
Crystal size (mm)
Temperature (K)
Crystal system
Space group
C18H16I4N2O2
799.93
0.300×0.140×0.120
296 (2)
Monoclinic
P21
C17H14Br4N2O2
597.94
0.350×0.250×0.220
296 (2)
Orthorhombic
Fdd2
C16H10I4N2O2
769.86
0.250×0.150×0.160
296 (2)
Monoclinic
P21/c
θ range for data collection (°) 1.336–25.997
2.010–25.992
25.8874 (17)
32.562 (2)
4.4186 (3)
90
1.574–27.976
13.0382 (19)
10.6131 (16)
7.0982 (10)
90
a (Å)
b (Å)
c (Å)
α (°)
7.5152 (8)
9.3943 (11)
15.6191 (17)
90
β (°)
102.663 (4)
90
1075.9 (2)
2
2.469
5.808
90
90
97.067
90
974.8 (2)
2
2.623
6.405
696
γ (°)
V (Å3)
Z
3724.7 (4)
8
2.133
8.658
2288
ρcalc (Mg/m3)
μ (mm−1
F(000)
)
732
Index ranges
−9≤h≤9
−11≤k≤9
−19≤l≤19
8871
−31≤h≤31
−40≤k≤40
−5≤l≤5
7643
−17≤h≤17
−13≤k≤13
−9≤l≤9
2316
Refections collected
Independent refections
Data/restraints/parameters
Goodness-of-ft (GOF)
Final R indices [I>2σ(I)]
3610 [R(int)=0.0421] 1792 [R(int)=0.0409] 2316 [R(int)=0.05]
3610/1/236
0.985
1792/1/116
1.037
R1 =0.0265
wR2 =0.0555
R1 =0.0384
wR2 =0.0588
2316/0/110
1.090
R1 =0.0692
wR2 =0.2577
R1 =0.0865
wR2 =0.2731
R1 =0.0363
wR2 =0.0575
R1 =0.0607
wR2 =0.0658
Final R indexes (all data)
Fig. 6 Mass spectrum of csen
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Journal of the Iranian Chemical Society
Table 2 Selected bond lengths
(Å) and angles (°) of bspn, isbn
and isen
Bond
bspn
Bond
isbn
Bond
isen
Lengths (Ǻ)
N(1)–C(7)
N(1)–C(8)
O(1)–C(1)
Br(1)–C(2)
1.274 (7)
1.473 (7)
1.343 (6)
1.888 (5)
N(1)–C(7)
N(1)–C(8)
O(1)–C(1)
I(1)–C(2)
1.290 (14)
1.474 (12)
1.272 (13)
2.103 (11)
N(1)–C(7)
N(1)–C(8)
O(1)–C(1)
I(1)–C(4)
1.295 (17)
1.470 (15)
1.346 (14)
2.096 (12)
Angles (°)
C(7)–N(1)–C(8)
O(1)–C(1)–C(2)
C(1)–C(2)–Br(1)
N(1)–C(7)–C(6)
118.7 (5)
119.9 (5)
119.3 (4)
121.8 (5)
C(7)–N(1)–C(8)
O(1)–C(1)–C(2)
C(1)–C(2)–I(1)
N(1)–C(7)–C(6)
122.9 (10)
122.0 (11)
118.1 (9)
C(7)–N(1)–C(8)
O(1)–C(1)–C(2)
C(1)–C(2)–I(2)
N(1)–C(7)–C(6)
118.2 (12)
119.7 (11)
119.0 (9)
123.6 (11)
121.2 (12)
Fig. 7 ORTEP plots of bspn
(top), isen (middle) and isbn
(down) with atom numbering
and ellipsoids probability at
30%
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Journal of the Iranian Chemical Society
Table 3 Antibacterial activity (zone of inhibition, mm) of synthe-
sized Schif base compounds
the tested materials. The microorganisms used in this work
include Staphylococcus aureus and Bacillus cereus (as
Gram-positive bacteria) and Escherichia coli and Pseu-
domonas aeruginosa (as Gram-negative bacteria).
The antibacterial activities of the compounds are repre-
sented by size of the diameter of inhibition zone in mm and
for all Schif bases are shown in Table 3.
compound
E. coli
P. aeruginosa
S. aureus
B. cereus
csen
cspn
csbn
bsen
bspn
bsbn
isen
ispn
14
15
12
12
14
15
12
13
11
16
11
13
11
13
12
12
13
12
12
12
17
14
12
12
12
22
25
21
26
25
25
25
27
19
16
18
19
26
23
22
21
22
24
26
The compounds were tested at the concentrations of
50 μg mL−1 in DMSO. Antimicrobial activity depends on
the nature of bacterial strain, the solvent and chelating abil-
ity of the Schif base. It is believed that Schif bases act by
forming a chelate with the bacterial strain. This may involve
hydrogen bonding through the azomethine group with the
active centers of cell constituents thus resulting in an inter-
ference with normal cell process.
isbn
Erythromycin
Ampicillin
In general, compounds having chloro, bromo or iodo
substituent in their structure are having signifcant anti-
bacterial and antifungal activity. In all nine compounds,
the central ligand is salicylaldehyde with diferent side
chains. In csen, cspn and csbn, it is 3,5-dichloro, in bsen,
bspn and bsbn, it is 3,5-dibromo, and in isen, ispn and
isbn, it is 3,5-diiodo. The difusion capacity of the com-
pounds and the efect of them against bacteria vary with
their structure.
ion peaks in some of compounds, [M]+, are indicative of
the ease of fragmentation of these compounds, and this may
refect of halo atoms present in structures [42]. The mass
spectrum of csen is shown in Fig. 6.
Crystal structure description
The solid-state structures of isbn, bspn and isen were deter-
mined by X-ray difraction. The crystal data and refne-
ment parameters are summarized in Table 1, and ORTEP
plots of isbn, bspn and isen are shown in Fig. 1. Selected
bond lengths and angles are summarized in Table 2. The
asymmetric unit of isbn comprises a potentially tetraden-
tate Schif base ligand. Pair of the intramolecular O–H…N
hydrogen bonds make S(6) ring. The compound crystallizes
in monoclinic system with P2(1) space group. The abso-
lute structure parameter (Flack parameter) was determined
successfully. The crystal packing of the compound shows
two-dimensional network of connected molecules through
the intermolecular C–I…π interactions parallel to ab-plane
(Fig. 7). The asymmetric unit of bspn comprises half of a
potentially tetradentate Schif base ligand. Pair of the intra-
molecular O–H…N hydrogen bonds make S(6) ring. The
intermolecular C–H…O interactions link neighboring mole-
cules along the a-axis. Similar to bspn compound, the asym-
metric unit of the isen compound comprises half of a poten-
tially tetradentate Schif base ligand. The crystal is twinned
non-merohedrally with a refned ration of 0.829(7)/0.171(7).
It is observed that the compounds with Br and I substitu-
ents have better antimicrobial activity according to the oth-
ers (as reported in previous articles [43, 44]).
It is evident from Table 3 that all Schif bases described
here were found to be biologically active and showed signif-
cantly enhanced antibacterial activity against all of the bac-
terial species. From the bactericidal activity, it is apparent
that the compounds were more toxic toward Gram-positive
strains than Gram-negative strains. This diference may be
attributed to the fact that the cell wall in Gram-positive bac-
teria is of a single layer, whereas the Gram-negative cell wall
is a multilayered structure.
For E. coli, the cspn and bsbn showed maximum activ-
ity followed by csen and bspn. Against P. aeruginosa, csen
and csbn showed maximum activity, and minimum inhi-
bition was observed for cspn. For S. aureus, isen showed
maximum inhibition. The bspn showed excellent activity
against B. cereus.
Conclusion
Antimicrobial activity
In this paper, a series of symmetrical Schif bases con-
taining the N2O2 unit derived from condensation reaction
of various diaminoalkyls with substituted salicylalde-
hydes have been synthesized. These compounds physi-
cally and chemically characterized through elemental
analysis (CHN), FT-IR, UV–Vis, 1H NMR, 13C NMR and
mass spectroscopic. The crystal structures of isen, bspn
The in vitro antibacterial activities of the synthesized Schif
base compounds and known drugs such as ampicillin and
erythromycin were screened in DMSO against more than
medically important Gram-positive and Gram-negative
bacteria to increase the chance of antibiotic principles in
1 3

Journal of the Iranian Chemical Society
15. H. Khanmohammadi, M. Salehifard, M.H. Abnosi, J. Iran. Chem.
Soc. 6, 300 (2009)
and isbn were determined by X-ray difraction at room
temperature. They have been crystallized in monoclinic,
orthorhombic and monoclinic, respectively. The antimicro-
bial activity results showed that most of the synthesized
Schif base compounds possess a good antibacterial activ-
ity against both Gram-negative and Gram-positive bacte-
ria tested. The structures of the Schif bases determine an
intensifcation of the antimicrobial activity.
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Crystallographic data have been deposited at the Cam-
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1563978 and 1563979 and contain the supplementary
crystallographic data for bspn, isen and isbn. These data
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ac.uk/conts/retrieving. html or from the CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK; Fax: (+44) 01223-336-
033; E-mail: deposit@ ccdc.cam.ac.
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