Synthesis, Characterization, and Biological Activity of the Schiff Base and Its Ni(II), Cu(II), and Zn(II) Complexes Derived from 4-(Dimethylamino)benzaldehyde and S-Benzyldithiocarbazate

Article abstract of DOI:10.1134/S107036321906015X

A Schiff base containing the nitrogen-sulfur donor chain [(CH₃)₂N-C₆H₄-CH=N-NH-C(S)-SCH2C6H5] was prepared by the condensation of 4-(dimethylamino)benzaldehyde and S-benzyldithiocarbazate and coordinated with Ni

Full text of DOI:10.1134/S107036321906015X

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 6, pp. 1197–1201. © Pleiades Publishing, Ltd., 2019.
Synthesis, Characterization, and Biological Activity
of the Schiff Base and Its Ni(II), Cu(II), and Zn(II) Complexes
Derived from 4-(Dimethylamino)benzaldehyde
and S-Benzyldithiocarbazate1
M. A. Latifa, Tania Tofaza, B. M. Chakia, H. M. Tariqul Islama,
Md. Saddam Hossaina, and Md. Kudrat-E-Zahanb*
a Department of Chemistry, Faculty of Science, Begum Rokeya University, Rangpur, 5400 Bangladesh
b Department of Chemistry, Faculty of Science, Rajshahi University, Rajshahi, 6500 Bangladesh
*e-mail: kudrat.chem@ru.ac.bd
Received April 6, 2018; revised June 15, 2019; accepted June 20, 2019
Abstract—A Schiff base containing the nitrogen−sulfur donor chain [(CH3)2N–C6H4–CH=N–NH–C(S)–
SCH2C6H5] was prepared by the condensation of 4-(dimethylamino)benzaldehyde and S-benzyldithiocarbazate
and coordinated with Ni(II), Cu(II), and Zn(II). The Schiff base and its metal complexes were characterized by
elemental analysis, IR, 1H and 13C NMR, electronic absorption spectroscopy and some of their physicochemical
properties were determined. The Schiff bases behaved as a bidentate uninegative ligand in all the complexes,
giving square-planar geometrical structures with Ni(II) and Cu(II) and a tetrahedral structure with Zn(II). The
Schiff base and its complexes were screened for antibacterial activity. The biological activity testing results
showed that the complexes were more potent antibiotics than the free ligand. The Cu(II) and Ni(II) complexes
displayed high antibacterial potency and Zn(II) was moderately active against bacteria.
Keywords: metal complexes, SBDTC, Schiff base, biological activity
DOI: 10.1134/S107036321906015X
INTRODUCTION
In this study, we synthesized a Schiff base and its
metal complexes, starting from 4-(dimethylamino)-
benzaldehyde. The ligand and it’s metal complexes
were tested for biological activity against pathogenic
and nonpathogenic bacteria.
Nitrogen–sulfur donor ligands, such as dithio-
carbazate (NH2NHCS2) and its substituted derivatives
continue to attract great interest of researchers, because
it has four potentially donor atoms, two of which are
sterically available for metal chelation [1–3].
Researchers in this area have synthesized new nitrogen–
sulfur donor ligands by the condensation of Schiff
bases with aldehydes and ketones [4–6]. The properties
of these ligands can be strongly modified by introduc-
ing organic substituents. The number of synthesized
ligands continues to increase because of the intriguing
observation that different ligands show different biolo-
gical properties, even though they may only slightly
differ in their molecular structure [7–10]. Transition
metal complexes of these ligands are also widely
studied due to their potential therapeutic use [11–14].
RESULTS AND DISCUSSION
The Schiff base, benzyl N'-(4-dimethylamino-
benzylidene)hydrazinecarbodithioate (SB), was syn-
thesized in high yield by the condensation of S-
benzyldithiocarbazate (SBDTC) with 4-(dimethyl-
amino)benzaldehyde in a neutral medium (Scheme 1).
The Ni(II), Cu(II), and Zn(II) complexes were
obtained by reacting the synthesized Schiff base with
the corresponding metal nitrates:
M(NO3)2·nH2O + SB → [ M(II)(SB)2],
where M(II) = Ni(II), Cu(II), Zn(II) and SB = benzyl
N'-(4-dimethylaminobenzylidene)hydrazinecarbodithioate.
1
Supplementary materials are available for this article at
https://doi.org/10.1134/S107036321906015X and are accessible
for authorized users.
As known, hydrazinecarbodithioic acid exists in
solutions as a mixture of the thione and thiol tautomers
1197

1198
LATIF et al.
Scheme 1.
S
H
HC N N
CHO
(1) Ethanol
(2) Reflux
SCH2C6H5
S
H
H2N N
+
SCH2C6H5
N(CH3)2
N(CH3)2
Scheme 2.
SH
SCH2C6H5
S
H
HC N N
HC N N
SCH2C6H5
N(CH3)2
N(CH3)2
a
b
[5–7]. The thione form is relatively unstable in the
monomeric form and tends to convert into a more
stable thiol form by enethiolization (Scheme 2).
stretching frequency of the free Schiff base appeared
as a sharp band at 805 cm–1 was shifted to a lower
frequency (750 cm–1) due to M–N bonding. This fact
provides further evidence for thiolate coordination.
The ν(C=N) stretching frequency of the free Schiff
base observed at 1589 cm–1 shifted towards the low-
frequency region (1560 cm–1), supporting M–N bond.
Thiolate coordination was also supported by the
disappearance of the ν(M–S) band of the free Schiff
base appears at 1084 cm–1. This band also disappeared
from the IR spectra of the metal complexes, giving
evidence for the coordination through the thiolate
anion. Evidence for the coordination of the Schiff base
through both the thiolate sulfur and β-nitrogen also
comes from the observation in the IR spectra of the
complexes of the ν(M–S) and ν(M–N) bands at 460
and 503 cm–1, respectively [15].
IR spectra. The important IR spectral bands of the
ligand SB and its metal complexes were listed in
Table 1. The absence of the ν(S–H) absorbance at
about 2565 cm–1 indicates that in the solid state the
base exists primarily in the thione form. The
disappearance of the ν(N–H) bands in the spectra of
the metal complexes suggests deprotonation and
subsequent coordination through the thiolate anion.
The Schiff base also showed a strong band at 1589 cm–1,
which was assigned to the ν(C=N) modes of the free
ligand. In the IR spectra of the metal complexes, this
stretching band was shifted to lower frequencies,
because the C=N bond order decreases due to M–N
bond formation. The ν(C=S) mode of the free ligand
observed at 1084 cm–1 disappears from the IR spectra
of the complexes, thus supported the above suggestion
of the thiolate bonding to metal ions. The ν(C–S)
Molar conductance, magnetic moments and
electronic spectra. The molar conductance and
magnetic moments of the synthesized Schiff base and
Table 1. Important IR spectral bands of the ligand and metal complexes
ν, cm–1
Compound
N–H
3125
–
C=S
1084
–
C=N
1589
1560
1557
C–S
805
750
750
M–S
–
M–N
–
SB
[Ni(II)(SB)2]
[Cu(II)(SB)2]
460
465
503
501
–
–
[Zn(II)(SB)2]
–
–
1565
750
445
475
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 6 2019

SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL ACTIVITY OF THE SCHIFF BASE
1199
SCH2C6H5
CH
N N
(H3C)2N
SCH2C6H5
C
C
S
S
N
N CH
Zn2+
M2+
HC
N
N
C S
SCH3
N N
HC
S
C
N(CH3)2
SCH3
N(CH3)2
N(CH3)2
Fig. 1. Square-planar structure of the complexes M(II)(SB)2
Fig. 2. Tetrahedral structure of the complex [Zn(II)(SB)2].
[M = Ni(II), Cu(II)].
its metal complexes are given in Table 2. As judged
from the conductance values, the complexes were all
nonelectrolytes in nature [16]. Magnetic susceptibility
measurements (Table 2) showed that the complex
[Ni(II)(SB)2] was diamagnetic. The UV-Vis spectrum
of the complex in DMSO were given evidence for a
singlet ground state characteristic of square-planar
Ni(II) complexes. The three bands observed in the
adopted in this investigation [21–23]. The metal
complexes yielded clear inhibition zones around the
discs with all the three test bacteria (Table 4). As seen
from the table, the complexes demonstrated moderate
to strong activities against both gram-positive and
gram-negative bacteria compared to the antibacterial
standard Kanamycin.
1
1
EXPERIMENTAL
spectrum were assigned to the A1g → A2g (280 nm),
1A1g →1B1g (320 nm), and A1g →1A2g transitions
1
All reagents were of chemical grade purity and
solvents were purified by standard procedures. The IR
spectra were recorded on a Shimadzu FTIR-8101
spectrophotometer in the range 4000–225 cm–1 for KBr
disks. The 1H NMR (400 MHz) and 13C NMR
(100 MHz) spectra were recorded on a JEOL JNM-
A400 spectrometer in CDCl3 with TMS as internal
standard. The UV-Vis spectra were recorded on a
Shimadzu UV-160 spectrophotometer in the range 200–
900 nm. Conductivity measurements were carried out
in 10–3 M DMSO solutions at room temperature using
a SCHOTT Geräte CG 857 digital conductivity meter.
Magnetic measurements were performed using a
Sherwood Scientific magnetic susceptibility balance.
The metal contents were determined gravimetrically
[24]. Microanalyses (C, H N) were executed by using a
MLW-CHN micro analyser.
(360 nm), which were previously observed in the
electronic absorption spectra of such square-planar
Ni(II) complexes [17, 18]. Complex [Cu(II)(SB)2] was
paramagnetic (magnetic moment, 1.98 B.M) which
corresponds to one unpaired electron. The UV-vis
spectrum of the complex showed d–d bands at 342 and
2
2
292 nm (Table 3), arising from the B1g→ A1g and
2
2B1g→ E1g transitions, respectively, and characteristic
of a square-planar stereochemistry [19, 20]. The strong
band at 221 nm is presumably associated with a charge-
transfer transition. The charge-transfer band of
complex [Zn(II)(SB)2] was observed at 295 nm which
indicated that the complex diamagnetic in nature.
Together the above observations allowed us to suggest
that the complexes [Ni(II)(SB)2] and [Cu(II)(SB)2]
have a square-planar structure with the two ligands
occupying four stereochemical sites, while the
complex [Zn(II)(SB)2] has a tetrahedral geometry
(Figs. 1 and 2).
Table 2. Molar conductances and magnetic moments of the
complexes
Molar conductance,
Antibacterial activity. The synthesized compounds
were tested for antibacterial activity against three
pathogenic bacteria, two gram-negative (E. coli and S.
sonnei) and one gram-positive (B. subtilis). Disc
diffusion method is a widely accepted procedure for in
vitro investigation of the susceptibility of micro-
organisms to the compounds, so this method was
Complex
SB
μeff, B.M.
Ω–1 cm2 mol–1
2.20
–
[Ni(II)(SB)2]
[Cu(II)(SB)2]
[Zn(II)(SB)2]
1.90
Dia
1.98
Dia
2.98
3.15
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 6 2019

1200
LATIF et al.
Table 3. UV-Vis spectral data for the complexes
λ
max, nm
Complex
band I
280
band II
320
292
–
band III
360
[Ni(II)(SB)2]
[Cu(II)(SB)2]
[Zn(II)(SB)2]
221
342
295
–
Table 4. Results of antibacterial activity testing
Diameter of the inhibition zone, mm
Compound
E. coli
13
S. sonnei
B. subtilis
SB
14
15
16
13
20
13
17
19
15
22
[Ni(SB)2]
[Cu(SB)2]
[Zn(SB)2]
Kanamycin
16
18
14
20
S-benzyldithiocarbazate (SBDTC) was prepared by
the procedure described in [15].
that formed was filtered off, washed with hot ethanol,
and dried in vacuo over anhydrous CaCl2.
Synthesis of benzyl N'-(4-dimethylaminobenzyl-
idene)hydrazinecarbodithioate (SB). A solution of
1.98 g (10 mmol) of SBDTC in 50‒60 mL of hot
absolute ethanol was added to a solution of the equi-
molar amount of 4-(dimethylamino)benzaldehyde in
20 mL of the same solvent. The mixture was refluxed
for 40 min. The yellow precipitate that formed was
separated and dried in vacuo over anhydrous CaCl2,
Yield 68%, orange powder, mp 178°C. 1H NMR
spectrum, δ, ppm: 3.02 s [6H, N(CH3)2], 4.56 m (2H,
SCH2), 6.64 d (J = 9.2 Hz, H12,14, C6H4), (J = 6.8 Hz,
H11,15, C6H4), 7.55–7.30 m (5H, C6H5), 7.75 s (1H,
CH=N), 10.22 s (1H, N–NH). 13C NMR spectrum, δC,
ppm: 38.39, 39.26, 40.06, 111.59, 120.07, 127.36,
127.89, 128.54, 128.71, 129.14, 129.42, 129.54, 135.69,
136.22, 146.80, 152.19, 164.0, 196.36. Calculated, %: C
61.97; H 5.81; S 19.46; N 12.75. C17H19S2N3. Found, %:
C 61.99; H 5.81; S 19.40; N 12.74.
[Ni(SB)2]. Yield 70%, color greenish brown, mp
255°C. Calculated, %: C 57.06; H 5.07; N 11.74; S
17.92; Ni 8.20. C34H36N6S4Ni Found, %: C 57.10; H
5.03; N 11.72; S 17.94; Ni 8.20.
[Cu(SB)2]. Yield 65%, color reddish, mp 195°C.
Calculated, %: C 56.68; H 5.03; N 11.66; S 17.80; Cu
8.82. C34H36N6S4Cu. Found, %: C 56.70; H 5.05; N
11.69; S 17.76; Cu 8.85.
[Ni(SB)2]. Yield 64%, color off white, mp 210°C.
Calculated, %: C 56.53; H 5.02; N 11.63; S 17.34; Zn
9.05. C34H36N6S4Zn. Found, %: C 56.57; H 5.05; N
11.59; S 17.38; Zn 9.10.
The standard test microorganisms for antibacterial
studies were collected from the department of pharmacy,
Rajshahi University, Rajshahi. The diameters of zones
of inihibition produced by the compounds were com-
pared with standard antibiotics (Kanamycin 30 µg/disc).
The experiment was performed in duplicate to minimize
errors.
Synthesis of metal complexes of the Schiff base
(general procedure): A solution of 0.329 g (1 mmol)
of SB in 70 mL of hot absolute ethanol was added to a
solution of the metal salt hydrate [Ni(NO3)2·6H2O]
(0.145 g, 0.5 mmol ), [Cu(NO3)2·3H2O] (0.121 g,
0.5 mmol), or [Zn(NO3)2·6H2O] (0.148 g, 0.5 mmol)
in 20 mL of absolute ethanol. The mixture was
refluxed for 40 min and then cooled. The precipitate
CONCLUSIONS
The Schiff base N'-(4-dimethylaminobenzylidene)
hydrazinecarbodithioate was prepared by the con-
densation of S-benzyldithiocarbazate and 4-(dimethyl-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 6 2019

SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL ACTIVITY OF THE SCHIFF BASE
1201
Chem., 1977, vol. 39(10), p. 1785. doi 10.1016/0022-
1902(77)80202-9
amino)benzaldehyde. The present study revealed that
the Schiff base acts as a uninegative bidentate ligand
with its NS donor set and forms neutral bischelated
Ni(II), Cu(II), and Zn(II) complexes. The Ni(II) and
Cu(II) complexes have a square-planar geometry,
while the Zn(II) complex is tetrahedral. The ligand and
its metal complexes showed significant antimicrobial
activity toward some bacterial strains.
8. Akbar Ali, M., Hossain, G., Mazumder, S.M.M.H.,
Nazimuddin, M., and Tarafder, M.T.H., Polyhedron,
1987, vol. 6(8), pp. 1653. doi 10.1016/S0277-5387(00)
80766-4
9. Hazari, S.K.S., Palit, D., Dey, B.K., and Mazumder, J.L.,
Chittagong Univ. Studies, Part 2, 1996, vol. 20, no. 1,
p. 53.
10. Akbar Ali, M., Chowdhury, D.A., and Nazimuddin, M.,
Polyhedron, 1984, vol. 3(5), p. 595. doi 10.1016/S0277-
5387(00)88093-6
11. How, F.N.F., Crouse, K., Tahir, M.I.M., Tarafder, M.T.H.,
and Cowley, A.R., Polyhedron, 2008, vol. 27(15),
p. 3325. doi 10.1016/j.poly.2008.07.022
12. Ravoof, T.B.S.A, Crouse, K., Tahir, M.I.M., Cowley, A.R.,
and Akbar Ali, M., Polyhedron, 2007, vol. 26(6),
p. 1159. doi 10.1016/j.poly.2006.03.007
13. Chan, M.H.E., Crouse, K., Tahir, M.I.M., Rosli, R.,
Umar-Tsafe, N., and Cowley, A.R., Polyhedron, 2008,
vol. 27(4), p. 1141. doi 10.1016/j.poly.2007.11.035
FUNDING
This work was partially supported by the Ministry
of Science and Technology, Bangladesh, through a
research & development fund. Biological activities
were evaluated at the Department of Pharmacy,
University of Rajshahi.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
14. Garoufis, A., Hadjikakou, S.K., and Hadjiliadis, N.,
Coord. Chem. Rev., 2009, vol. 253, nos. 9–10, p. 1384.
doi 10.1016/j.ccr.2008.09.011
1. Zangrando, E., Islam, M.T., Al-Amin, M., Islam, A.A.,
Sheikh, M.C., Tarafder, M.T.H., Miyatake, R., Zahan, R.,
and Hossain, M.A., Inorg. Chim. Acta, 2015, vol. 427,
p. 278. doi 10.1016/j.ica.2014.12.014
15. Akbar Ali, M. and Tarafdar, M.T.H., J. Inorg. Nucl.
Chem., 1977, vol. 39(10), p. 1785. doi 10.1016/0022-
1902(77)80202-9
16. Geary, W.J., Coord. Chem. Rev., 1971, vol. 7(1), p. 81.
2. Nunez-Montenegro, A., Carballo, R., and Vazquez-
Lopez, E.R., Polyhedron, 2008, vol. 27, p. 2867. doi
10.1016/j.poly.2008.06.018
doi 10.1016/S0010-8545(00)80009-0
17. Gray, H.B., and Ballhausen, C.J., J. Am. Chem. Soc.,
1963, vol. 85(3), p. 260. doi 10.1021/ja00886a002
3. Ali, M.A., Mirza, A.H., Nazimuddin, M., Rahman, H.,
and Butcher, R.J., Trans. Metal Chem., 2002, vol. 27(3),
p. 268. doi 10.1023/A:1014894403685
4. Tarafder, M.T.H., Ali, A.M., Wong, Y.W., Wong, S.I.,
and Crouse, K.A., Synth. React. Inorg. Met.-Org.
Chem., 2001, vol. 31, p. 115. doi 10.1081/SIM-
100001937
5. Kudrat-E-Zahan, Md., Islam, M.S., and Abul Bashar, Md.,
Russ. J. Gen. Chem., 2015, vol. 85, no. 3, p. 667. doi
10.1134/S1070363215030238
18. Jorgensen, C.K., J. Inorg. Nucl. Chem., 1962, vol. 24
(12), p. 1571. doi 10.1016/0022-1902(62)80011-6
19. Figgis, B.N., Interscience, New York, 1967, p. 316.
20. Malik,W.U., Teoiia, M.P., and Rastogi, D.K., J. Inorg.
Nucl. Chem., 1973, vol. 35(12), p. 4047. doi
10.1016/0022-1902(73)80392-6
21. Brown, D.F.J. and Kothari, D., J. Clin. Path., 1975,
vol. 28, p. 779.
22. Bauer, A.W., Arch. Int. Med., 1959, vol. 104(2), p. 208.
doi 10.1001/archinte.1959.00270080034004
23. Gunthkal, M.S.,Timmanagoud, R.G., and Sangamesh, A.P.,
6. Kudrat-E-Zahan, Md. and Islam, M.S., Russ. J. Gen.
Chem., 2015, vol. 85, no. 4, p. 979. doi 10.1134/
S1070363215040350
Oriental J. Chem., 2000, vol. 16(1), p. 151.
7. Akbar Ali, M. and Tarafder, M.T.H., J. Inorg. Nucl.
24. Vogel, A.I., Long Mans and ELBS, 1969.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 6 2019