Synthesis of some organometallic complexes of Ti(IV)/Zr(IV) involving sulfur containing schiff base ligands: Spectral, electrochemical, surface morphology, and antimicrobial studies

Article abstract of DOI:10.1080/15533174.2013.862826

The reactions of bis(cyclopentadienyl)titanium(IV)/zirconium(IV) dichloride with Schiff base derived by condensing thiophene-2-carboxaldehyde (tc), pyridine-2-carboxaldehyde (pc), and 5-methylthiophene-2-caroxaldehyde (mtc) with sulfamethoxazole (sm) have

Full text of DOI:10.1080/15533174.2013.862826

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Synthesis of Some Organometallic Complexes of Ti(IV)/
Zr(IV) Involving Sulfur Containing Schiff Base Ligands:
Spectral, Electrochemical, Surface Morphology, and
Antimicrobial Studies
J. Pushparajana & M. sivasankaran Naira
a Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli, India
Accepted author version posted online: 15 Apr 2015.
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To cite this article: J. Pushparajan & M. sivasankaran Nair (2015) Synthesis of Some Organometallic Complexes of Ti(IV)/
Zr(IV) Involving Sulfur Containing Schiff Base Ligands: Spectral, Electrochemical, Surface Morphology, and Antimicrobial
Studies, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 45:10, 1549-1557, DOI:
10.1080/15533174.2013.862826
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 1549–1557
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.862826
Synthesis of Some Organometallic Complexes of Ti(IV)/Zr
(IV) Involving Sulfur Containing Schiff Base Ligands:
Spectral, Electrochemical, Surface Morphology,
and Antimicrobial Studies
J. PUSHPARAJAN and M. SIVASANKARAN NAIR
Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli, India
Received 3 July 2013; accepted 2 November 2013
The reactions of bis(cyclopentadienyl)titanium(IV)/zirconium(IV) dichloride with Schiff base derived by condensing thiophene-2-
carboxaldehyde (tc), pyridine-2-carboxaldehyde (pc), and 5-methylthiophene-2-caroxaldehyde (mtc) with sulfamethoxazole (sm)
have been studied in refluxing tetrahydrofuran under nitrogen atmosphere. The complexes of the type [Cp2MCl(L)]Cl (L D tc-sm,
pc-sm, and mtc-sm; M D Ti/Zr) have been isolated and have been characterized using elemental analyses, molar conductance, mass,
1H NMR, 13C NMR, IR, UV-Vis, CV, TGA, powder XRD, and SEM. The results show that the Schiff base ligands are coordinated
to the metal ions in a bidentate manner. Antimicrobial studies were conducted to assess growth inhibition potential of complexes
and ligands against various fungal and bacterial strains.
Keywords: Schiff base, IR, NMR, CV, SEM
Introduction
investigation on Schiff base metal complexes involving sulfa-
methoxazole and heterocyclic aldehydes are sparse. The
Metal based drugs have been used in medicine for many present study describes the synthesis and characterization of
centuries, but very often only in an empirical fashion. The three novel Schiff base ligands viz. thiophene-2-carboxaldi-
biological application of organometallic complexes of the mine-sulfamethoxazole (tc-sm), pyridine-2-carboxaldimine-
fourth group transition metals have been extensively stud- sulfamethoxazole (pc-sm), and 5-methylethiophene-2-car-
ied.[1–6] The bis(cyclopentadienyl)titanium/zirconium com- boxaldemine-sufamethoxazole (mtc-sm) and the complexes
plexes can be viewed as potential anticancer agents owing to containing these three ligands and bis(cyclopentadienyl) tita-
their ability to organize organic ligands in three-dimensional nium(IV)/zirconium(IV) dichloride.
space to target receptors, coupled with the redox properties
of the tunable metal centre and lability of the metal–carbon
bonds.[7–9] Schiff bases are considered as a very important
class of organic compounds which have wide applications in
Experimental
the analytical, catalytic, and biological fields. Metal com-
plexes of these ligands are sometimes more effective than
the free ligands.[10–14] It has also been observed that a small
structural change in the ligand may lead to the enhanced
activity of the metal complexes. Among the various classes
of biologically active coordination compounds, complexes
with sulfonamides constitute an important class of antimi-
crobial agents.[15,16] A wide range of biological activities of
sulfamethoxazole derivatives include pharmacological prop-
Materials and Reagents
All the reactions were carried out strictly under anhydrous
condition under N2 atmosphere. The aldehydes, sulfamethox-
azole, bis(cyclopentadienyl)titanium(IV)dichloride and bis
(cyclopentadienyl)zirconium(IV)dichloride were obtained
from Sigma-Aldrich and used without further purification.
Tetrahydrofuran was dried by sodium wire overnight and
then refluxed until it gave a blue color with benzophenone.
All other reagents and solvents were purchased from
commercial sources and were of analytical grade.
erties such as antibacterial, anticancer, anti-HIV activity,
[17]
and agrochemical activities.
The literature reveals that
Synthesis of Schiff Base Ligands
Address correspondence to M. Sivasankaran Nair, Department
of Chemistry, Manonmaniam Sundaranar University, Tirunel-
veli-627 012, India. E-mail: msnairchem@rediffmail.com
Sulfamethoxazole (5 mmol) dissolved in dry MeOH (50 mL)
in a three-necked 100 mL R.B flask under N2 atmosphere

1550
Pushparajan and Sivasankaran Nair
1550

Synthesis of Some Organometallic Complexes
1551
Table 2. 1H and 13C NMR spectral data of Schiff base ligands and their complexes
Ligand/complex
tc-sm
Nucleus
0
ÀÀC5H5
Aromatic (ÀÀCH)
ÀÀCHHN
7.17
157.52
7.3
159. 52
7.32
160.11
7.05
150.41
7.26
152.32
7.22
153.21
7.15
158.13
7.32
ÀÀNH
1H
13C
1H
2.32
12.38
2.34
12.39
2.36
12.38
2.32
12.38
2.31
12.39
2.33
12.38
2.3
12.38
2.31
12.39
2.35
—
—
7.2–7.9
116.2–152.6
7.25–7.85
116.5–152.8
7.35–7.92
116.3–152.5
7.5–7.75
117.1–153.0
7.53–7.7
117.0–153.2
7.52–7.89
122.3
7.52–7.68
116.6–152.6
7.5–7.7
116.8–152.6
7.54–7.77
116.5–152.8
8.6
—
8.58
—
8.59
—
8.72
—
8.72
—
8.73
—
8.78
—
8.8
—
[(C5H5)2TiCl(tc-sm)]Cl
[(C5H5)2ZrCl(tc-sm)]Cl
pc-sm
6.59
114.5
6.68
114.5
—
13C
1H
13C
1H
13C
1H
—
[(C5H5)2TiCl(pc-sm)]Cl
[(C5H5)2ZrCl(pc-sm)]Cl
mtc-sm
6.54
115.4
6.62
115.6
—
13C
1H
13C
1H
13C
1H
—
[(C5H5)2TiCl(mtc-sm)]Cl
[(C5H5)2ZrCl(mtc-sm)]Cl
6.57
114.3
6.58
114.3
13C
1H
160.43
7.36
161.12
8.79
—
13C
12.4
was mixed with 5 mmol of thiophene-2-carboxaldehyde (tc- Synthesis of Ti(IV))/Zr(IV) Schiff Base Complexes
sm)/pyridine-2-carboxaldehyde (pc-sm)/5-methylthiophene-
To a refluxing solution of bis(cyclopentadienyl)titanium(IV)
dichloride (2 mmol) in 40 mL anhydrous tetrahydrofuran
under N2 atmosphere in a three neck 100 mL R.B flask,
2 mmol of the ligand (tc-sm, pc-sm, and mtc-sm) was added
in 1:1 ratio and the reaction mixture was stirred and then
refluxed for 36 h. The reddish brown to dark brown colored
complex so obtained was filtered, washed with anhydrous
tetrahydrofuran and ether and then dried in vacuo over anhy-
drous CaCl2. In the case of Zr(IV) Schiff base complexes
reflection was not employed otherwise all the reaction condi-
tions are same. An orange to reddish brown colored product
2-carboxaldehyde (mtc-sm) and KOH pellets (5 mmol). The
reaction mixture was vigorously stirred at room temperature
for15 minutes and then refluxed at 70–80ꢀC for 8 h. The yel-
low solution was reduced to one-third of its original volume
by rotary evaporation. The concentrated filtrate thus
obtained was poured into diethylether, when a pale yellow to
yellow precipitate was formed. This was collected by vacuum
filtration and washed several times with anhydrous ether and
then dried in vacuo over anhydrous CaCl2. The yields of the
isolated ligands were found to be 72–80%.
Fig. 1. 1H-NMR spectrum of tc-sm.

1552
Pushparajan and Sivasankaran Nair
Table 3. IR spectral data of the Schiff base ligands and their complexes (cm¡1
)
Compound
nazo.(CHN)
nring.(CHN)
n (CÀÀS)
n (NÀÀH)
n(C5H5)
n(MÀÀN)
n(MÀÀS)
—
tc-sm
1616
1593
1612
1618
1598
1610
1617
1612
1613
1583
1561
1594
1592
1590
1592
1587
1592
1595
628
624
622
655
654
648
665
689
661
3454
3452
3453
3384
3384
3385
3361
3363
3362
—
—
—
[(C5H5)2TiCl(tc-sm)]Cl
[(C5H5)2ZrCl(tc-sm)]Cl
pc-sm
[(C5H5)2TiCl(pc-sm)]Cl
[(C5H5)2ZrCl(pc-sm)]Cl
mtc-sm
3103
3100
—
3101
3103
—
413
410
534
528
[(C5H5)2TiCl(mtc-sm)]Cl
[(C5H5)2ZrCl(mtc-sm)]Cl
3104
3100
417
412
was formed after 24 h of stirring under nitrogen atmosphere SDT Q 600/V8.3 build 101 thermal analyzer with the condi-
at room temperature.
tions; sample mass 6–8 mg, heating rate 20ꢀC/min and nitro-
gen atmosphere (flow rate 20 mL/min). Powder XRD was
recorded on a Rigaku Dmax X-ray diffractometer with Cu-
Ka radiation (λKa D 1.5406). SEM images were recorded in a
Hitachi SEM analyzer.
Physical Measurements
Elemental analyses were done using a Perkin-Elmer elemen-
tal analyzer. Molar conductance of the complexes was mea-
sured in DMSO (10¡3M) solution using a coronation digital
conductivity meter. IR spectra were recorded in KBr disc on
a JASCO FT/IR-410 spectrometer in the 4000–400 cm¡1
region. The electronic spectra were recorded on a Perki-
Results and Discussion
Characterization of Schiff Base Ligands
nElmer Lambda-25 UV-Visible spectrometer. The mass spec- The Schiff base ligands are soluble in all common organic sol-
tra of the ligands and their complexes were recorded on a vents. The results of elemental analyses (Table 1) of the
JEOL-AccuTOF JMS-T100LC mass spectrometer. The ligands (tc-sm, pc-sm, and mtc-sm) are in good agreement
1H-NMR and 13C-NMR spectra of the ligands and their with those calculated for the suggested formulae. The EI
complexes were recorded in JEOL GSX 400 FT–NMR spec- mass spectra of the ligands (tc-sm, pc-sm, and mtc-sm) show
trometer. Cyclic voltammetric measurements were carried a well-defined molecular ion peak at m/z D 348.10 (R. I. D
out in a Bio-Analytical system (BAS) model CV-50 W elec- 23%), m/z D 343.11(R. I. D 21%), and m/z D 362.87(R. I. D
trochemical analyzer. The three-electrode cell comprises of a 18%). These are consistent with the proposed molecular for-
1
reference Ag/AgCl, auxiliary platinum and working glassy mulae of the ligands. The H-NMR spectra of tc-sm, pc-sm,
electrodes. Tetrabutylammoniumperchlorate was used as and mtc-sm ligands show peaks at 7.17, 7.05, and 7.15 ppm,
supporting electrolyte. Thermal analysis was carried out on respectively (Table 2), characteristic of azomethine[18] proton
Fig. 2. Mass spectrum of [(C5H5)2TiCl(tc-sm)]Cl.

Synthesis of Some Organometallic Complexes
1553
Fig. 3. 1H-NMR spectrum of [(C5H5)2TiCl(tc-sm)]Cl.
(ÀÀCHHNÀÀ). The aromatic ring protons are observed in the methyl group present in the ligands.[20] The IR spectral data
1
7.2–7.9 ppm range.[19] As a representative system, the H- of the Schiff base ligands are given in Table 3. All the ligands
NMR spectrum of the Schiff base ligand tc-sm is shown respectively show strong bands at 1616, 1618, and 1617 cm¡1
in Figure 1. The 13C-NMR spectra (Table 2) of the ligands due to azomethine stretching frequency. The sharp band pres-
(tc-sm, pc-sm, and mtc-sm) show a peak respectively at ent in the region »3300 and »1520 cm¡1 in the IR spectra is
157.52, 150.41, and 158.13 ppm. These are assignable to azo- due to peptide N-H stretching frequency.[19,20] The UV-Vis
methine carbon (ÀÀCHHNÀÀ).[20] In all the Schiff bases the spectra of free ligands exhibit a broad band at 365–375 nm,
peak at 12.38 ppm in 13C-NMR spectrum is due to the which can be assigned to p-p* and n-p* transition of the azo-
methine (>CHN) chromophore. The intense absorption
band observed at higher energy of 225–270 nm is due to the
p -p* transition of the benzene ring of the Schiff base ligands.
Characterization of Metal Schiff Base Complexes
The analytical data of the metal Schiff base complexes are
given in Table 1. The Ti(IV) and Zr(IV) complexes were tend
to be soluble in MeOH, EtOH, DMF, DMSO, and insoluble
in other common organic solvents. The molar conductance
values (Table 1) of metal complexes in DMSO at 10¡3M fall
in the 83–89 ohm¡1cm2mol¡1 range, which is well within
those for the 1:1 electrolites.[21] This demonstrates that the
present complexes have 1:1 electrolitic nature. The data show
that the (Cp)2metal to Schiff base ligand ratio is 1:1 in all the
complex systems. The EI mass spectra of [(C5H5)2TiCl
(tc-sm)]Cl, [(C5H5)2TiCl(pc-sm)]Cl, [(C5H5)2TiCl(mtc-sm)]
Cl, [(C5H5)2ZrCl(tc-sm)]Cl, [(C5H5)2ZrCl(pc-sm)]Cl, and
[(C5H5)2ZrCl(mtc-sm)]Cl show a peak at m/z D 601.11
(11%), 594.31 (14%), 614.11 (19%), 647.06 (14%), 637.35
(17%) and 656.42 (13%), respectively. This indicates that the
complexes are monomeric confirming the (Cp)2metal to
Schiff base ligand ratio to be 1:1. The EI mass spectrum of
[(C5H5)2TiCl(tc-sm)]Cl is shown in Figure 2. The reactions
of bis(cyclopentadienyl)titanium(IV)/zirconium(IV) dichlor-
ide with Schiff bases can be represented by the following
`F1ig. 4. Proposed structure of the metallocene complexes.
equation:

1554
Pushparajan and Sivasankaran Nair
Table 4. Electrochemical data of the complexes
Complex
Epc (V)
Epa (V)
DEp (mV)
Nature
[(C5H5)2TiCl(tc-sm)]Cl
[(C5H5)2ZrCl(tc-sm)]Cl
[(C5H5)2TiCl(pc-sm)]Cl
[(C5H5)2ZrCl(pc-sm)]Cl
[(C5H5)2TiCl(mtc-sm)]Cl
[(C5H5)2ZrCl(mtc-sm)]Cl
–0.6145
¡0.6296
¡0.7820
¡0.7898
¡0.7925
¡0.7990
¡1.0105
¡1.0483
¡1.0075
¡1.0772
¡1.0225
¡1.0520
396
419
225
287
230
253
Quasireversible
Quasireversible
Quasireversible
Quasireversible
Quasireversible
Quasireversible
These peaks which are assignable to azomethine carbon
(ÀÀCHHNÀÀ) show considerable shift in the complexes indi-
cating the involvement of azomethine nitrogen atoms during
coordination.[22] The peak seen at »12.38 ppm in the com-
plexes is due to the CH3 group present in the Schiff base
ligands.
where L D tc-sm, pc-sm or mtc-sm and M D Ti or Zr
IR Spectra
NMR Spectra
The IR spectral data of Ti(IV)/Zr(IV) complexes are given in
1
The H-NMR and 13C-NMR spectral data of the Ti(IV)/Zr Table 3. During complexation, IR stretching frequency for
(IV) complexes are given in Table 2. The 1H-NMR spectrum the free Schiff base ligands respectively at 1616, 1618, and
of [(C5H5)2TiCl(tc-sm)]Cl is shown in Figure 3. The peak in 1617 cm¡1 assigned to azomethine bands are shifted to lower
the 1H-NMR spectra of free ligands tc-sm, pc-sm and mtc-sm frequency indicating the coordination of azomethine nitrogen
respectively at 7.17, 7.05, and 7.15 ppm, characteristic of azo- to the metal ion (Table 3). The sharp band present in the
methine proton(ÀÀCHHNÀÀ) is slightly shifted to downfield region »3300 and »1520 cm¡1 is due to peptide N-H stretch-
in the spectra of Ti(IV)/Zr(IV) complexes. This difference in ing frequencies which are unchanged in the complexes. This
(ÀÀCHHNÀÀ) peak position could arise due to the coordina- shows the absence of the involvement of N-H group during
tion of its neighboring nitrogen atom, which indicates the complex formation.[19,22] The spectra of the metal complexes
metal to coordinate the ligand through azomethine nitrogen show new bands in the 410–420 cm¡1 and 520–540 cm¡1
atom. The aromatic ring protons observed in the 7.2– regions, which may probably be due to the formation of M-S
7.9 ppm range in the ligands are unchanged in the Ti(IV)/Zr and M-N bonds, respectively.[22]
(IV)complexes. The signal in all the Schiff base derivatives at
6.5–6.7 ppm can be assigned to the protons of the cyclopenta-
dienyl ring. The appearance of a single sharp cyclopenta-
Electronic Spectra
dienyl resonance is attributed to the rapid rotation of the
The electronic spectra of Ti(IV)/Zr(IV) complexes (Table 1)
show two absorption bands respectively at 350–365 and
420–430 nm regions, showing the coordination of azome-
thine nitrogen to the metal atom and the charge transfer spec-
cyclopentadienyl ring around the metal ring axis.[22]
The 13C-NMR spectra of Ti(IV)/Zr(IV) complexes
(Table 2) show peak at 157.52, 150.41, and 158.13 ppm for
trum in accordance with the (n-1)d0ns0 electronic
the tc-sm, pc-sm, and mtc-sm ligand systems, respectively.
configuration of the metal atoms.[19,22]
The above discussion shows that the ligands act as neutral
bidentate chelating agents, and the proposed structure of the
Schiff base complexes are shown in Figure 4. These struc-
tures are in good agreement with those reported earlier for
the well-known pentacoordinate structures for titanium and
zirconium complexes.[19,23]
Electrochemistry
The cyclic voltammogram was recorded in MeOH solu-
tion at a scan rate of 100 mVs¡1 in the potential range
C2.0 to –2.0V. The cyclic voltammogram of all the com-
plexes (Table 4) shows a well-defined redox process cor-
responding to the formation of the quasi-reversible
M(IV)/M(III)couple.[24–26] The cyclic voltammogram of
Fig. 5. TGA of [(C5H5)2TiCl(tc-sm)]Cl.
[(C5H5)2TiCl(tc-sm)]Cl
and
[(C5H5)2ZrCl(tc-sm)]Cl

Synthesis of Some Organometallic Complexes
1555
Fig. 6. SEM images of (a) [(C5H5)2TiCl(tc-sm)]Cl; (b) [(C5H5)2TiCl(pc-sm)]Cl, and (c) [(C5H5)2TiCl(mtc-sm)]Cl.
complexes show a redox processes occurring at negative complexes displayed reduction couples at –0.7820 V and
potential with the cathodic peak potential at –0.6145 and –0.7898 V versus Ag/AgCl with the corresponding
–0.6296 V versus Ag/AgCl and anodic peak potential at anodic waves at –1.0075 and at –1.0772 V on the reverse
–1.0105 and –1.0483 V corresponding to the Ti(IV)/Ti scan. The peak separation values (DEp D 225 and
(III) and Zr(IV)/Zr(III) couple, respectively. The peak- 287 mV) indicate totally quasireversible character for the
to-peak separation (DEp D 396 and 419 mV) indicates one electron transfer reaction. Cyclic voltammogram of
quasireversible one electron transfer process. The the [(C5H5)2TiCl(mtc-sm)]Cl and [(C5H5)2ZrCl(mtc-sm)]
[(C5H5)2TiCl(pc-sm)]Cl
and
[(C5H5)2ZrCl(pc-sm)]Cl Cl complexes show one quasireversible redox processes
Table 5. % Zone of inhibition of the synthesized compounds against the growth of bacteria (mm)
Compound
E. coli
K. pneumonia
P. vulgaris
P. aeruginosa
S. aureus
tc-sm
9.0
9.5
9.6
8.6
9.0
8.9
9.1
12.6
12.2
6.3
10.5
10.7
10.5
9.1
9.4
9.6
10.3
14.6
13.8
6.7
6.2
1.8
9.3
9.6
9.5
9.1
9.2
9.6
8.1
11.7
9.8
6.1
4.9
2.2
18.2
7.8
8.0
8.2
8.1
8.9
9.5
9.8
9.9
8.6
8.7
9.1
9.2
9.2
10.2
5.8
5.2
2.3
17.5
[(C5H5)2TiCl(tc-sm)]Cl
[(C5H5)2ZrCl(tc-sm)]Cl
pc-sm
[(C5H5)2TiCl(pc-sm)]Cl
[(C5H5)2ZrCl(pc-sm)]Cl
mtc-sm
[(C5H5)2TiCl(mtc-sm)]Cl
[(C5H5)2ZrCl(mtc-sm)]Cl
(C5H5)2TiCl2
9.2
10.3
10.8
10.6
5.1
4.7
2.1
(C5H5)2ZrCl2
DMF
Ampicillin
5.8
2.0
17.2
17.7
17.3

1556
Pushparajan and Sivasankaran Nair
Table 6. % Zone of inhibition of the synthesized compounds against the growth of fungi (mm)
Compound
A. niger
R. stolonifer
A. flavus
R. bataicola
C. albicans
tc-sm
9.5
9.8
9.6
9.2
9.8
9.7
9.1
9.5
10.1
10.6
10.4
9.5
10.0
9.9
12.8
13.1
13.1
6.6
9.5
9.8
9.9
8.3
8.8
9.1
9.1
9.6
9.5
5.1
6.8
1.8
19.8
9.2
9.8
9.7
8.6
9.1
9.1
9.5
9.8
9.5
6.2
5.2
2.1
18.2
[(C5H5)2TiCl(tc-sm)]Cl
[(C5H5)2 ZrCl(tc-sm)]Cl
pc-sm
[(C5H5)2TiCl(pc-sm)]Cl
[(C5H5)2ZrCl(pc-sm)]Cl
mtc-sm
[(C5H5)2TiCl(mtc-sm)]Cl
[(C5H5)2ZrCl(mtc-sm)]Cl
(C5H5)2TiCl2
9.5
10.8
10.5
10.6
12.3
12.2
6.2
5.8
2.1
18.5
9.6
10.2
12.1
11.8
5.3
4.8
2.6
(C5H5)2ZrCl2
DMF
Ampicillin
4.9
2.3
19.2
18.1
occurring at negative potential and with a peak-to-peak calculated using Scherrer’s formula.[29] The [(C5H5)2TiCl
separation (DEp value) of 230 and 253 mV, respectively. (tc-sm)]Cl, [(C5H5)2TiCl(pc-sm)]Cl, [(C5H5)2TiCl(mtc-
The redox process occurs with the cathodic peak poten- sm)]Cl, [(C5H5)2ZrCl(tc-sm)]Cl, [(C5H5)2ZrCl(pc-sm)]Cl,
tial at –0.7925 and –0.7990 V and anodic peak potential and [(C5H5)2ZrCl(mtc-sm)]Cl complexes have an average
at –1.0225 and –1.0520 V.
crystallite size of 48–61 nm, suggesting that the com-
plexes are in nanocrystalline phase.
The SEM micrographs of the complexes [(C5H5)2TiCl
(tc-sm)]Cl, [(C5H5)2TiCl(pc-sm)]Cl, and [(C5H5)2TiCl(mtc-
sm)]Cl are shown in Figures 6a–c. From the SEM image, it is
observed that grains are well resolved and uniformly distrib-
uted in the [(C5H5)2TiCl(tc-sm)]Cl complex. Moreover, the
average grain size found from SEM shows that the complex
is polycrystalline with nanosized grains. The SEM image of
[(C5H5)2TiCl(pc-sm)]Cl complex shows irregularly shaped
agglomerated particles of submicron size and the presence of
small grains is in micrometer range.
Thermogravimetric Studies
Thermogravimetric studies were made in the temperature
range 25–900ꢀC. Thermal decomposition curves of the com-
plexes of Ti(IV) and Zr(IV) show a similar sequence of two
decomposition steps. All the materials showed very high sta-
bility toward heat. Only a negligible mass loss took place
between 25 and 100ꢀC owing to the removal of entrapped sol-
vent molecules. The materials started degrading after 117ꢀC
and were completely pyrolyzed at around 678ꢀC. The first
step was removal of cyclopentadienyl part and one of the
chloride ions at the range of 220–461ꢀC. This follows the
removal of the remaining organic ligand moieties leaving
metal oxide residue in the second step (476–678ꢀC).
Antimicrobial Activity
The ligands tc-sm, pc-sm, and mtc-sm and their Ti(IV)/Zr
(IV) complexes have been screened for antimicrobial activity
against the bacteria (E. coli, K. pneumonia, P. vulgaris, P. aer-
uginosa, and S. aureus) and the fungal species (A. niger,
R. stolonifer, A. flavus, R. bataicola, and C. albicans) by paper
disc method.[30,31] The concentration for these samples has
been maintained as 1000 ppm in DMF. The results obtained
are explained on the basis of Overtone’s concept and chela-
tion theory.[31,32] The variation in the activity of different
complexes against different organisms depends either on the
impermeability of the cells of the microbes or difference in
ribosomes of microbial cells. The results show that the anti-
bacterial and antifungal activities of ligands may be signifi-
cantly enhanced on chelation with transition metal ions.
Chelation considerably reduces the polarity of the metal ion
because of the partial sharing of its positive charge with the
donor groups and possible p-electron delocalization over the
A representative TGA curve of Ti(IV)-tc-sm complex is
shown in Figure 5. In this a weight loss 26.97% (calcd.
27.59%) in the temperature range 224–446ꢀ C is observed as
a first step due to a loss of cyclopentadienyl moiety and one
of the chloride ions. The second decomposition step of the
complex is observed in the range of 478–672ꢀ C. In this step it
loses the remaining organic ligand moieties leaving a 19.33%
residue. Here the amount of residue obtained is larger than
pure metal oxide. It is difficult to decide on the decomposi-
tion mechanism since the weight of the residue corresponds
to titanium oxide. Because the heating is carried out in nitro-
gen, the residue cannot be pure titanium oxide but most prob-
ably it is carbon or nitrogen containing material.[27,28]
Powder XRD and SEM
Powder XRD pattern of the complexes was recorded chelate ring. Such chelation could increase the lipophilic
over the 2u D 0–80 range. The complexes show sharp character of the central metal atom, which subsequently
crystalline peaks indicating their crystalline nature. The favors the permeation through the lipid layer of cell mem-
average crystallite sizes of the complexes dXRD were brane.[33–35] The antibacterial activity of the complexes

Synthesis of Some Organometallic Complexes
1557
together with parent ligands in DMF has been screened by
the paper disk plate method at 1000 ppm concentration. The
inhibition zone (mm) around each disk was measured after
24 h and the results of these studies are listed in Table 5. The
fungicidal activity of the ligands and the complexes were
evaluated in DMF. The discs were placed on the previously
seeded plates and incubated at 37ꢀC and the diameter of inhi-
bition zone around each disc was measured after 72 h. The
average percentage inhibition was calculated using the
expression: inhibition (%) D 100 (C-T)/C, where C and T are
the diameters of the fungus colony in control and test plates,
respectively and the recorded results are summarized in
Table 6. From the antimicrobial studies it is observed that
the ligands, tc-sm, mtc-sm, and their complexes have shown
good antimicrobial activity towards all the microbes. This
may be due to the presence of heterocyclic sulfur atom in
these ligands, which enhance the antimicrobial activity.[34,36]
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Conclusions
Three new Schiff base ligands tc-sm, pc-sm, mtc-sm, and their
cyclopentadienyl Ti(IV)/Zr(IV) complexes were prepared
and characterized using various analytical techniques. The
NMR, IR, and electronic spectral data show that the Schiff
base ligands coordinate with metal ion through azomethine
nitrogen and heterocyclic nitrogen or sulfur atoms. Interest-
ingly, Ti(IV) and Zr(IV)complex exhibit nanostructures. It is
clear from the antimicrobial data that complexes are slightly
more active than the parent ligands.
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The authors are thankful to the Head, Sophisticated Analyti-
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SEM, and elemental analysis data.
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