Microwave assisted synthesis, characterization and biocidal activities of some new chelates of carbazole derived Schiff bases of cadmium and tin metals

Article abstract of DOI:10.1016/j.saa.2014.04.185

This study is planned to report the advancement of green microwave approach in the fabrication of a new series of biologically potent (N^X, where X = O/S) donor Schiff bases and their cadmium(II) and tin(II) complexes. The ligands and their metal complexes have been characterized in terms of elemental analysis, molar ionic conductance, magnetic moment and spectral (IR, UV-Vis, NMR ( ¹H, ¹¹⁹Sn), FAB-mass, thermal and XRD) data. The data revealed that the ligands coordinated to the metal center via nitrogen and oxygen/sulfur atoms and form an octahedral arrangement of the ligands around central metal atom. All compounds were evaluated for their in vitro antimicrobial activities against two pathogenic bacteria Bacillus subtilis and Escherichia coli and two fungi Aspergillus niger and Aspergillus flavus by standard disc diffusion method. The discs were stored in an incubator at 37 °C. The compounds were dissolved in DMF at 500 and 1000 ppm concentrations for screening biocidal activity. The compounds were dissolved in DMF to get the 100 and 200 ppm concentration of test solutions for screening fungicidal activity. The inhibition zone around each disc was measured (in mm) after 24 h and 96 h for biocidal and fungicidal activities respectively.

Full text of DOI:10.1016/j.saa.2014.04.185

Accepted Manuscript
Microwave assisted synthesis, characterization and biocidal activities of some
new chelates of carbazole derived Schiff-bases of cadmium and tin metals
Manju, Neelima, Nutan Sharma, Sulekh Chandra, Dinesh Kumar
PII:
S1386-1425(14)00769-0
http://dx.doi.org/10.1016/j.saa.2014.04.185
SAA 12160
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
6 February 2014
24 April 2014
30 April 2014
Please cite this article as: Manju, Neelima, N. Sharma, S. Chandra, D. Kumar, Microwave assisted synthesis,
characterization and biocidal activities of some new chelates of carbazole derived Schiff-bases of cadmium and tin
metals, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/
10.1016/j.saa.2014.04.185
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Microwave assisted synthesis, characterization and biocidal activities of some new chelates
of carbazole derived Schiff-bases of cadmium and tin metals
Manju1, Neelima1, Nutan Sharma1, Sulekh Chandra2 and Dinesh Kumar1*
1Department of Chemistry, Banasthali University, Banasthali, Rajasthan- 304022, India.
2Department of Chemistry, Zakir Husain College (University of Delhi), J.L. Nehru Marg, New
Delhi 110002, India.
HIGHLIGHTS
• A viable and ecological approach in synthesis.
• All the analyses results reveal the actuality of monomeric chelates of bidentate Schiff bases.
• The Cd(II) and Sn(II) complexes are diamagnetic at room temperature.
• Thermal data suggested that the complexes are more stable than the ligand.
• Antimicrobial activity statistics indicates that the complexes are more reactive than Schiff
bases.
GRAPHICAL ABSTRACT
• It has been observed on comparison with standard references compounds to antibiotic and
fungicides, the complexes are show good microbial activity than that of ligands.
A. Niger, Zone of inhibition (in mm), 96 h (Conc. in ppm) 100
A. Niger, Zone of inhibition (in mm), 96 h (Conc. in ppm) 200
A. Flavus, Zone of inhibition (in mm), 96 h (Conc. in ppm) 100
A. Flavus, Zone of inhibition (in mm), 96 h (Conc. in ppm) 200
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ABSTRACT
This study is planned to report the advancement of green microwave approach in the fabrication
of a new series of biologically potent (N^X, where X = O/S) donor Schiff bases and their
cadmium(II) and tin(II) complexes. The ligands and their metal complexes have been
characterized in terms of elemental analysis, molar ionic conductance, magnetic moment and
spectral (IR, UV-Vis, NMR (1H, 119Sn), FAB-mass, thermal and XRD) data. The data revealed
that the ligands coordinated to the metal center via nitrogen and oxygen/sulfur atoms and form
an octahedral arrangement of the ligands around central metal atom. All compounds were
evaluated for their in vitro antimicrobial activities against two pathogenic bacteria Bacillus
subtilis and Escherichia coli and two fungi Aspergillus niger and Aspergillus flavus by standard
disc diffusion method. The discs were stored in an incubator at 37 ℃. The compounds were
dissolved in DMF at 500 and 1000 ppm concentrations for screened biocidal activity. The
compounds were dissolved in DMF to get the 100 and 200 ppm concentration of test solutions
for screened fungicidal activity. The inhibition zone around each disc was measured (in mm)
after 24 h and 96 h for biocidal and fungicidal activities respectively.
Keywords: Schiff bases, spectral characterization, carbazole, antimicrobial activities, Cd(II) and
Sn(II) complexes.
Introduction
Modern chemists still prepare Schiff bases, and nowadays active and well-designed Schiff base
ligands are considered ‘‘privileged ligands’’. A great deal of Schiff bases have been reported to
possess antibacterial, antifungal and antitumor activities [1-6]. The effect of presence of various
substituents in the phenyl rings of aromatic Schiff bases on their antibacterial activity has been
reported [7]. Due to their multiple implications, the transition metal complexes with Schiff bases,
as ligands, are of paramount scientific attention. It has been found that in general the
complexation of Schiff bases with most transition metal atoms influences their antibacterial
activities [8-11]. A large number of heterocyclic systems which include mainly five and six
membered compounds represent a diverse group of molecular scaffolds. Several such
heterocyclic scaffolds have been successfully incorporated into novel drug leads and therapeutic
agents [12-14]. Schiff-base ligands with heterocyclic molecule and/or containing heteroatoms

such as N, O, and S show a broad biological activity and are of special interest because of the
variety of ways in which they are interacted to transition metal ions [15, 16]. All such brilliant
properties are depending on the number, nature and relative position of the donor atoms of a
Schiff base; the ligand allows a good control over the stereochemistry of the metallic centers in
homo and hetero polynuclear complexes [17-19]. Coordination behavior of metals have been
played central role in the extreme fast development of inorganic chemistry and the presence of
metal ions bonded to biologically active compounds may enhance their activity [20, 21]. To
prepare scaffolds of such compounds microwave irradiated reactions under solvent free or less
solvent conditions are attractive offering reduced pollution, low cost and offer high yields
together with simplicity in processing and handling [22-26]. In order to improve the biological
activity of the metal complexes, special attention has to be paid to the synthesis of different
topological complexes. In order to this, we have planned to prepare a list of semicarbazide
compounds containing the amide moiety have a strong ability to form metal complexes [27-29].
Semi and thiosemicarbazide and their metal complexes have an extensive concern because of
their biological activities, such as antitumour [30], antiviral [31], anticancer [32], antifungal [33],
antibacterial [34] and antimalarial [35]. Organotin compounds show the most varied range of
applications ranging from all sorts of biological activity to industrial catalysts for value-creating
technical processes. Furthermore, organotin(IV) complexes of Schiff bases present a wide
variety of interesting structural possibilities. Both aliphatic and aromatic Schiff bases in their
neutral and deprotonated forms have been used to yield adducts and chelates with variable
stoichiometry and different mode of coordination [36-40]. In addition, Cd(II) complex of Schiff
base 8-(1-(4-aminophenylamino)ethylidene)-2H-chromene-2,7(8H)-dione has been exhibited
photoluminescence originating from intraligand (π–π∗) transitions [41-44]. Diorganotin(IV)
complexes of N(4)-phenylthiosemicarbazones show biological activities, of these complexes
carried out in vitro against selected bacteria and K562 leukemia cells, respectively, have shown
that different substituted groups attached at the thiosemicarbazone moieties and different
diorganotin(IV) groups showed distinctive differences in the biological property [45-49]. Taking
into consideration the above proofs, Sn(II) and Cd (II) complexes of Schiff base derived from
condensation of thiosemicarbzide and semicarbazide were synthesized. The synthesized
compounds were characterized using various spectral techniques and evaluated for their

biological studies by disc diffusion technique. All the complexes were found to be more active as
compared to parent ligand.
Experimental
Materials
All commercial reagents were procured chemically pure and were of analytical reagent grade.
The solvents were dried and distilled before use the standard procedures cadmium and tin salts
were purchased from Sigma Aldrich and used without further purification. The bacterial strains
were procured from the Microbial Type Culture Collection (Institute of Microbial Technology,
Chandigarh, India). Bacterial strains Escherichia coli HB101 (MTCC-82), and Bacillus subtilis
(MTCC-441) and cultured on nutrient agar broth (Hi Media) and have been stored at 4 ℃.
Physical Methods
Chlorine was estimated gravimetrically as AgCl [50]. Carbon, hydrogen, nitrogen, and sulfur
(CHNS) were estimated by elemental analyzer (Perkin Elmer 2400 Series-II). Cadmium metal
was determined by titrimetrically and tin by gravimetrically. Molar ionic conductance of the
complexes were determined in DMF using a solution of about 10-3 M concentration on ESICO
model-1601 microprocessor based conductivity meter with a dip type cell with platinized
electrode [51, 52]. The magnetic susceptibilities measurements on powder form of the complexes
with magnetic susceptibility balance (Mk1) of Sherwood Scientific Corporation, UK using
MgSO4 as a celebrant at room temperature. Melting points were recorded on microtech
instrument of advanced melting point apparatus and are uncorrected. IR spectra in KBr pellets
were recorded using a Shimadzu FT-IR 8400 S spectrophotometer. Electronic spectra were
recorded in DMF with a lab India double beam UV-Visible spectrophotometer 3200.
Multinuclear magnetic resonance spectra (1H, and 119Sn) were recorded on a Bruker-400ACF
spectrophotometer in dimethylsulfoxide (DMSO-d6) using tetramethylsilane (TMS) as an
internal standard. FAB mass spectra were obtained from Department of Chemistry, University of
Delhi, New Delhi. Thermal studies were done by using Perkin Elmer TGA-4000. X-ray powder
diffraction spectra of the compound were obtained on the Bruker diffractometer using Cu (Kα)
target with Ni filter at room temperature. The wavelength used was 1.540600 Å and the

reflections from 20–80° were recorded. Microwave assisted procedure was carried out in
microwave synthesizer CHEM- Discover- 925105 of Lab India.
Synthesis of heteroaryl ketones [53-55]
Brown solids [TPC] (70%) 4’ and [BTPC] (76%) 4 i.e. heteroaryl ketones were separated out
as shown in Scheme 1. The separated brown solid was purified by passing through a column of
silica gel using 50% benzene in pet ether as eluent.
H
N
CH2C6H5
N
O2N
H2N
Fe/CH3COOH
O
O
H
N
HCOOEt/
EtONa
HCOOEt/
EtONa
N
NaNO2 /HCl
0-5 0C
CH2C6H5
H
N
HO
HO
N
1
O
O
2
ClN2
2'
ACONa/MeOH
H2O
ACONa/MeOH
H2O
CH2C6H5
Japp-klingemann reaction
Japp-klingemann reaction
H
N
H
N
N
N
NH
3
N
NH
3'
N
O
O
ACOH:HCl (4:1)
[Kent's Reagent]
ACOH:HCl (4:1)
[Kent's Reagent]
Fischer-indole
cyclization
Fischer-indole
cyclization
CH2C6H5
H
N
H
N
N
N
N
H
N
H
4'
O
O
4
[BTPC]
[TPC]
Scheme 1. Synthesis of heteroaryl ketones.
Micro wave- assisted synthesis of DPCS and BDPCS
The semicarbazones of 5,7,8,9-Tetrahydropyrazolo[4,3-b]carbazol-6-[1H]-one [TPC] and 9-
Benzyl-5,7,8,9-tetrahydropyrazolo[4,3-b]carbazol-6-[1H]-one [BTPC] were prepared by the
condensation with semicarbazide hydrochloride in (1:1) ratio in dry absolute ethanol as shown in

Scheme 2. The contents were refluxed for about 5−6 min under microwave radiations. Subjected
product was purified by recrystallization in the same solvent and dried. The analytical data came
in good consistence with the proposed formulae which are presented in Table 1.
O
H
N
H
N
NH2-NH-C-NH2
N
N
N
N
H
NH
O
HN
C O
H2N
(Z)-2-(8,9-dihydropyrazolo[4,3-b]carbazol-
6(1H,5H,7H)-ylidene)semicarbazone
5,7,8,9-tetrahydropyrazolo[4,3-b]
carbazol-6(1H)-one
DPCS
O
H
N
H
NH2-NH-C-NH2
N
N
N
N
N
H
O
N
H
HN
hydrazinecarboxamide
C O
H2N
(Z)-2-(9-benzyl-8,9-dihydropyrazolo[4,3-b]
carbazol-6(1H,5H,7H)-ylidene)semicarbazone
9-benzyl-5,7,8,9-tetrahydropyrazolo[4,3-b]
carbazol-6(1H)-one
BDPCS
Scheme 2. Structure of semicarbazones based ligands.
Microwave-assisted synthesis of DPCTS and BDPCTS
These ligands were prepared by the condensation of 5,7,8,9-Tetrahydropyrazolo[4,3-b]carbazol-
6-[1H]-one [TPC] and 9-Benzyl-5,7,8,9-tetrahydropyrazolo[4,3-b]carbazol-6-[1H]-one [BTPC]
with thiosemicarbazide in 1:1 molar ratio in the ethanolic medium as illustrated in Scheme 3.
After refluxing the contents by using microwave technique, obtained thiosemicarbazones were
separated out as crystalline solids. These were dried and purified by recrystallization, from the
same solvent. The resulting colored precipitate were recrystallized with alcohol and dried under
vacuum. The analytical data and the yields are reported in Table 1.
S
H
N
H
NH2-NH-C-NH2
N
N
N
N
N
H
hydrazinecarbothioamide
O
N
H
HN
C S
H2N
5,7,8,9-tetrahydropyrazolo[4,3-b]
carbazol-6(1H)-one
(Z)-2-(8,9-dihydropyrazolo[4,3-b]carbazol-6(1H,5H,7H)-
ylidene)thiosemicarbazone

DPCTS
S
H
N
H
N
NH2-NH-C-NH2
N
N
N
N
H
O
N
H
HN
C S
H2N
9-benzyl-5,7,8,9-tetrahydropyrazolo (Z)-2-(9-benzyl-8,9-dihydropyrazolo[4,3-b]
[4,3-b]carbazol-6(1H)-one
carbazol-6(1H,5H,7H)-ylidene)thiosemicarbazone
BDPCTS
Scheme 3. Structure of thiosemicarbazone based ligands
Synthesis of cadmium (II) complexes
The calculated amounts (0.5 g, 2.73×10-3 M) of dihydrated CdCl2 in 5 mL of anhydrous
methanol were added to the methanolic solution of the ligands [DPCS] (1.54 g), [BDPCS] (2.03
g), [DPCTS] (1.63 g)and [BDPCTS] (2.13 g) in 1:2 stoichiometric ratios and the reaction
mixtures were refluxed for 5−6 min in microwave oven. Small quantities of petroleum ether
(60−80 ℃) were then added whereupon new complexes were separate out. They were filtered off
washed (3×10 mL) with petroleum ether and finally dried. The analytical data and the yields are
reported in Table 1.
Synthesis of tin(II) complexes
The weighed amounts of SnCl2.2H2O (0.5 g, 2.21×10-3M) in ~5 mL of methanol were added to
the methanolic solution of the ligands [DPCS] (1.25 g), [BDPCS] (1.65 g), [DPCTS] (1.3 g) and
[BDPCTS] (1.72 g) in 1:2 stoichiometric ratios and the reaction mixture were refluxed for 4−6
min in microwave conditions. The precipitated complexes were filtered and washed (3×10 mL)
with a mixture of methanol and petroleum ether and recrystallized with ethanol and finally dried.
The analytical data and the yields are reported in Table 1. Proposed structures of Cd and Sn
complexes are shown below.
X
H
N
N
NH2
Cl
M
N
Y C
N
H
NH
H
HN
N
C Y
Cl
N
H2N
N
X
N
H
.2H2O

Where, M = Cd(II) and Sn(II), X= -CH2/-CH2CH2C6H5, Y= O/S
Proposed structures of complexes.
3-D structure of the Cd(II) complex (here crystalline water molecules are not shown).
Results and discussions
Elemental analysis and conductance measurements
Elemental analyses of Cd(II) and Sn(II) complexes of Schiff-base ligands are reported in Table
1. All the compounds were reacted in 1:2 stoichiometry, which indicating metal-ligand
stoichiometry of resultant mononuclear complexes and ligands behave as bidentate towards the
metal ions. The molar ionic conductance values of mononuclear complexes of cadmium and tin
metals in DMF are low which are suggesting non-electrolytic nature of these metals chelates [56]
as well as is also signifying that both chloride ions are present in coordination sphere.
Magnetic moment
The natures of the ligand field around the metal complexes were deduced from the electronic
spectra and magnetic moment data of the complexes. The Cd(II) and Sn(II) complexes are
diamagnetic at room temperature, attributed to the low spin octahedral structures and results are
reported in Table 2.

Table 1
Physical data and analytical properties of ligands and their corresponding complexes.
Colour
Yellow
Brown
Elemental analysis, Found/(Calcd.) %
mp
(℃)
MW, Found/
(Calcd.)
Yield
(%)
89
Time
Min.
6
Compounds
C
H
N
O
S
Cl
-
M
-
59.91
(59.6)
67.77
(67.3)
56.91
(56.6)
61.77
(64.9)
42.60
(42.0)
53.54
(53.0)
41.09
(41.1)
49.08
(50.1)
42.09
(42.6)
51.75
(51.0)
40.09
(40.9)
49.45
(49.0)
5.79
(5.00)
5.01
(5.41)
4.79
(4.73)
4.01
(5.19)
4.92
(4.11)
4.09
(4.27)
3.92
(3.95)
3.44
(4.01)
4.60
(4.08)
4.98
(4.09)
3.52
29.56
(29.7)
26.81
(22.5)
28.56
(28.1)
25.81
(21.6)
21.72
(21.4)
16.98
(17.9)
20.49
(20.6)
16.32
(16.8)
21.90
(21.2)
20.34
(20.9)
20.09
(20.4)
20.99
(20.2)
(5.6)
250-52 279
(282.30)
262-65 379
(372.17)
130-35 298
(298.37)
146-50 389.15
(388.15)
290-92 780.09
(783.93)
DPCS
(4.3)
-
-
90
87
92
92
89
90
91
96
92
90
89
5
6
6
6
6
5
6
5
4
5
5
BDPCS
Light
-
-
10.34
(10.5)
8.63
-
-
DPCTS
yellow
Yellow
brown
-
-
BDPCTS
(8.25)
Chilly red
(8.1) -
9.92
13.60
[Cd(DPCS)2Cl2]
[Cd(BDPCS)2Cl2]
[Cd(DPCTS)2Cl2]
[Cd(BDPCTS)2Cl2]
[Sn(DPCS)2Cl2]
[Sn(BDPCS)2Cl2]
[Sn(DPCTS)2Cl2]
(9.04) (14.3)
7.34 11.65
(7.62) (12.0)
9.92 13.66
Red
(6.8) -
304
932.4
( 936.74 )
Light
yellow
Brown
(3.9) 7.92
210-12 824
(816.05)
245-47 997.98
(995.70)
(7.86) (8.69) (13.7)
(3.0) 6.43 7.32 12.43
(6.40) (7.13) (11.2)
Orange
Yellow
(8.1) -
8.09
(8.97) (15.0)
7.66 13.45
(7.57) (12.6)
8.52 12.66
16.60
302
789
(790.22)
924.02
(972.44)
(6.4) -
305
Reddish
brown
[Sn(BDPCTS)2Cl2] Brown
(3.8) 7.52
280-85 820
(822.35)
959
(1004.57)
(3.92)
3.62
(3.95)
(7.78) (8.62) (14.4)
(3.1) 6.98 7.44 13.34
(6.37) (7.32) (12.2)
303
Note: Crystalline water molecules are not shown in chemical formulae.

Table 2
Magnetic moment, molar conductivity and electronic spectral data of the complexes.
Complex
µeff (BM)
Λ (Ω-1cm2mol-1) λmax(nm) Assignments
Cd(DPCS)2Cl2].2H2O
Diamagnetic
44
38
41
47
27
25
24
21
21
345
256
352
260
347
258
358
264
380
270
387
275
389
287
325
275
325
275
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
[Cd(BDPCS)2Cl2].2H2O
[Cd(DPCTS)2Cl2].2H2O
[Cd(BDPCTS)2Cl2].2H2O
[Sn(DPCS)2Cl2].2H2O
[Sn(BDPCS)2Cl2].2H2O
[Sn(DPCTS)2Cl2].2H2O
[Sn(BDPCTS)2Cl2].2H2O
[Sn(BDPCTS)2Cl2].2H2O
IR Spectra
Diamagnetic
Diamagnetic
Diamagnetic
Diamagnetic
Diamagnetic
Diamagnetic
Diamagnetic
Diamagnetic
The IR spectra provide valuable information regarding the nature of the functional group
attached to the metal atom. The IR spectral results of Schiff bases and their metal chelates are
tabularized in Table 3, which indicates that Schiff bases are coordinated to metal atom in two
ways, thus ligand acting in bidentate manner. The IR spectra of free ligands were compared with
those of the complexes in order to confirm the coordination of semi and thiosemicarbazones. The
IR spectra of the free Schiff base ligands show a strong band in the region 1690–1580 cm−1 that
is characteristic of the azomethine group [57, 58]. Coordination of the Schiff bases to the metal
through the nitrogen atom is expected to reduce the electron density in the azomethine
frequency. The band due to azomethine nitrogen υ(C=N) shows a modest decrease in the stretching
frequency for the complexes and is shifted to lower frequencies, appearing around 1688-1578
cm−1, which indicates the involvement of azomethine nitrogen in coordination to the metal ions
[59]. The free ligand must exhibit thiol
thione tautomers, which is brought about by the
presence of thioamide (−NH/C=S) functional group. The υ(C=S) band in the range of 1156-945
cm−1 are present, indicating that the free ligands remain as the thione tautomer in the solid state.
The v(S-H) band at ~ 2570 cm−1 is absent in the IR spectra of the ligands and the presence of v(N-H)

band at ~3350 cm−1 indicating that the free ligand in the thione form in coordination [60]. The
υ(N−H) band present in the free ligand still observed in any metal complex, indicating
deprotonation not proceed of the ligand in situ to form the thiol tautomers for the formation of
metal complexes, thus supporting the suggestion of coordination through the thione sulfur. A
doublet appears at 3350−3200 cm−1 in the free ligands remains at almost the same positions in
the metal complexes suggesting that the terminal amino group is not involved in the chelation
[61]. The v(C=S) [62] and v(C=O) bands are still present in the complexes but shifted to a lower
wave number indicating that the sulfur and oxygen also involved in coordination. All complexes
shows extra bands in the 548−532 cm−1, 490−415 cm−1 and 405−332 cm−1 regions assigned to
v(M-N), v(M-O/S) and v(M-Cl) stretching vibrations, respectively not in the spectra of their
uncomplexed Schiff bases, thus further confirming complexation [63-68].
Table 3
Vibrational (υ cm-1) spectral data of Schiff bases and their complexes.
Compounds
υC=Cstr. υC=O/S υC=Nstr. υN−Hstr. υM-Nstr. υM-S/O υM-Cl
DPCS
1505
1548
1495
1545
1486
1478
1543
1540
1578
1495
1620
1495
1678 1688
1675 1645
1156 1678
1023 1640
1645 1642
1655 1628
3350
3350
3350
3350
3312
3318
3350
3316
3312
3318
3311
3360
-
-
-
BDPCS
-
-
-
DPCTS
-
-
-
BDPCTS
-
-
-
[Cd(DPCS)2Cl2].2H2O
[Cd(BDPCS)2Cl2].2H2O
[Cd(DPCTS)2Cl2].2H2O
[Cd(BDPCTS)2Cl2].2H2O
[Sn(DPCS)2Cl2].2H2O
[Sn(BDPCS)2Cl2].2H2O
[Sn(DPCTS)2Cl2].2H2O
[Sn(BDPCTS)2Cl2].2H2O
535
532
538
534
541
542
548
540
440
478
450
415
490
423
484
415
395
354
405
333
344
354
332
340
945
1635
1008 1610
1655 1640
1615 1635
1040 1628
980
1578
Electronic Absorption Spectra
The electronic spectral data of all the complexes are reported in Table 2. In the UV region, an
intense bands for diamagnetic complexes (Cd and Sn) near 380−395 and 270−290 nm, which are

also present in the free ligand is assigned to π−π* transitions from the benzene ring and the
double bond of the azomethine group. The bands in the range 345−358, 256−264 nm are due to
n−π* transitions of nonbonding electrons present on the nitrogen of azomethine group in the
Schiff base. In the tin and cadmium complexes, these bands undergo bathochromic as well as
hypsochromic shift due to coordination of the Schiff base ligand to metal ion [69-72].
1HNMR Spectra
The NMR technique is highly useful to prove the structure of the compounds. The above
bonding patterns are further supported by the proton nuclear magnetic spectral studies of the
1
ligand and their corresponding complexes. The HNMR spectra of the free ligands and their
cadmium and tin complexes were recorded in DMSO-d6 and data are tabulated in Table 4. The
NH2 group next to thione and keto group gives a sharp singlet at δ 7.6 and 7.5 ppm in the free
ligands, respectively and remains unchanged in their respective complexes [73]. It shows that
NH2 group is not taking part in the complexation. The signal due to N−H proton at δ 7.0−7.9
ppm in the spectra of the metal chelates i.e., a downfield shift of the –NH group signal occurred
and it strictly certain with the observed vibrational spectra, which suggested that deprotonation
do not occur and it has also shown keto/thione form of the ligands. This can be correlated to a
decrease in electron density and a deshielding of proton because of the participation of the
adjacent carbonyl/thiocarbonyl and azomethine group upon coordination [74-76] whereas this -
NH proton signal of ligands was appear in spectra at 7.01 to 7.1. The multiplets in the region of δ
7.3–8.2 ppm were assigned to aromatic ring protons, which also shifted downfield in the
complexes. The indazole –NH signal was appear at δ 12.4 ppm and it remains at the same
position in the spectra of the metal complexes. The multiplets of signals in the range of δ 1.7−2.8
ppm were observed in the ligands assigned to the methylene protons of ring attached with the
azomethine group, shifted downfield in the spectra of the corresponding complexes on account
of its deshielding which is attributed to the donation of the lone pair of electrons of the
azomethine nitrogen to the metal ion.

Table 4
1H NMR spectral data (ꢀ ppm) of Schiff bases and their complexes.
Compound
δ (N-H) indazole δ (C-H) pyrrole δ (N-H) indole δ (Ar-CH2)
δ (N-H) δ (Ar-H)
1.7-2.8 (t/m) 7.1 (s) 7.8-8.0 (s)
1.6-2.3 (s/m) 7.1 (s) 7.3-8.1 (m)
1.7-2.8 (t/m) 7.0(s) 7.8-8.0 (s)
1.6-2.3 (s/m) 7.0 (s) 7.3-8.1 (m)
1.8-2.8 (t/m) 7.6 (s) 7.8-8.0 (s)
1.7-2.3 (t/m) 7.9 (s) 7.3-8.1 (m)
1.8-2.8 (t/m) 7.7 (s) 7.8-8.0 (s)
1.7-2.3 (t/m) 7.7 (s) 7.3-8.1 (m)
1.7-2.6 (t/m) 7.8 (s) 7.6-8.2 (s)
1.7-2.6 (t/m) 7.9 (s) 7.6-8.2 (s)
1.7-2.6 (t/m) 7.8 (s) 7.6-8.2 (s)
1.7-2.6 (t/m) 7.9 (s) 7.6-8.2 (s)
δ (NH2)
7.5 (s)
7.5 (s)
7.6 (s)
7.6 (s)
7.5 (s)
7.5 (s)
7.6 (s)
7.6 (s)
7.5 (s)
7.5 (s)
7.6 (s)
7.6 (s)
DPCS
12.4 (s)
12.4 (s)
12.4 (s)
12.4 (s)
12.4 (s)
12.4 (s)
12.4 (s)
12.4 (s)
12.3 (s)
12.3 (s)
12.3 (s)
12.3 (s)
8.30 (s)
8.17 (s)
8.22(s)
8.17 (s)
8.30 (s)
8.17 (s)
8.22 (s)
8.17 (s)
8.24 (s)
8.24 (s)
8.24 (s)
8.24 (s)
10.0 (s)
10.0 (s)
10.1 (s)
10.1 (s)
10.0 (s)
10.0 (s)
10.1 (s)
10.1 (s)
11.6 (s)
11.6 (s)
11.6 (s)
11.6 (s)
BDPCS
DPCTS
BDPCTS
[Cd(DPCS)2Cl2].2H2O
[Cd(BDPCS)2Cl2].2H2O
[Cd(DPCTS)2Cl2].2H2O
[Cd(BDPCTS)2Cl2].2H2O
[Sn(DPCS)2Cl2].2H2O
[Sn(BDPCS)2Cl2].2H2O
[Sn(DPCTS)2Cl2].2H2O
[Sn(BDPCTS)2Cl2].2H2O

119Sn NMR
119Sn NMR spectra can be used as an indicator of coordination number of tin atom. The
119Sn NMR spectrum of the [Sn(DPCS)2Cl2] complex shows a sharp signal at δ − 544 ppm.
The chemical shifts are in the range for six-coordinate tin compounds [77]. This chemical
shift also shows that significant effect on the shielding of the tin nucleus by the ligand
donation with high coordination and presence of s-orbital electron density.
Thermal Analysis
Thermal study implies that the complexes are more stable than the ligand, since the
ligands start to decompose at lower temperature compared to the complex [78]. The thermal
studies are in agreement with elemental analysis for the presence of crystalline water
molecules. More over the lattice water will be lost at lower temperature compared to the
coordinated water. After the elimination of lattice water, usually the decomposition of the
ligand occurs. It has been observed that Sn(II) complex shows a loss amount to 4.12%
(4.37% calc.) in the weight between 115−160 ℃, which is indicating the loss of two lattice
water molecules. All the complexes of tin were thermally stable and show multi stage
decomposition. The removal of coordinated chlorine occurs at the temperature range
160−250 ℃. Above 250 ℃ the ligand starts to decompose, the organic part in all the
complexes starts to decompose above 160 ℃. The TG curve in the 160−480 ℃ range
suggests that the loss in the weight corresponds to the remaining ligand molecule. The mass
loss (34.65%) indicates that the formation of the residue left as SnO2 and SnO. Apart from
providing valuable insight into the thermal stability of the tin complex, this study also
supported the formation of the complexes. The trace of thermo gravimetric analyses of the
complex is shown in Fig.1. It is characterized by weight losses until 500 ℃.
Fig. 1. Thermogram of [Sn(DPCS)2Cl2]. 2H2O complex.

Mass Spectra
The mass spectrum of the ligand DPCTS is shown in Fig. 2, the peak at m/z =298 stand
for the molecular ion peak which coincide with its formula weight. The proposed
fragmentation pattern of the ligand is given below. The ligand spectrum shows M+− 1 and
M++1 peaks which are characteristics of amine group. Loss of one of the amino hydrogen
atom of thiosemicarbazone gives a moderately intense M+−1 peak; this effect is more
pronounced in amino group because of the better resonance stabilization of ion fragment by
the nitrogen. This molecular ion peak also has the good agreement with nitrogen rule of
molecular fragmentation as well as their calculated value of molar mass = 298. The measured
molecular weights were consistent with expected values, and the mass spectrum of the
complex is shown in Fig. 3. The molecular ion peak of Cd(II) complex locates at m/z = 824
which is good agreement with the structural formula suggested by elemental analysis,
spectral, and magnetic studies. The mass fragmentation pattern of cadmium complex with
thiosemicarbazide ligand [79] is given below.
X-ray diffraction pattern of Sn complexes
In order to ascertain the crystal lattice of these compounds [Sn(DPCTS)2Cl2].2H2O has been
recorded. The observed inter planar spacing values (‘d’ in Å) have been measured from the
diffractogram of the compound and the miller indices h, k and l have been assigned to each d
value and 2θ angles are reported in Table 5. The results show that the tin complexes belongs
to ‘Tetragonal’crystal lattice system having unit cell parameters as a = 15.859, b = 15.859, c
= 15.95 α = β = γ = 90°, respectively, max deviation of 2θ = 0.043.

Fig. 2. Mass spectrum of ligand DPCTS.

.+
H
N
H
N
N
N
N
N
H
- NH3 17 m/z
C S
N
N
H
HN
N
m/z = 281
(84 %)
m/z = 298
(69 %)
Molecular ion peak
S
C
H2N
- CS, 44 m/z
-N2, 28 m/z
H
N
N
N
N
H
H2N
m/z = 239
(M+1) =
N
N
H
H3C
(83%)
HN
- N2, 28 m/z
C S
H2N
m/z = 270
(base peak)
100 %
H
N
N
N
H
m/z = 209
(65%)
- N2CH2, 42 m/z
N
H
m/z = 167
(38%)
The suggested mass fragmentation pattern of ligand DPCTS.

Fig. 3. Mass spectrum of the [Cd(DPCTS)2Cl2].2H2O

NH2
NH2
Cl
C
C
S
NH
N
S
NH
N
N
N
HN
HN
- (Cl2, 71 (m/z)
(M+- 1)
HN
N
HN
N
Cd
NH
Cd
NH
N
N
NH
NH
Cl
HN
HN
S
S
C
C
H2N
m/z = 824
H2N
2H2O
.2H2O
m/z = 752
(Molecular ion peak, 32 %)
(2H2O, m/z = 36
(N2 + H2), m/z = 30
Base peak (100 %)
NH2
C
S
NH
N
HN
NH2
N
Cd
NH
Cl
C
N
S
NH
N
N
NH
HN
HN
S
HN
N
C
Cd
NH
N
.2H2O
H2N
NH
m/z = 722
76 %
HN
Cl
S
C
H2N
(N2 + H2), m/z = 30
m/z = 777
(34.4%)
NH2
C
S
NH
HN
N
Cd
N
NH
HN
S
C
H2N
.2H2O
m/z = 692
(39 %)
(C2H4), m/z = 28
NH2
C
C
N
N
S
S
NH
HN
HN
( NH3 + NH2), m/z = 31
Cd
N
N
Cd
N
NH
NH
N
S
C
HN
S
C
m/z = 631
(74 %)
H2N
m/z = 664
(49 %)
. 2H2O
. 2H2O
The suggested fragmentation pattern of [Cd(DPCTS)2Cl2]. 2H2O complex

Table 5
X-ray powder diffraction data for the compound [Sn(DPCTS)2Cl2]. 2H2O.
2θ (Obs)
2θ (Calcd)
Intensity
h
k L d-spacing
°A(Obs)
26.353
30.795
32.346
33.721
36.568
37.812
43.221
46.015
54.269
57.092
63.555
66.809
70.322
71.674
73.380
76.008
80.002
26.310
30.833
32.312
33.688
36.566
37.852
43.201
46.001
54.239
57.100
63.567
66.799
70.364
71.667
73.393
76.015
79.985
558.44
516.74
422.56
1136.37
730.77
480.82
511.71
650.85
371.54
269.76
261.81
217.61
228.56
205.07
220.30
262.44
248.28
3
5
4
0
4
3
3
6
2
9
9
8
3 2 3.379
1 2 2.901
1 4 2.765
0 6 2.655
1 5 2.455
0 6 2.377
0 7 2.091
2 5 1.970
2 9 1.688
0 4 1.611
1 6 1.462
4 7 1.399
10 4 5 1.337
9
3
1 8 1.315
0 12 1.289
10 6 5 1.251
3 13 1.198
2
Refined Values of a = 15.859; b = 15.859; c = 15.95, α = β = γ = 90° (Tetragonal lattice)
Biological studies
The structures of all complexes have been confirmed by the various physical methods and also
supported by spectroscopic data. Virtually, ligand and their metal complexes were tested for their
antimicrobial study to prove object of this study.
Anti-bacterial activity
The antibacterial activity of the ligands and their metal complexes has been screened against two
bacteria and results are presented in Fig. 4. For the evaluation of degree of inhibitory effects on the
growth of a wide spectrum of microorganisms antibacterial activity was performed against

(Bacillus subtilis and Escherichia coli) bacteria. In order to compare the results obtained the
ciprofloxacin (10 μg/mL) was used as standard drug. Determination of the antibacterial activity
was carried out by the paper-disc plate method. The compounds were dissolved in DMF at 500
and 1000 ppm concentrations. All the Whatman No. 1 paper with a diameter 5 mm were soaked
in these solutions. These discs were placed on the appropriate nutrient medium previously seeded
organisms in Petri dishes and stored in an incubator at 37 ℃. The inhibition zone around each
disc was measured (in mm). The results clearly indicate that the ligands of thiosemicarbazone
moiety derived from the parent heterocyclic compound are more active than the semicarbazones.
Almost all the complexes were found to be more active against all the organisms used than the
ligands themselves. The enhanced antimicrobial activity of the metal chelates over their
corresponding chelating agents may be explained by the chelation theory [80, 81]. Chelation reduces
the polarity of the metal ion mainly because of partially sharing of its positive charge with the donor
groups and possible π-electron delocalization within the whole chelate ring. This chelation increases
the lipophilic nature of the metal complex which subsequently favors its permeation through the lipid
layer of the cell membrane of the microorganism and thereby, impairing normal cell process. Since
the plasma membrane is in general more permeable to non-polar compounds than to polar
compounds, it is natural to hypothesize that the more lipid-soluble compounds are more toxic, simply
because they enter the cell more rapidly.
B. Subtilis, Zone of inhibition (in mm), 24 h (Conc. in ppm) 500
B. Subtilis, Zone of inhibition (in mm), 24 h (Conc. in ppm) 1000
E. Coli, Zone of inhibition (in mm), 24 h (Conc. in ppm) 500
E. Coli, Zone of inhibition (in mm), 24 h (Conc. in ppm) 1000
33
3030
28
26
25
25 25
24
21 21 21
19
16
24
23
23
21
21
21
20 20
20
19
19
19 19
17 17
17 17
16
14
16
16
15
14
15
13
10
14
14
12
11
12
11
1111
8
10
8
6

Fig. 4. Antibacterial screening data for the ligands their Cd(II) and Sn(II) complexes.
.Anti-fungal activity
Bio efficacies of synthesized compounds were checked in vitro. The in vitro anti-fungal
activities of the ligands and their complexes have been evaluated against two pathogenic fungi,
Aspergillus niger and Aspergillus flavus using fluconazole as standard by disc diffusion
technique and results are shown in Fig. 7. The discs were stored in an incubator at 37 ℃.
Percentage inhibition = 100(C−T)/C
Where, C is the diameter of fungal growth on the control plate, and T is the diameter of fungal
growth on the test plate. The inhibition zone around each disc was measured (in mm) after 96 h.
A. Niger, Zone of inhibition (in mm), 96 h (Conc. in ppm) 100
A. Niger, Zone of inhibition (in mm), 96 h (Conc. in ppm) 200
A. Flavus, Zone of inhibition (in mm), 96 h (Conc. in ppm) 100
A. Flavus, Zone of inhibition (in mm), 96 h (Conc. in ppm) 200
31
30
28
27
27
24 24 24
26 26
21
25
25
24
23
23
23
22
21
19
21
19
21
18
21
20
19
18
18
18
16
14
16
14
16
16
13
16
15
14
12 12
15
12
14
1313
13
12 1212
11
Fig. 5. Antifungal screening data for the ligands their Cd(II) and Sn(II) complexes.
.
Conclusions
This paper describes the preparation and characterization of three new mononuclear Cd(II),
and Sn(II) complexes based bidentate carbazole derived ligand and investigating their spectral
studies. The procedure is simple and efficient towards various aryl ketones. The diamagnetic
complexes are non-electrolytic nature on the basis molar ionic conductance analyses. The
spectral studies reasonably proved that complexation of the metal and ligand took place. The
ligand coordinates to the metal centers via N and O/S donor atoms. All the above investigations

have revealed hexa-coordinated stereochemistry around the metal ions. The resulting products
are lipophilic in nature. Thermal study implies that the complexes are more stable than the
ligand, since the ligands start to decompose at lower temperature compared to the complex
Changes in concentration influence the antimicrobial property. These compounds, even at lower
concentration, inhibit the growth of microorganisms.
Acknowledgement
We are thankful to Professor Aditya Shastri, Vice Chancellor of Banasthali Vidyapith for
kindly extending the facilities of ‘‘Banasthali Centre for Education and Research in Basic
Sciences” sanctioned under CURIE programme of the Department of Science and Technology,
New Delhi.
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