Syntheses, characterization and antimicrobial screening of N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide and its Cu(I), Ni(II), Mn(II), Co(III) and Zn(II) complexes

Article abstract of DOI:10.14233/ajchem.2013.13393

N-(Benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide (DCBS2ABT) was synthesized by the condensation (by refluxing) of 2-aminobenzothiazole and 2,5-dichlorobenzenesulphonylchloride in acetone at 230 °C. The resulting crude precipitates were recrystallized

Full text of DOI:10.14233/ajchem.2013.13393

Asian Journal of Chemistry; Vol. 25, No. 4 (2013), 2199-2207
http://dx.doi.org/10.14233/ajchem.2013.13393
Syntheses, Characterization and Antimicrobial Screening of N-(Benzothiazol-2-yl)-2,5-
Dichlorobenzenesulphonamide and Its Cu(I), Ni(II), Mn(II), Co(III) and Zn(II) Complexes
1,*
1
1
2
L.N. OBASI , C.O.B. OKOYE , P.O. UKOHA and K.F. CHAH
1Department of Pure and Industrial Chemistry, University of Nigeria, Nsukka, Enugu State, Nigeria
2Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka, Nigeria
*Corresponding author: E-mail: nnamdi.obasi@unn.edu.ng; obasinl@yahoo.com
(Received: 5 January 2012;
Accepted: 17 October 2012)
AJC-12312
N-(Benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide (DCBS2ABT) was synthesized by the condensation (by refluxing) of 2-
aminobenzothiazole and 2,5-dichlorobenzenesulphonylchloride in acetone at 230 ºC. The resulting crude precipitates were recrystallized
in absolute ethanol. Five metal complexes of copper(I), nickel(II), manganese(II), cobalt(III) and zinc(II) of the ligand were synthesized.
The compounds were characterized using magnetic susceptibility measurements, UV/visible spectrophotometry, elemental microanalysis,
infrared, 1H and 13C NMR spectroscopies. The antimicrobial tests of the ligands and its metal complexes were carried out on both multi-
resistant bacterial strains isolated under clinical conditions and cultured species using agar-well diffusion method. The multi-resistant
bacterial strains used were Escherichia coli, Proteus species, Pseudomonas aeroginosa and Staphylococcus aureus were isolated from
dogs. The culture species were Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) Staphylococcus aureus (ATCC
25923) and the fungi, Candida krusei (ATCC 6258) and Candida albicans (ATCC 90028). The tests were performed both in vitro and in
vivo. Thus the inhibition zone diameter, the minimum inhibitory concentration and the lethal and effective concentrations (LC50 and EC50)
were determined. The antimicrobial activities of the compounds were compared with those of ciprofloxacin and trimethoprim-
sulphamethoxazole as antibacterial agents and fluconazole as an antifungal drug.All the compounds showed varying activities against the
cultured typed bacteria and fungi used. However, they were less active than the standard drugs used except fluconazole, which did not
show any activity against Candida krusei (ATCC 6258) but the ligand, DCBS2ABT and all the metal complexes synthesized were very
active against it. The lethal concentration (LC50) ranged from 81.00 6.8-256.30 36.7 ppm. These are within the permissible concentrations.
Key Words: N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide, Metal complexes, Antimicrobial.
the results obtained showed that the compounds were signifi-
cantly active against Staphylococcus aureaus and Escherichia
coli. Some novel N-(benzothiazol-2-yl)ethanamides were also
synthesized and characterized by Obasi, et al.8 and were
screened in vitro and in vivo for antibacterial activity. The
compounds were very stable and showed high antibacterial
activities against both gram-positive and gram-negative
bacteria tested9. The present work is aimed at synthesizing
new derivative of 2-aminobenzothiazole and its metal(II)
complexes, characterizing them and investigating how their
sstructural differences affects antimicrobial activities when
compared with conventional sulfonamides.
INTRODUCTION
The search for potent antiinfective agents occupies an
important position in science with the upsurge in disease
diversity and declining sensitivity of the implicated organisms
to available agents1,2. Interest in the coordination chemistry of
thiazole and its derivatives with metal ions has risen due to
the important role they play in biological systems3. Thiazole
are known to posses antitubercular4, hypotensive and hypother-
mic5 activities. Studies have shown that the metal complexes
of sulfa drugs promote rapid healing of skin disorder, for
instance, silver(I) sulfadiazine complex is used for human burnt
treatment and zinc(II) sulfadiazine in preventing bacterial
infections in burnt animals6.
EXPERIMENTAL
Mercury(II) and copper(II) complexes of 6-methyl-2-
aminobenzothiazole have equally been discovered to show
high activity against Aspergillus niger, Alternaria alternate,
Curvularia plunata and Penicillium fumculorus7. Obasi, et al.8
worked on some sulfonyl derivatives of 2-aminothiazole and
The ligand, N-(benzothiazol-2-yl)-2,5-dichloroben-
zenesulphonamide (DCBS2ABT) was prepared based on our
modified method from that by Sprague et al.10. All reagents
were of analytical grade and were used as supplied except
otherwise stated. UV-visible spectra of the ligand and its metal

2200 Obasi et al.
Asian J. Chem.
complexes were obtained on UV-2550 UV-VISIBLE Spectropho-
tometer, (SHIMADZU). FTIR spectra of the compounds were
run as Nujol mulls on FTIR-84005 FTIR Spectrophotometer,
chloride tetrahydrate (0.20 g; 1 mmol). This was refluxed for
0.5 h at 120 ºC during which a white amorphous solid was
formed. This was filtered and dried in a stream of air and stored
in desiccator (Scheme-III).
1
(SHIMADZU). 13C and H NMR spectra were recorded on
Bruker-BioSpin 500 MHz NMR spectrometer (UK) using
DMSO and CDCl3 as solvents respectively. The proton NMR
peaks were observed at 400 MHz whereas the carbon-13 spectra
were observed at about 200 MHz. Elemental analysis was done
using LECO-CHNS 932 microanalysis apparatus and the
magnetic susceptibility of the complexes were determined
using Sherwood scientific magnetic susceptibility balance,
Mk1 model (Cambridge, UK) both at department of Pure and
Applied Chemistry, University of Strathclyde, Scotland, UK.
Synthesis of N-(benzothiazol-2-yl)-2, 5-dichloroben-
zenesulphonamide (DCBS2ABT): To a solution of 2-
aminobenzothiazole (3.0 g; 20 mmol) in acetone (15 mL) was
added a solution of 2,5-dichlorobenzenesulphonylchloride (5.0
g; 20 mmol) in acetone (20 mL) with stirring. The mixture
was refluxed for 1 h at 230 ºC. A milkish white precipitate
was formed on refluxing and was recrystallized in absolute
ethanol (yield ca. 79 %) (Scheme-I).
S
NH
2
O
NiCl2.6H2O
Cl
N
S
+
O
120 °C
DMF
Cl
N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulfonamide
S
N
2+
NH
O
Cl
S
O
Cl
2Cl-
Ni
Cl
O
N
S
Cl
O
NH
S
Cl
Bis [N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide]nickel(II) chloride
Scheme-II: Synthesis of bis-[N-(benzothiazol-2-yl)-2, 5-dichlorobenzene-
sulphonamide]nickel(II) chloride (Ni(II)DCBS2ABT)
N
O
+
Cl
H N
2
S
S
NH
S
2
O
O
Cl
Cl
S
N
MnCl .4H O
+
2
2
O
2-aminobenzothiazole
2,5-dichlorobenzenesulfonyl chloride
120 °C
DMF
acetone
230 °C
Cl
N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulfonamide
S
NH
O
HCl
S
+
Cl
S
N
NH
O
O
Cl
S
N
O
Cl
S
Cl
Cl
Mn
Cl
Cl
N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulfonamide
Scheme-I:Synthesis of N-(benzothiazol-2-yl)-2, 5-dichlorobenzene-
sulphonamide (DCBS2ABT)
O
N
S
Cl
O
NH
Synthesis of bis-[N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide] nickel(II) chloride (Ni(II)DCBS-
2ABT): To a solution of N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide (0.72 g; 2.00 mmol) in DMF (10 mL)
was added aqueous solution of nickel(II) chloride hexahydrate
(0.28 g; 1.00 mmol). This was refluxed for 0.5 h at 120 ºC
during which a white amorphous solid was formed. This was
filtered and dried in a stream of air and stored in desiccator
(Scheme-II).
Bis [N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide]dichloromanganese(II)
Scheme-III: Synthesis of bis-[N-(benzothiazol-2-yl)-2,5- dichlorobenzene-
sulphonamide]dichloromanganese(II) (Mn(II)DCBS2ABT)
Synthesis of bis-[N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide] dichlorocobalt(III) ion (Co(III)DC-
BS2ABT): To a solution of N-(benzothiazol-2-yl)-2,5-
dichlorobenzenesulphonamide (0.72 g; 2 mmol) in DMF
(10 mL) was added aqueous solution of cobalt(II) chloride
hexahydrate (0.24 g; 1 mmol). This was refluxed for 0.5 h at
120 ºC during which a blue powdery solid was formed. This
was filtered and dried in a stream of air and stored in desiccator
(Scheme-IV).
Synthesis of bis-[N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide] dichloromanganese(II) (Mn(II)DC-
BS2ABT): To a solution of N-(benzothiazol-2-yl)-2,5-
dichlorobenzenesulphonamide (0.72 g; 2.00 mmol) in DMF
(10 mL) was added aqueous solution of manganese(II)

Vol. 25, No. 4 (2013)
Syntheses of N-(Benzothiazol-2-yl)-2,5-Dichlorobenzenesulphonamide and Its Metal Complexes 2201
S
Synthesis of bis-[N-(benzothiazol-2-yl)-2,5-
dichlorobenzenesulphonamide] copper(I) chloride
NH
2
O
+
CoCl .6H O
2
2
Cl
S
N
(Cu(I)DCBS2ABT): To a solution of N-(benzothiazol-2-yl)-
2,5-dichlorobenzenesulphonamide (0.72 g; 2.00 mmol) in
DMF (10 mL) was added aqueous solution of copper(II)
chloride dihydrate (0.25 g; 1.00 mmol). This was refluxed for
0.5 h at 120 ºC during which a light green amorphous solid
was formed. This was filtered and dried in a stream of air and
stored in desiccator (Scheme-VI).
O
120 °C
DMF
Cl
N-(benzothiazol-2-yl)-2,5-chlorobenzenesulfonamide
+
S
N
NH
S
O
Cl
NH
S
2
O
CuCl .2H O
+
2
2
O
Cl
S
N
O
120 °C
DMF
Cl
S
Cl
Co
Cl
Cl
Cl
N-(benzothiazol-2-yl)-2,5-chlorobenzenesulfonamide
+
O
N
S
N
Cl
O
NH
NH
O
Cl
S
S
O
Bis [N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide]dichlorocobalt(III) ion
Cl
Scheme-IV: Synthesis of bis-[N-(benzothiazol-2-yl)-2, 5-dichlorobenzen-
esulphonamide]dichlorocobalt(III) ion (Co(III)DCBS2ABT)
Cl-
Cu
Cl
Synthesis of bis-[N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide] zinc(II) chloride (Zn(II)DCBS2ABT):
To a solution of N-(benzothiazol-2-yl)-2,5-dichlorobenzene-
sulphonamide (0.72 g; 2.00 mmol) in DMF (10 mL) was added
aqueous solution of zinc(II) acetate dihydrate (0.29 g; 1.00
mmol). This was refluxed for 0.5 h at 120 ºC during, which a
white crystalline solid was formed. This was filtered and dried
in a stream of air and stored in desiccator (Scheme-V).
O
N
S
Cl
O
NH
S
Bis [N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide]copper(I) chloride
Scheme-VI: Synthesis of bis-[N-(benzothiazol-2-yl)-2, 5-dichlorobenzene-
sulphonamide]copper(I) chloride (Cu(I)DCBS2ABT)
Antimicrobial properties
In vitro tests: Multi-resistant bacterial strains isolated
under clinical conditions and typed strains (ATCC cultures)
were used in the study. The bacterial strains used were
Escherichia coli strains (E. Coli strain 1 and E. coli strain 15),
Proteus species strains (Proteus spp strains 25, Proteus spp
strains 26), Pseudomonas aeroginosa strains 34 and multi-
resistant Staphylococcus aureus (SR) strain. The bacteria
Typed strains (ATCC cultures) used were Pseudomonas
aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922),
Staphylococcus aureus (ATCC 25923). Fungi typed strains
(ATCC cultures) used were Candida krusei (ATCC 6258) and
Candida albicans (ATCC 90028). The typed strains were
obtained from bioresources development and conservation
program (BDCP), International Centre for Ethnomedicine and
Drug Development (IntaceEED), Nsukka, Nigeria.
S
NH
2
O
Zn(CH3COO)2
Cl
S
N
+
O
120 °C
DMF
Cl
N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulfonamide
2+
S
N
NH
O
Cl
S
O
2Cl-
Cl
The antibacterial and antifungal activities of the ligand,
DCBS2ABT and its metal complexes e.g., Ni(II)DCBS2ABT,
Mn(II)DCBS2ABT, Co(III)DCBS2ABT, Zn(II)DCBS2ABT,
Cu(I)DCBS2ABT against these multi-resistant bacteria were
determined using the agar well diffusion method as described
by Chah et al.11. Mueller-Hinton agar plates were inoculated
with 0.1 mL of 3 h broth culture of the test bacteria. Using a
cork borer, wells (7 mm in diameter and 2.5 mm deep) were
bored into the inoculated agar. The test compounds were
solubilized in 20 % v/v dimethyl sulfoxide and 0.05 mL of
Zn
Cl
O
S
N
S
Cl
O
NH
Bis [N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide]zinc(II) chloride
Scheme-V: Synthesis of bis-[N-(benzothiazol-2-yl)-2, 5-dichlorobenzene-
sulphonamide]zinc(II) chloride (Zn(II)DCBS2ABT)

2202 Obasi et al.
Asian J. Chem.
TABLE-1
PHYSICAL PROPERTIES OF THE LIGAND, DCS2ABT AND OF ITS METAL COMPLEXES, THE MAGNETIC
PROPERTIES OF THE COMPLEXES AND ELEMENTAL MICROANALYSIS OF THE LIGAND
S. No.
Samples
DCBS2ABT
m.p. (oC)
260-262
251-253
249-251
255-257
257-259
262-264
Colour
Milky
Texture
Powdery
Mw
µeff (BM)
-
No. of Electrons
Properties
-
1
2
3
4
5
6
359.00
776.69
843.94
847.93
783.39
817.05
-
Ni(II)DCBS2ABT
Mn(II)DCBS2ABT
Co(III)DCBS2ABT
Zn(II)DCBS2ABT
Cu(I)DCBS2ABT
White
Amorphous
Amorphous
Powdery
1.51
2.05
0.68
0.68
0.52
0
1
0
0
0
Diamagnetic
Paramagnetic
Diamagnetic
Diamagnetic
Diamagnetic
White
Blue
White
Crystalline
Amorphous
Light green
Elemental microanalysis of the ligand, DCBS2ABT
C (%) H (%)
N (%)
Calc.
43.45
Found
42.97
Calc.
2.23
Found
2.25
Calc.
7.80
Found
7.42
DCBS2ABT
TABLE-2
UV/VISIBLE SPECTRAL RESULT OF DCBS2ABT AND ITS COMPLEXES
Samples
Assignment
π→ π*; n→ π*
λmax (nm)
ν1 (cm-1)
ν2 (cm-1)
ν 3 (cm-1)
10-3 ∈1
1.63
10-4 ∈2
2.50
191
10-5 ∈3
DCBS2ABT
Ni(II)DCBS2ABT
216.4; 370.0
734.0; 310.0
ν1 = 1T2 (F) ← 1T1 (F)
ν1 =2T1g(H) ← 2A1g
ν2 =2Eg (H) ← 2Alg
ν1 =1T2g(I) ←1T1g(I)
ν2 = 1A2g(I) ← 1T1g(I)
ν3 = LMCT
13 620
32 260
32 260
34 660
32.9
Mn(II)DCBS2ABT 310.0; 288.5; 273.5
36 560
36 560
2083
211
21.1
17.7
Co(III)DCBS2ABT 490.5; 418.5; 311.0
32 260
34 660
34.7
4.03
Zn(II)DCBS2ABT
Cu(I)DCBS2ABT
310.5; 300.5; 281.5
317.5; 311.5
33 110
31 500
33 300
32 100
35 500
1180
1890
131
184
12.6
MLCT
MLCT
Legend: LMCT = Ligand-Metal Charge Transfer Transition; MLCT = Metal-Ligand Charge Transfer Transition
each compound at a concentration of 20 mg/mL were delivered
into the wells. One of the wells contained 20 % v/v DMSO
and served as control. The plates for antibacterial screening
were incubated at 37 ºC for 24 h while the fungi were incubated
at 30 ºC for 48 h and assessment of activity was based on the
measurement of the diameter of inhibition zone (IZD) around
the wells. The test was performed in triplicates, mean inhibitory
zone diameter was recorded to the nearest whole millimetre.
The minimum inhibitory concentrations (MICs) of the
test compounds were determined using the agar dilution
method as described by Ojo, et al.12. Two-fold serial dilutions
of test compounds were made in 20 % v/v DMSO. One
millilitre of each serial dilution was added to 19 mL of sterile
Mueller-Hinton agar maintained at 45 ºC, thoroughly mixed
and poured into a sterile plate and the medium allowed to
solidify. The final concentrations of the compounds ranged
from 20 mg/mL to 1.25 mg/mL. Amended media were incu-
bated overnight at 37 ºC to check for sterility. Overnight
nutrient broth cultures of the test bacteria were adjusted to
contain approximately 108 cfu/mL and 0.025 mL of each of
the test organisms was spot-inoculated on the amended
culture media. Inoculated plates were incubated at 37 ºC for
24 h and observed for presence of visible growth. The mini-
mum inhibition concentration was determined as the value of
the lowest concentration that completely suppressed growth
of the organisms.
shrimp nauplii in 1 mL of autoclaved sea water were put into
Bijou bottles using a Pasteur pipette under a stereo-microscope
with a light source. They were separated into 7 groups in
triplicate. Increasing concentrations (10, 100, 1000 ppm) of
the synthesized compounds were added into each of the
triplicate and distilled water was added into the control group.
The nauplii were incubated at room temperature (37 ºC) for
24 h after which the survivors in each well were counted. The
results were analyzed using Finney ProbitAnalysis (MS-DOS-
Computer-Program) to determine the LC50 at 95 % confidence
interval. Weak nauplii were noted as an indication of central
nervous system depression.
RESULTS AND DISCUSSION
The equations of reactions for the syntheses of the ligand,
DCBS2ABT and its metal complexes are represented in
Schemes I-VI.
Table-1 shows some physical properties of both ligand
and its metal complexes. The melting point of the ligand,
DCBS2ABT is 260-262 ºC while those of the complexes range
from 249-264 ºC. The ligand has a milky colour while the
nickel, manganese and zinc complexes are white. The cobalt
and the copper complexes are blue and light green respectively.
The ligand, DCBS2ABT and its cobalt complexes are powdery
while the nickel, manganese and copper complexes are amor-
phous. The zinc complex is however crystalline.
The result of the elemental microanalysis is recorded in
Table-1. The amount of carbon, hydrogen and nitrogen of the
ligand calculated theoretically correspond to a reasonable
extent with the experimental result.
In vivo tests [brine shrimps lethality test (BSLT)]: The
method of McLaughlin and coworkers was used to study the
bioactivity of the synthesized compounds13. Artemia salina
eggs obtained from a pet shop in Davis California was incu-
bated in natural sea water (from Bar Beach, Lagos, Nigeria)
in a dam-well under room condition. About ten (10) 48 h-
Electronic spectra: The electronic transition result of the
compounds synthesized are recorded in Table-2. Two bands

Vol. 25, No. 4 (2013)
Syntheses of N-(Benzothiazol-2-yl)-2,5-Dichlorobenzenesulphonamide and Its Metal Complexes 2203
TABLE-3
IR SPECTRA OF THE DCBS2ABT AND OF ITS COMPLEXES IN cm-1
DCBS2ABT Ni(II)DCBS2ABT Mn(II)DCBS2ABT Co(III)DCBS2ABT Zn(II)DCBS2ABT Cu(I)DCBS2ABT
Assignments
3442 (br,w)
2864(s)
2750(sh)
3421.83 (br)
2924.18 (s)
2853.78 (s)
1600.97 (s)
3415.08 (br)
2924.18 (s)
2853.78 (s)
1606.76 (s)
3350 (br)
2924.18 (s)
2853.78 (s)
1600.97 (s)
3420 (br)
2923.22 (s)
2853.78 (s)
1600.97 (s)
3400 (br)
2924.18 (s)
2853.78 (s)
N-H stretching vibration
C-H stretching vibration
1655.94(s)
1606.76 (s)
C=C stretching vibration of
aromatic ring
1544.20(s)
1461.95(s)
1546 (s)
1462.09 (s)
1375.29 (s)
1334.78 (s)
1253.77 (s)
954.80 (s)
836.17 (s)
651.96 (s)
587.34 (s)
350 (s)
1545.03 (s)
1462.09 (s)
1374.33 (s)
1335.75 (s)
1253.77 (s)
954.80 (s)
836.17 (s)
651.96 (s)
587.34 (s)
382.88 (s)
355 (s)
1546 (s)
1462.09(s)
1375.29 (s)
1334.78 (s)
1253.77 (s)
954.80 (s)
836.17 (s)
682.82 (s)
651.96 (s)
375 (s)
1549.86 (s)
1462.09 (s)
1376.26 (s)
1333.82 (s)
1253.77 (s)
954.80 (s)
835.21 (s)
682 (s)
1544.07 (s)
1462.09 (s)
C=N stretching vibration of
benzothiazole ring
1335.25(s)
1374.33 (s)
1334.78 (s)
SO2 stretching vibration
1285 (s)
808.98 (s)
745.6 3(s)
1253.77 (s)
954.80 (s)
835.21 (s)
682.82 (s)
651.96 (s)
374 (s)
C-Cl stretching vibration
C-H bending vibration in
substituted benzene ring
649.07 (s)
579.97 (s)
C-S-C stretching vibration
of thiazole ring
651.00 (s)
375 (s)
350 (s)
M-N, M-Cl and M-(C=C)
stretching vibrations
345 (s)
340 (s)
350 (s)
Legend: br= broad; m= medium; w= weak; s= strong; sh= shoulder
were observed for the ligand at 216.4 nm and 370.0 nm. They
are due to π→π* and n→π* transitions.
vibration of the ligand, DCBS2ABT, its Ni(II), Mn(II), Co(III),
Zn(II) and Cu(I) complexes respectively. Because of the
decrease in the stretching frequencies of the ligand up to 20
cm-1 when compared to the complexes, it is inferred that N-H
was involved in the coordination. Two strong peaks observed
between 2924-2750 cm-1 in all the compounds were assigned
to C-H stretching vibration. The strong peaks between 1656-
1601 cm-1 were assigned to C=C stretching vibration of
aromatic ring in all the compounds. Since there are marked
differences in the stretching frequencies of ligand compared
to the complexes up to 50 cm-1, we inferred that C=C was
involved in the coordination. Two strong peaks each between
1544-1462 cm-1 in all the compounds were assigned C=N
stretching vibration of benzothiazole ring. There was no signi-
ficant difference between the values in the ligand and the
complexes, so C=N was not involved in the coordination.
Strong peaks between 1376-1334 cm-1 in the compounds were
assigned to SO2 stretching vibration. This did not take part in
coordination since there is no significant difference in the
values observed for the ligand and the complexes. Strong peaks
at 1285 cm-1 for the ligand and 1254 cm-1 in all the complexes
were assigned to C-Cl stretching vibration. However, two
strong peaks each observed between 955-746 cm-1 in all the
compounds were assigned to C-H bending vibration of
substituted benzene ring. Also two strong peaks each observed
between 683-587 cm-1 in all the compounds were assigned to
C-S-C stretching vibration of thiazole ring. Strong peaks
observed in the complexes between 383-345 cm-1 were assigned
M-N, M- (C=C) and M-Cl stretching vibrations.
Nickel complex: For most octahedral and tetrahedral
Ni(II) complexes, three bands are expected, however for some
tetrahedral Ni(II) complexes like [NiI4]2- two broad bands may
be found14,15. Two bands were observed for Ni(II)DCBS2ABT
(13, 620 cm-1 and 32, 260 cm-1), they were assigned ν1 = 1T2
(F) ← 1T1(F) transition of square planar geometry.
Manganese complex: Three bands were observed for the
Mn(II) complex synthesized (32 260 cm-1, 34 660 cm-1 and 36
560 cm-1), the transitions are assigned as follows:
ν1 = 2T1g (H) ← 2A1g; ν2 = 2Eg (H) ← 2Alg transitions of octahe-
dral geometry.
Cobalt complex: In a cubic field, three spin-allowed
transitions are anticipated because of the splitting of the free-
ion ground 4F term and the accompanying 4P term. Of course
it is essentially a 2-electron transition from t2g5 eg2 to t2g3 eg4.
Three bands were observed for the cobalt complex (32, 260
cm-1, 34, 660 cm-1 and 36, 560 cm-1), it is assigned:
ν1 = 2T2g(H) ← 2T1g(H)
ν2 =2A2g(H) ← 2T1g(H)
ν3 = LMCT transitions
Zinc(II) complexes: Three bands were observed for the
Zn(II) complex synthesized, they are probably due to metal-
ligand charge transfer (MLCT) transition. We deduced a
tetrahedral geometry for the Zn(II) complex.
Copper(I) complexes: Two bands were observed for the
Cu(I) complex of the ligand synthesized (31, 500 cm-1 and 32,
100 cm-1). Based on the fact that the Cu(II) complex was
reduced to Cu(I) in this synthesis, there are no d←d transi-
tions16. With this fact, coupled with the colour of the complex,
it is presumed that the bands observed are as a result of charge
transfer transitions. We therefore proposed tetrahedral geometry
for the copper complex synthesized. The molar absorptivities
of the ligand and its complexes are also shown in Table-2.
IR Spectra of the DCBS2ABT and its metal complexes:
Table-3 gives the essential peaks of its metal and DCBS2ABT
complexes and presents a scheme for determining the mode
of ligation of the ligand. The broad peaks at 3442, 3422, 3415,
3350, 3420 and 3400 cm-1 were assigned to N-H stretching
1H and 13C NMR spectral data: 1H and 13C NMR spectra
data of DCBS2ABT and its metal complexes are shown on
Tables 4 and 5 respectively. The peaks at 13.49 ppm (1H, s)
for DCBS2ABT, 13.56 ppm (1H, s) for Ni(II)DCBS2ABT,
13.51 ppm (1H, s) for Co(III)DCBS2ABT and Cu(I)DCBS2ABT
are assigned to N-H protons. Peaks at 7.84 ppm (2H, d) and
7.69 ppm (IH, m) in DCBS2ABT, 7.38 ppm (1H, m) and 7.43
ppm (2 H, m) in Ni(II)DCBS2ABT, 7.30 ppm (1H, m) and
7.71 ppm (2H, d) in Co(III)DCBS2ABT, 7.61 ppm (3H, m) in
Zn(II)DCBS2ABT and 7.29 ppm (1H, m) and 7.71 ppm (2H,
d) in Cu(I)DCBS2ABT are assigned phenyl protons. Peaks at

2204 Obasi et al.
Asian J. Chem.
TABLE-4
1H NMR SPECTRA (ppm) OF THE DCBS2ABT AND OF ITS COMPLEXES
DCBS2ABT
Ni(II)DCBS2ABT Mn(II)DCBS2ABT Co(III)DCBS2ABT Zn(II)DCBS2ABT Cu(I)DCBS2ABT
Assignments
N-H protons
13.49 (1H, s)
7.69 (1H, m)
7.84 (2H, d)
13.56 (1H, s)
7.38 (1H, m)
7.43 (2H, d)
8.12 (4H, d)
-
-
13.51 (1H, s)
7.30 (1H, m)
7.71 (2H, d)
8.05 (4H, d)
-
13.51 (1H, s)
7.29 (1H, m)
7.71 (2H, d)
8.05 (4H, d)
7.61 (3H, m)
Phenyl protons
8.04 (4H, d)
-
8.26 (4H, d)
Benzothiazole
protons
TABLE-5
13C NMR SPECTRA (ppm) OF THE DCBS2ABT AND OF ITS COMPLEXES
7
S
2
6
NH
1
O
5
3
Cl
S
N
4
O
8
9
10
13
11
12
Cl
DCB
S2ABT
Ni(II)DCB
S2ABT
Mn(II)DCB
S2ABT
Co(III)DCB
S2ABT
Zn(II)DCB
S2ABT
Cu(I)DCB
S2ABT
Assignments
168.5
132.6
134.2
124.6
113.8
-
168.3
134.4
134.6
124.8
123.4
113.8
124.6
132.9
147.7
129.7
128.0
136.7
125.6
168.4
134.1
134.2
125.6
123.5
113.7
124.5
132.5
141.1
130.5
129.5
136.7
127.9
168.5
134.1
134.2
125.6
123.5
113.7
124.5
132.5
141.1
130.5
129.5
136.7
127.9
-
Benzothiazole carbon (C1)
Benzothiazole carbon (C2)
Benzothiazole carbon (C3)
Benzothiazole carbon (C4)
Benzothiazole carbon (C5)
Benzothiazole carbon (C6)
Benzothiazole carbon (C7)
Phenyl carbon (C8)
-
134.0
133.8
126.5
123.2
114.2
124.2
132.4
141.4
130.5
129.5
-
134.1
134.2
125.4
123.5
113.7
124.5
132.5
141.1
130.5
129.5
136.7
127.9
123.6
130.6
141.2
129.6
128.0
136.8
125.7
Phenyl carbon (C9)
Phenyl carbon (C10)
Phenyl carbon (C11)
Phenyl carbon (C12)
-
Phenyl carbon (C13)
8.04 ppm (4H, d) in DCBS2ABT, 8.12 ppm (4H, d) in
Ni(II)DCBS2ABT, 8.05 ppm (4H, d) in both Co(III)DCBS
2ABT and Cu(I)DCBS2ABT, 8.26 ppm (4H, d) in Zn(II)DCB
S2ABT are assigned to benzothiazole protons. However singlet
peaks within 2.54 ppm-3.38 ppm in Ni(II)DCBS2ABT, within
1.91 ppm-3.42 ppm in Zn(II)DCBS2ABT, 2.50 ppm and 3.35
ppm in both Co(III)DCBS2ABT and Cu(I)DCBS2 ABT are
due to the presence of the metal ion in the complexes. The
spectra observed in Mn(II)DCBS2ABT, Co(III)DCBS2ABT
and Cu(I)DCBS 2ABT showed almost the same splitting
pattern, an indication of nearly the same effect in the magnetic
field. Interestingly the peak indicating N-H proton completely
disappeared in the complex Zn(II)DCBS 2ABT with quite a
different splitting pattern from the other complexes in the same
series. More still, with the disorganization of the splitting
pattern in the phenyl moiety, it further confirms our prediction
that the phenyl moiety was involved in the complex formation.
The Mn(II) DCBS2ABT is paramagnetic and thus the spectral
result was not included.
Peaks at 168.3-168.5 ppm in the ligand and the complexes
except the copper and zinc complexes are assigned
benzothiazole ring carbon (C1), peaks at the 132.6 ppm in the
ligand and at the range of 134.0-134.4 in the complexes are
assigned benzothiazole ring carbons (C2). Peaks at 134.2 ppm
in the ligand, its manganese, cobalt and copper complexes
and peaks at 134.6 ppm and 133.8 ppm in the nickel and zinc
complexes respectively are assigned benzothiazole ring carbon
(C3). Peaks at the range of 124.6-126.5 ppm in the ligand and
in the metal complexes are assigned benzothiazole ring carbon
(C4). Peaks at 113.8 ppm in the ligand and the range of 123.2-
123.5 ppm in the metal complexes are assigned benzothiazole
ring carbon (C5). Peaks at the range of 113.7-114.2 ppm in
the metal complexes are assigned benzothiazole ring carbon
(C6). Peaks at 123.6 ppm in the ligand and at the range of
124.2-124.6 ppm in the metal complexes are assigned
benzothiazole ring carbon (C7). Peaks at 130.6 ppm in the
ligand and at the range of 132.4-132.9 ppm in the metal
complexes are assigned phenyl ring carbon (C8). Peaks in the
range of 141.2-147.7 ppm in the ligand and its metal complexes
are assigned phenyl ring carbon (C9). Peaks in the range of
129.6-130.5 ppm in the ligand and its metal complexes are
assigned phenyl ring carbon (C10). Peaks at 128.0 ppm and
129.5 ppm in both the ligand and its metal complexes are
Generally the difference in shifts, splitting patterns,
disappearance and disorganization of some peaks found in
the ligand with respect to the complexes and the presence of
the some peaks in the complexes that are not found in the
ligand are indication of complex formation.

Vol. 25, No. 4 (2013)
Syntheses of N-(Benzothiazol-2-yl)-2,5-Dichlorobenzenesulphonamide and Its Metal Complexes 2205
TABLE-6a
ANTIMICROBIAL ACTIVITY OF THE LIGAND AND OF ITS METAL COMPLEXES AGAINST
MULTI-RESISTANT BACTERIAL STRAINS ISOLATED UNDER CLINICAL CONDITIONS
Multi-resistant bacterial strains isolated from clinical conditions
Escherichia coli strains
Proteus species strains
Multi-resistant
Staphylococcus
aureus (SR) strain
Pseudomonas
aeroginosa strains 34
S.
Proteus spp
Strains 26
Proteus spp
strains 25
Samples
no.
E. coli Strain 1 E. coli Strain 15
IZD
(mm)
00
MIC
(mg/mL)
IZD
(mm)
00
MIC
(mg/mL)
IZD
(mm)
00
MIC
IZD
MIC
IZD
(mg/mL) (mm) (mg/mL) (mm)
MIC
(mg/mL)
IZD
(mm)
00
MIC
(mg/mL)
1
2
3
4
5
6
7
8
DCBS2ABT
00
00
00
00
00
00
00
00
11
12
00
9
00
00
00
00
00
00
00
10
27
00
00
00
00
Ni(II)DCBS2ABT
Mn(II)DCBS2ABT
00
00
00
00
00
00
00
00
00
00
10
00
00
00
Co(III)DCBS2ABT 00
00
00
00
00
00
10
00
00
00
Zn(II)DCBS2ABT
Cu(I)DCBS2ABT
Ciprofloxacin
00
9
00
00
00
00
00
00
00
00
00
10
00
00
10
10
10
10
00
00
00
0.05
0.025
00
0.05
0.025
00
0.05
0.025
25
0.05
0.025
0.05
0.025
00
0.05
0.025
Trimethoprim-
sulphamethoxazole
TABLE-6b
ANTIMICROBIAL ACTIVITY OF THE COMPOUNDS AGAINST TYPED STRAINS (ATCC CULTURES) MICROORGANISMS
Typed strains (ATCC Cultures)
Pseudomonas aeruginosa Escherichia coli
(ATCC 27853) (ATCC 25922)
IZD MIC
(mm) (mg/mL) (mm)
Staphylococcus aureus
Candida krusei
(ATCC 6258)
Candida albicans
(ATCC 90028)
S.
no.
Samples
(ATCC 25923)
IZD
(mm)
10
MIC
(mg/mL)
IZD
MIC
(mg/mL)
IZD MIC
(mm) (mg/mL)
IZD
(mm)
MIC
(mg/mL)
1
2
3
4
5
6
7
8
DCBS2ABT
10
00
00
00
00
00
00
13
18
00
00
11
00
00
00
00
10
17
10
00
12
12
12
12
12
14
-
10
10
10
10
10
10
-
10
11
11
11
11
10
-
10
10
10
10
10
10
-
Ni(II)DCBS2ABT
Mn(II)DCBS2ABT
Co(III)DCBS2ABT
Zn(II)DCBS2ABT
Cu(I)DCBS2ABT
Ciprofloxacin
00
00
00
00
00
00
00
00
00
00
00
00
00
12
10
10
10
25
0.005
0.025
0.005
0.025
0.005
0.025
Trimethoprim-
sulphamethoxazole
Fluconazole disk
-
-
-
-
9
-
-
-
-
-
-
00
00
20
10
assigned phenyl ring carbon (C11). More still, peaks at the
range of 136.7-136.8 ppm are assigned phenyl carbon (C12)
in the ligand, DCBS2ABT and its metal complexes. Peaks at
the range of 125.6-127.9 ppm in the ligand and its metal
complexes are assigned phenyl ring carbon (C13).
of octahedral geometry. The manganese complex investigated
showed effective magnetic moment of 2.05 BM. This is
indication of low spin paramagnetism corresponding to an
unpaired electron. We proposed d2sp3 hybridization of octa-
hedral geometry. The Cu(I) complex investigated showed
diamagnetism, indicating no unpaired electrons in the metal
d-orbitals. Since there is no possibility of electron pairing in
the d-orbitals, we are presuming that the ligand may have
induced reduction of the Cu2+ to Cu+. This is also confirmed
by the light green colour of the complex formed. We also
proposed sp3 hybridization of tetrahedral geometry for the
Cu(I) complex investigated.
Magnetic properties of the metal complexes: The result
of the magnetic properties of the present metal complexes is
shown in Table-1. The result gave an interesting data. It was
generally observed that the metal complexes were of low spin.
This is an indication that the ligand is a strong field and thus
was able to cause pairing of the electrons. As expected the
zinc complex investigated gave very small effective magnetic
moment, µeff (0.68 BM). Therefore the zinc complex is diamag-
netic and has sp3 hybridized geometry, thus tetrahedral
structure. Ni(II)DCBS2ABT complex showed effective
magnetic moment of 1.51 BM. This showed low spin confi-
guration and correspond to no unpaired electrons, indicating
diamagnetism. It is obvious that DCBS2ABT showed a strong
field orientation and has caused the paring of the electrons.
We therefore propose dsp2 hybridization with square planar
geometry. Co(III)DCBS2ABT showed effective magnetic
moment of 0.68 BM. This is an indication of low spin dia-
magnetism corresponding to no unpaired electron. Thus we
inferred that the ligand, DCBS2ABT may have induced
oxidation in the metal ion. We proposed sp3d2 hybridization
Antimicrobial activity of the ligand and of its metal
complexes: The antimicrobial activities of the ligand and of
its metal complexes are recorded in Tables 6a and 6b.
Table-6a showed the activities against multi-resistant
bacterial strains isolated under clinical conditions. The inhi-
bitory zone diameter (IZD) in mm and minimum inhibitory
concentration (MIC) in mg/mL of the compounds were deter-
mined. Two strains each of E. coli (E. coli strain 1 and E. coli
strain 15) and Proteus species (Proteus spp strains 25 and
Proteus spp strains 26), Pseudomonas aeroginosa strains 34
and multi-resistant Staphylococcus aureus (SR) strain, all iso-
lated from dogs at clinical conditions were used. Ciprofloxacin
and trimethoprim-sulphamethoxazole were used as the standard

2206 Obasi et al.
Asian J. Chem.
drugs. We determined the minimum inhibitory concentration
on the concentration range 0.125-10 mg/mL. We discarded
concentrations above 10 mg/mL. Based on this, only the ligand
showed activity against the tested microbes- E. coli Strain 15
and Pseudomonas aeroginosa strains 34 with minimum
inhibitory concentration of 10 mg/mL and inhibitory zone
diameter of 10 mm. The complexes showed no detectable
activity against the multi-resistant bacteria tested.
Lethal concentration (LC50) and effective concentration
(EC50): The result of the cytotoxic tests viz; Lethal concen-
tration (LC50) and effective concentration (EC50) is recorded
in Table-7.
TABLE-7
LETHAL CONCENTRATION (LC50) AND EFFECTIVE
CONCENTRATION (EC50) RESULTS IN ppm (CYTOTOXIC TEST)
S. No.
SAMPLES
LC50 (ppm)
158.80 26.7
81.00 6.8
EC50 (ppm)
15.9
Table-6b showed activities of the compounds against
Typed Strains (ATCC Cultures) microorganisms. The bacteria
cultures used are Pseudomonas aeruginosa (ATCC 27853),
Escherica coli (ATCC 25922) and Staphylococcus aureus
(ATCC 25923). The fungi, Candida krusei (ATCC 6258) and
Candida albicans (ATCC 90028) were also used. As with the
multi-resistant bacteria strains, the inhibitory zone diameter
in mm and minimum inhibitory concentration in mg/mL of
the compounds were determined. Ciprofloxacin and
trimethoprim-sulphamethoxazole were used as the antibac-
terial standard drugs while Fluconazole disk was used as
antifungal standard drugs.
1
2
3
4
5
6
DCBS2ABT
Ni(II)DCBS2ABT
Mn(II)DCBS2ABT
Co(III)DCBS2ABT
Zn(II)DCBS2ABT
Cu(I)DCBS2ABT
8.1
128.00 18.1
228.80 17.0
112.60 26.8
256.30 36.7
12.8
22.9
11.3
25.6
The result showed that all the synthesized compounds
showed high levels of bioactivity against 48 h-nauplii.
Ni(II)DCBS2ABT showed the highest bioactivity (81.00 6.8
ppm) with EC50 of 8.1 ppm while Cu(I)DCBS2ABT showed
the lowest bioactivity (256.30 36.7 ppm) with EC50 of 25.6
ppm. Comparing the compounds, the level of bioactivity is in
the order Ni(II)DCBS2ABT > Zn(II)DCBS2ABT >
Mn(II)DCBS2ABT > DCBS2ABT > Co(III)DCBS2ABT >
Cu(I)DCBS2ABT.
The minimum inhibitory concentration were determined
majorly on the concentration range of 0.125-10 mg/mL. Based
on this, all the compound synthesized showed activity against
at least one of the tested microbes. We adjudged that as in the
case of the activity against the multi-resistant bacteria,
Cu(I)DCBS2ABT showed the highest activity in that it was
active against all of the typed strains used-both the bacteria
except Escherichia coli strain 15 and multi-resistant Staphy-
lococcus aureus (SR) strain and all typed strains (ATCC
Cultures) microorganisms. The ligand, DCBS2ABT and its
zinc and nickel complexes did not show any activity against
the typed strains bacteria tested. The manganese and cobalt
complexes only showed activity against Proteus spp strains
26. The ligand, DCBS2ABT and all the complexes showed
activity against the fungi strains, Candida krusei (ATCC 6258)
and Candida albicans (ATCC 90028) tested with the copper
complex showing the highest activity with minimum inhibitory
concentration of 10 mg/mL and inhibitory zone diameters of
10 and 14 mm respectively. The nickel, manganese and cobalt
complexes did not show any detectable activity against the
bacteria typed strains (ATCC Cultures) used. The ligand was
not active against Escherichia coli (ATCC 25922) used.
As with the case of the fungus, Candida krusei (ATCC
6258), the ligand and its complexes synthesized were active
against Candida albicans (ATCC 90028) with the result
showing that the copper complex has more active antifungal
properties than the synthesized compounds. Fluconazole is
primarily fungistatic but can be fungicidal against certain
organisms in dose-dependent manner. Fluconazole was only
active against the typed strain Candida albicans (ATCC 90028)
but not against C. Krusei tested strains. This was confirmed
from literature17. We can conclude that the compounds showed
some degree of activity against the tested microorganisms
which to a large extent can be compared with the standard
drugs used. Since the standard antifungal drug used did not
show activity against the Candida krusei (ATCC 6258), we
can say that the ligand and its complexes were more active
that the fluconazole.
Brine shrimps lethality test is a rapid, inexpensive and
single bioassay for testing bioactivity of natural and synthetic
products, which in most cases correlates reasonably well with
cytotoxicity and antitumor properties of the products. The
results of Brine shrimps lethality test established that the ligand
and the complexes are very potent bioactive compounds. EC50
value for general bioactivity is approximately one tenth of the
value is the LC50 in Brine shrimps lethality test. The surviving
nauphii were dull and inactive, which may be a sign of central
nervous system depression.
Conclusion
N-(benzothiazol-2-yl)-2,5-dichlorobenzenesulphonamide
and its metal complexes were synthesized. The compounds
were characterized using magnetic susceptibility, UV/VIS
spectrophotometer, elemental microanalysis, infrared, proton
and 13C NMR. The spectral analyses confirmed the structures
of the compounds synthesized. The antimicrobial tests of the
ligand and its metal complexes were carried out on both multi-
resistant bacterial and fungal strains isolated under clinical
conditions and cultured species using agar-well diffusion
method. The tests were both in vitro and in vivo. The antimi-
crobial activities of the compounds were compared with those
of ciprofloxacin and trimethoprim-sulphamethoxazole as
antibacterial agents and Fluconazole as an antifungal drug. The
copper complex of N-(benzothiazol-2-yl)-2,5-dichloro-
benzenesulphonamide showed the highest activity in that it
was active against all of the typed strains used-both the bacteria
except Escherichia coli strain 15 and multi-resistant Staphy-
lococcus aureus strain and all Typed strains (ATCC Cultures)
microorganisms. The ligand, DCBS2ABT and its zinc and
nickel complexes did not show any activity against the typed
strains bacteria tested. All the other compounds synthesized
showed varying activities against the cultured typed bacteria

Vol. 25, No. 4 (2013)
Syntheses of N-(Benzothiazol-2-yl)-2,5-Dichlorobenzenesulphonamide and Its Metal Complexes 2207
4. M. Tsuruoka and I. Seikutsugaka, Med. Biol., 10, 296 (1947).
and fungi used. However, they were less active than the standard
bacterial drugs used and since the standard antifungal drug
(fluconazole) used did not show activity against the Candida
krusei (ATCC 6258), we can conclude that all the compounds
synthesized were more active than the fluconazole and can be
recommended for preclinical screening. The lethal concentrations
(LC50) were within the permissible concentrations.
5. R.P. Kapoor, M.K. Rastogi, R. Khanna and C.P. Garg, Indian J. Chem.,
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ACKNOWLEDGEMENTS
10. M.J. Sprague and L.W. Kissinger, J. Am. Chem. Soc., 63, 578 (1941).
11. K.F. Chah, C.A. Eze, C.E. Emuelosi and C.O. Esimone, J. Ethnopharm.,
104, 164 (2006).
Oneoftheauthors, Dr. L.N. ObasiisgratefultoDr. J. Reglinski,
Department of Pure and Applied Chemistry, University of
Strathclyde, Scotland, UK for useful discussions, and allow-
ing to use some equipments in the course of this work. The
authors are also grateful to Prof. Alexander Gray and his team
at SIPBS, also at the University of Strathclyde, Scotland, UK
for hosting him and to the University of Nigeria and the ETF
for sponsorship to the UK for a research visit.
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(2007).
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