Synthesis, characterization and antibacterial screening activity of dibutyltin(IV) and triphenyltin(IV) complexes derivatives of 2,4-dinitrobenzoic and 3,5-dinitrobenzoic acids

Article abstract of DOI:10.14233/ajchem.2013.15086

In this work, five organotin(IV) carboxylate derivatives of 2,4-dinitrobenzoic and 3,5-dinitrobenzoic acids have been successfully synthesized and characterized quantitatively and qualitatively. Results of the spectroscopy studies indicated that the coord

Full text of DOI:10.14233/ajchem.2013.15086

Asian Journal of Chemistry; Vol. 25, No. 16 (2013), 9164-9168
http://dx.doi.org/10.14233/ajchem.2013.15086
Synthesis, Characterization and Antibacterial Screening Activity of Dibutyltin(IV) and
Triphenyltin(IV) Complexes Derivatives of 2,4-Dinitrobenzoic and 3,5-Dinitrobenzoic Acids
3
YIP-FOO WIN1,2,*, SIANG-GUAN TEOH2,* and EMAD YOUSIF
1Department of Chemical Science, Faculty of Science, Universiti TunkuAbdul Rahman, Perak Campus, Jalan Universiti, Bandar Barat, 31900
Kampar, Perak, Malaysia
2School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden Penang, Pulau Pinang, Malaysia
3Department of Chemistry, College of Science, Al-Nahrain University, Baghdad, Iraq
*Corresponding authors: Fax +605 4661676; Tel: +605 4688888; E-mail: williamyfw@yahoo.com
(Received: 4 January 2013;
Accepted: 18 September 2013)
AJC-14137
In this work, five organotin(IV) carboxylate derivatives of 2,4-dinitrobenzoic and 3,5-dinitrobenzoic acids have been successfully synthesized
and characterized quantitatively and qualitatively. Results of the spectroscopy studies indicated that the coordination took place via
oxygen atoms from the carboxylate anions to the tin atom moieties. From the NMR study, toluene molecule was presented in complexes
3 and 4 which have been clarified and identified. From the preliminary in vitro antibacterial screening study, all the complexes showed
some moderate and selective activity against the tested bacterial strains.
Key Words: 2,4-Dinitrobenzoic acid, 3,5-Dinitrobenzoic acid, Antibacterial activity, Organotin(IV) carboxylate.
tometer as KBr disc in the frequency range of 4000-400 cm-1.
INTRODUCTION
The H, H-13C HMQC and 119Sn NMR were recorded on a
Bruker AC-P 400MHz FTNMR Spectrometer and 13C NMR
was recorded on a Bruker AC-P 300MHz FTNMR Spectro-
meter using deuterated CDCl3 and DMSO-d6 as the solvent
and tetramethylsilane (TMS) as the internal standard. Elemen-
tal C, H and N analyses were carried out on a Fison EA 1108
CHNS-O analyzer. Tin was determined gravimetrically by
igniting a known quantity of each complex to SnO2. The
melting points were determined in an open capillary and were
uncorrected.
1
1
Nowadays, the synthesis, characterization and structural
study of organotin(IV) complexes have been well-known,
established and documented since the first organotin(IV)
compound was successfully isolated in 1850s1-7. The interest
and application of organotin(IV) carboxylate complexes have
also received considerable attention as these complexes display
a large array of applications in industries as catalysts, anti-
fouling agents, wood preservatives, crop protection agents,
etc.1. Up-to-date, organotin(IV) carboxylate complexes are
extensively studied due to the structural diversity (monomer,
dimeric, hexameric and oligomeric) and its biological pro-
Preliminary in vitro antibacterial screening activity:
The synthesized complexes and acids were screened for their
in vitro antibacterial activity against three gram-negative
(Escherichia coli, Pseudomonas aeruginosa and Klebsiella
pneumoniae) and two gram-positive (Bacillus subtilis and
Staphylococcus aureus) bacterial strains, by inhibition zone
method using agar well diffusion method. The seeded agar
(nutrient agar medium) was prepared by cooling the molten
agar to 40 ºC and then adding bacterial inoculums containing
approximately 104-106 colony forming units (CFU)/mL. The
bacterial inoculums were spread on the plate containing agar
medium and even coverage was ensured before the agar
solidified. The complexes were dissolved in DMSO to prepare
1.0 mg/mL concentration. By using a sterile metallic borer,
the wells (6 mm in diameter) were dug and the standard drugs
perties1-15
.
As part of our interest and research on organotin(IV)
work, we have synthesized and characterized organotin(IV)
carboxylate complexes derivatives of 2,4-dinitrobenzoic acid,
2,4-(NO2)2C6H3COOH and 3,5-dinitrobenzoic acid, 3,4-
(NO2)2C6H3COOH. In addition, the preliminary in vitro anti-
bacterial screening activity of the complexes obtained are
carried out and the results are reported herein.
EXPERIMENTAL
All the reagents and solvents were purchased commer-
cially and used without any further purification. Infrared spectra
were recorded using a Perkin-Elmer FTIR GX Spectropho-

Vol. 25, No. 16 (2013)
Synthesis and Antibacterial Activity of Dibutyltin(IV) and Triphenyltin(IV) Complexes 9165
and complexes were introduced into the respective wells. The
plates were incubated immediately at 37 ºC for 20-24 h. The
activity was determined by measuring the diameter of the
inhibition zone (in mm).
rences from those of their respective acids. The ν(O-H) bands
which appeared in the range of 2884-2465 cm-1 for the
respective acids were absent from the infrared spectra of the
sodium salts and complexes 1-5. In addition, infrared spectra
of complexes 1-5 also revealed that the ν(COO)as was shifted
to a lower wavelength number compared to the parent acids.
These two distinct appearances indicating the deprotonation
and coordination of the carboxylate anions to the tin atom
moieties as discussed and reported7.
Preparation of sodium salts and complexes: The sodium
salts of the respective acids were obtained by heating under
reflux a 1:1 molar ratio mixture of sodium hydroxide, NaOH
(3 mmol) with the respective acids (3 mmol) in ethanol (50
mL) for 2 h. After a few days, white precipitate was obtained.
Complexes 1-5 were synthesized by heating under reflux an
equivalent molar ratio mixture of parent organotin(IV)
[dibutyltin(IV) oxide or triphenyltin(IV) hydroxide] with the
respective acids in appropriate solvents (50-60 mL) for few
hours. Then, the respective clear yellow transparent solutions
were isolated by filtration and kept in a bottle. After few days,
yellow crystals were collected and washed with a small quantity
of polar solvent.
The1H NMR spectral data of complexes 1-5 are summa-
rized in Table-3, the 1H NMR spectra of complex 3 is depicted
in Fig. 2 as a representative; the 13C and 119Sn NMR spectral
data of complexes 1-5 are given in Table-4. In general, all the
aliphatic groups are located in the upfield regions whereas the
aromatic groups could be found in the downfield regions in
1
the NMR spectra. Based on the H and 13C NMR study, the
only exceptional case was the occurrence of toluene molecule
in complexes 3 and 4 which have been clarified and identified
in our previous report7. From the 119Sn NMR study, the tin
atom in complex 3 was five-coordinated as the chemical shifts
δ(119Sn) = -127.78 ppm fall in the range between -90 to -190
ppm which was assigned for five-coordinated tin atom16.
Complexes 1 and 4 were organodistannoxane dimer types and
exhibited two well resolved δ(119Sn) signals as usually expected
(1 = -190.69, -193.80 ppm and complex 4 = -194.27, -203.44
ppm)16. From the 119Sn NMR study, all the tin atoms in comp-
lexes 1, 3 and 4 were five-coordinated and exhibited distorted
trigonal bipyramid geometry. The chemical shifts δ(119Sn) of
triphenyltin(IV) carboxylate complexes showed a distinct diffe-
RESULTS AND DISCUSSION
Complexes 1-5 have been obtained in solid state and gave
a sharp melting point indicating that the isolation of fairly
pure complexes and the micro-elemental analysis for C, H, N
and Sn data obtained were in agreement with the predicted
formula. The micro-elemental and melting point of complexes
1-5 are given in Table-1 and an outline of the proposed reac-
tions and structure for complexes 1-5 are depicted in Fig. 1.
For better clarity, all the crystal structure data of complexes
1-5 (except complex 4) have been reported by our research
group9-12
.
The characteristic infrared absorption frequencies (cm-1)
and assignments for important absorption bands of the acids,
sodium salts and complexes 1-5 are listed in Table-2. The
infrared spectra of complexes 1-5 revealed the distinct diffe-
rent from the diorganotin(IV) carboxylate complexes17,18
.
Holecek et al.17,18 has proposed that for four-coordinated
triphenyltin(IV) carboxylate complexes, the chemical shifts
δ(119Sn) lie between -40 to -120 ppm. In this study, complexes
TABLE-1
MELTING POINT AND MICRO-ELEMENTAL ANALYSIS DATA OF COMPLEXES 1-5
Elemental (%)
Yield
(%)
m.p. (ºC)
Complexes
C
H
N
Sn
87.2
82.3
81.0
90.0
79.3
197.8-198.6
160.4-161.2
197.1-198.6
210.3-210.9
174.4-175.2
40.11 (39.86)
53.31 (53.51)
45.90 (46.61)
43.63 (44.61)
53.48 (53.51)
4.86 (4.68)
3.00 (3.23)
4.42 (4.32)
4.53 (5.06)
2.85 (3.23)
6.23 (6.20)
4.91 (5.00)
7.48 (7.50)
5.61 (5.62)
4.95 (5.00)
26.12 (26.26)
21.03 (21.15)
15.73 (15.88)
23.25 (23.83)
21.08 (21.15)
[{2,4-(NO2)2C6H3COO(C4H9)2Sn}2O]2 1
2,4-(NO2)2C6H3COO(C6H5)3Sn 2
{3,5-(NO2)2C6H3COO}2(C4H9)2Sn.C7H8 3
[{3,5-(NO2)2C6H3COO(C4H9)2Sn}2O]2.(C7H8)2 4
3,5-(NO2)2C6H3COO(C6H5)3Sn 5
Calculated values are given in parenthesis.
TABLE-2
SELECTED INFRARED DATA OF ACIDS, SODIUM SALTS AND COMPLEXES 1-5
Wavelength (cm-1)
Compounds
ν(OH)
ν(COO)as
1723
ν(COO)s
1346
∆ν
377
ν (Sn-O)
ν(Sn-O-Sn)/ν(O-Sn-O)
2,4-(NO2)2C6H3COOH
2882-2535
–
–
–
2,4-(NO2)2C6H3COONa
–
1569
1342
227
–
–
1659, 1539
1599
1346, 1376
1345
313, 163
254
475
453
–
636
–
1
–
2
3,5-(NO2)2C6H3COOH
2884-2465
1701
1348
358
–
3,5-(NO2)2C6H3COONa
–
–
–
–
1624
1346
278
–
–
1629
1345
284
467
477
444
684
632
–
3
4
5
1633, 1550
1655
1342, 1400
1343
291, 150
312
2,4-(NO2)2C6H3COONa = sodium salt of 2,4-dinitrobenzoic acid; 3,5-(NO2)2C6H3COONa = sodium salt of 3,5-dinitrobenzoic acid; ∆ν = [ν(COO)as-
ν(COO)s].

9166 Win et al.
Asian J. Chem.
Bu
Bu
NO
O N
2
2
Sn
C
NO
O N
2
C
O
O
O
2
O
O
O
O
Bu
Bu
Bu
Bu
Sn
Sn
NO
2
+ 2H2O
+
HOOC
4
Bu2SnO
4
O N
2
O
C
O
C
NO
Sn
O
2
O N
2
O N
2
NO
Bu
2
Bu
1
Ph
O
Ph3SnOH
+
HOOC
NO
2
Ph Sn
Ph
NO
C
+ H2O
2
O
O N
2
O N
2
2
NO
NO
NO
O N
2
Bu
Sn
2
2
2
O
O
toluene
+ H2O
C
C
HOOC
Bu2SnO
+
2
O
Bu O
H C
NO
O N
2
2
3
3
CH
3
Bu
Bu
NO
2
2
O N
2
Sn
C
C
O
O
O
NO
NO
2
2
O
O N
2
O
Bu
Bu
toluene
Bu
Bu
Sn
Sn
HOOC
+ 2H2O
4
Bu2SnO +
4
O
NO
O
C
NO
2
O
C
O N
2
Sn
O
O
NO
2
O N
2
Bu
Bu
H C
3
4
NO
NO
NO
2
2
2
Ph
O
O
Ph Sn
Ph
Ph3SnOH
+
HOOC
C
+ H2O
NO
2
5
Bu = butyl, Ph = phenyl
Fig. 1. Proposed reactions and structure for complexes 1-5
2 and 5 exhibited the δ(119Sn) values at -81.04 and -85.02 ppm,
respectively indicating that the tin atoms were four-coordinated
and have a distorted tetrahedral geometry.
larger than 10 mm but less than 16 mm are considered as
moderate and finally larger than 16 mm and above are active19,20
.
Between complexes 1 and 2 which were both derivatives of
2,4-dinitrobenzoic acid, complex 2 was found to be inactive
against Klebsiella pneumoniae and Pseudomonas aeruginosa
bacterial strains. However, the antibacterial activity of
The preliminary in vitro antibacterial screening activity
of acids and complexes 1-5 are given in Table-5. Inhibition
zones with a diameter less than 10 mm are considered as weak;

Vol. 25, No. 16 (2013)
Compounds
Synthesis and Antibacterial Activity of Dibutyltin(IV) and Triphenyltin(IV) Complexes 9167
TABLE-3
1H NMR DATA OF ACIDS AND COMPLEXES 1-5
Chemical shift, δ (ppm)
Benzene
Sn-R (R= Bu and Ph)
–
Toluene
–
8.09 (d, 8.5 Hz, 1H) H6
8.57 (dd, 2.2 Hz, 8.4 Hz, 1H) H5
8.76 (d, 2.2 Hz, 1H) H3
2,4-(NO2)2C6H3COOH
(d6-DMSO)
0.90 (t, 7.3 Hz, 12H) Hd
0.95 (t, 7.4 Hz, 12H) Hd
7.85 (d, 7.7 Hz, 4H) H6
8.56 (d, 6.9 Hz, 4H) H5
8.75 (s, 4H) H3
1 (CDCl3)
2 (CDCl3)
–
1.32-1.51 *(m, 32H) Hb and Hc
1.67-1.85 *(m, 16H) Ha
7.91(d, 8.4 Hz, 1H) H6
8.36 (dd, 2.2 Hz, 8.4 Hz, 1H) H5
8.60 (d, 2.1 Hz, 1H) H3
7.47-7.50 *(m, 9H) Hm and Hp
7.75-7.78 *(m, 6H) Ho
–
–
8.85 (d, 2.3 Hz, 2H) H2 and H6
8.99 (t, 2.2 Hz, 1H) H4
3,5-(NO2)2C6H3COOH (d6-
DMSO)
–
0.97 (t, 7.5 Hz, 6H) Hd
1.50 (sx, 7.3 Hz, 4H) Hc
1.82 (qn, 7.4 Hz, 4H) Hb
1.99 (t, 8.2 Hz, 4H) Ha
CH3; 2.36 (s, 3H)
CH2; 7.13-7.17 *(m, 3H)
CH2; 7.23-7.27 *(m, 2H)
9.27 (t, 2.2 Hz, 2H) H4
9.29 (d, 2.1 Hz, 4H) H2 and H6
3 (CDCl3)
0.83 (t, 7.1 Hz, 12H) Hd
0.96 (t, 6.2 Hz, 12H) Hd
1.36-1.48 *(m, 16H) Hc
1.81-2.03 *(m, 32H) Ha and Hb
7.49-7.55 *(m, 9H) Hm and Hp
7.79-7.83 *(m, 6H) Ho
CH3; 2.37 (6H, s)
CH2; 7.14-7.19 *(m, 6H)
CH2; 7.24-7.31 *(m, 4H)
4 (CDCl3)
5 (CDCl3)
9.20 (s, 12H) H2, H4 and H6
9.16 (t, 2.2 Hz, 1H) H4
9.21 (d, 2.1 Hz, 2H) H2 and H6
–
s = singlet, d = doublet, t = triplet, qn = quintet, sx = sextet, dd = doublet of doublet, m = multiplet; o = ortho, m = meta, p = para. Coupling
NO2
m
o
6
5
6
c
Sn CH3-CH2-CH2-CH2-Sn
5
b
a
d
i
1
1
4
p
4
NO2
HOOC
HOOC
3
2
3
2
NO2
O2N
constant = Hz, * = overlap.
.
TABLE-4
119Sn AND 13C NMR DATA OF ACIDS AND COMPLEXES 1-5
Chemical shift (ppm)
Compounds
Sn-R (R= Bu and Ph)
Benzene
119Sn
Toluene
–
COO
nJ(119Sn-13C) (n=1, 2, 3 and 4)
120.25 (C3), 128.66 (C1),
132.25 (C5), 133.52 (C6),
148.75 (C2), 149.56 (C4)
119.47 (C3), 127.21 (C1),
130.59 (C5), 135.62 (C6),
148.04 (C2), 148.44 (C4)
2,4-(NO2)2C6H3COOH
(d6-DMSO)
–
–
165.56
13.56 (Cd), 13.60 (Cd),
26.73 (Cc), 26.96 (Cc), 27.38 (Cb),
27.52 (Cb), 28.47 (Ca), 29.63 (Ca)
137.68 (1J = 655.6 Hz) (Ci),
137.27 (2J = 48.9 Hz) (Co),
129.66 (3J = 65.1 Hz) (Cm),
131.17 (4J = 13.1 Hz) (Cp)
-190.69
-193.80
168.56
169.67
–
1 (CDCl3)
2 (CDCl3)
119.58 (C3), 127.26 (C1),
132.21 (C5), 134.58 (C6),
148.73 (C2), 148.97 (C4)
-81.04
–
–
168.56
3,5-(NO2)2C6H3COOH
(d6-DMSO)
122.82 (C4), 129.66 (C2 and C6),
135.01 (C1), 149.16 (C3 and C5)
–
–
164.68
171.47
21.82
125.66, 128.59,
129.39, 138.23
122.92 (C4), 130.55 (C2 and C6),
134.78 (C1), 149.09 (C3 and C5)
13.87 (Cd)
26.17 (Cc), 26.83 (Cb), 27.10 (Ca)
-127.78
3 (CDCl3)
4 (CDCl3)
13.87 (Cd), 13.96 (Cd)
27.15 (Cc), 27.79 (Cc), 27.99 (Cb)
28.28 (Cb), 29.85 (Ca), 31.11 (Ca)
137.40 (1J = 644.5 Hz) (Ci),
137.30 (2J = 48.9 Hz) (Co),
130.68 (3J = 64.8 Hz) (Cm),
131.26 (4J = 13.1 Hz) (Cp)
21.76
125.65, 128.57,
129.38, 138.21
-194.27 122.20 (C4), 129.96 (C2 and C6),
-203.44 137.22 (C1), 149.13 (C3 and C5)
168.82
168.10
122.27 (C4), 129.68 (C2 and C6),
-85.02
5 (CDCl3)
–
135.73 (C1), 148.86 (C3 and C5)
NO2
5
m
o
6
5
3
6
2
c
CH3-CH2-CH2-CH2-Sn
b
a
d
i
1
1
4
p
Sn
4
NO2
HOOC
HOOC
3
2
NO2
O2N
.
triphenyltin(IV) (complex 2) was found to be more active
compared to the dibutyltin(IV) (complex 1) based on the
screening bioassays against Bacillus subtilis and Staphylococcus
aureus bacterial strains. In addition, in this series of study,

9168 Win et al.
Asian J. Chem.
TABLE-5
PRELIMINARY IN VITRO ANTIBACTERIAL SCREENING ACTIVITY OF ACIDS AND COMPLEXES 1-5
Inhibition zone (mm)
Complexes
Klebsiella
pneumoniae
Pseudomonas
aeruginosa
Staphylococcus
aureus.
Bacillus subtilis
Escherichia coli
2,4-(NO2)2C6H3COOH
15
13
16
17
15
11
13
29
34
25
11
12
9
12
10
-
17
9
19
12
19
21
14
24
10
30
28
37
1
-
2
3,5-(NO2)2C6H3COOH
11
13
11
10
-
10
11
10
8
14
11
9
3
4
-
5
*Chloramphenicol
*Doxycycline
*Rifampicin
23
21
23
34
40
29
24
24
Agar well diffusion method (in vitro) = 1.0 mg/mL; * = Reference drug.
there were some reversed results; complex 1 was found to
have more active compared to complex 2 based on the inhibition
zone diameter obtained upon screening against Escherichia
coli. This phenomenon was also detected in the in vitro anti-
bacterial studies of complexes 3-5 against the tested bacterial
strains. This contradicts with the fact that the increase in the
number of organo groups enhances the biological activity of
organotin(IV) complexes21,22. This phenomenon indicated that
the ligands (carboxylate anions) may play an important role
REFERENCES
1. S.J. Blunden, P.A. Cusack and R. Hill, The Industrial Uses of Chemicals,
Whitstable Litho Ltd., Great Britian (1985).
2. M. Gielen, M. Biesemans, D.D. Vos and R. Willem, J. Inorg. Biochem.,
79, 139 (2000).
3. S. Mahmood, S. Ali, M.H. Bhatti, M. Mazhar, R. Iqbal, K.M. Khan
and G.M. Maharvi, Turk. J. Chem., 27, 656 (2003).
4. S. Mahmood, S. Ali, M.H. Bhatti, M. Mazhar, K. Shahid, K.M. Khan
and G.M. Maharvi, Turk. J. Chem., 28, 17 (2004).
5. M.N. Xanthopoulou, S.K. Hadjikakou, N. Hadjiliadis, E. Milaeva, J.A.
Gracheva, V.Y. Tyurin, N. Kourkoumelis, K.C. Christoforidis, A.K.
Metsios, S. Karkabounas and K. Charalabopoulos. Eur. J. Med. Chem.,
43, 327 (2008).
in vitro antibacterial activity22-25
.
6. M. Hanif, M. Hussain, S. Ali, M.H. Bhatti, M.S. Ahmed, B. Mirza and
H. Stockli-Evans, Polyhedron, 29, 613 (2010).
CH3
H2C
7. Y.-F. Win, S.-G. Teoh, S.-T. Ha and T.-S. Tengku-Muhammad Afr. J.
Biotechnol., 11, 13140 (2012).
CH2
O3N
NO2
H2C
5
6
2
8. R. Zhang, J. Sun and C. Ma, J. Organomet. Chem., 690, 4366 (2005).
9. Y.F. Win, S.G. Teoh, N.L. Ismail and B.M. Yamin, Acta Cryst., E62,
m3146 (2006).
O
O
O
C
Sn
C
4
1
O
3
a
CH2
b
10. Y.F. Win, S.G. Teoh, J.B.J. Teh, H.K. Fun and L. Zakaria, Acta Cryst.,
E63, m323 (2007).
O2N
NO2
H C
2
c
CH2
11. Y.-F. Win, S.-G. Teoh, S.-T. Ha, T.-S. Tengku-Muhammad and E.Yousif,
Asian J. Chem., 25, 3376 (2013).
H3C
d
12. Y.F. Win, S.G. Teoh, E.K. Lim, S.L. Ng and H.K. Fun, J. Chem.
Crystallogr., 38, 345 (2008).
13. Y.F. Win, C.-S. Choong, S.-T. Ha, C.K. Quah and H.-K. Fun, Acta
Cryst., E67, m535 (2011).
14. Y.F. Win, C.-S. Choong, S.-G. Teoh, C.K. Quah and H.-K. Fun, Acta
Cryst., E67, m1276 (2011).
15. M. Danish, M.N. Tahir, S. Ghafoor, N. Ahmad, S. Ali and E.R.T.
Tiekink, J. Chem. Crystallogr., 41, 1365.
16. J. Holecek, M. Nadvorník, K. Handlír and A. Lycka, J. Organomet.
Chem., 315, 299 (1983).
Fig. 2. 1H NMR spectrum of complex 3
17. J. Holecek, K. Handlír, M. Nádvornik and A. Lycka, J. Organomet.
Chem., 258, 147 (1983).
Conclusion
18. J. Holecek, M. Nadvorník, K. Handlír and A. Lycka, J. Organomet.
Chem., 241, 177 (1983).
Complexes 1-5 have been successfully synthesized and
characterized quantitatively and qualitatively. Based on the
preliminary in vitro antibacterial screening activity, all the comp-
lexes obtained showed some moderate and selective activity
against the tested bacterial strains.
19. Y.-F. Win, S.-G. Teoh, M.R. Vikneswaran, S.-T. Ha and I. Pazilah, Int.
J. Phys. Sci., 5, 1263 (2010).
20 Z.H. Chohan, M.Arif, M.M. Akhtar and C.T. Supuran, Bioinorg. Chem.
Appl., 1 (2006).
21. S.-U. Rehman, S. Ali, M. Mazhar, A. Badshah and M. Parvez, Hetero-
atom Chem., 17, 420 (2006).
22. S.-U. Rehman, K. Shahid, S. Ali, M.H. Bhatti and M.Parvez. J.
Organomet. Chem., 690, 1396 (2005).
ACKNOWLEDGEMENTS
23. S.-U. Rehman, K. Shahid, S. Ali, M. Mazhar, A. Badshah, G. Eng, X. Song
and J. Ryczkowski, Heteroatom. Chem., 16, 175 (2005).
24. M. Nath, R. Yadar, G. Eng, T.-T. Nguyen and A. Kumar, J. Organomet.
Chem., 577, 1 (1999).
The authors would like to thank Universiti Tunku Abdul
Rahman (UTAR) and Universiti Sains Malaysia (USM) for
financial support as well as technical assistance and facilities.
25. M. Nath, R. Jairath, G. Eng, X. Song and A. Kumar, Spectrochim. Acta A,
62, 1179 (2005).