Synthesis and characterization of transition metal complexes with benzimidazolyl-2-hydrazones of o-anisaldehyde and furfural

Article abstract of DOI:10.5012/jkcs.2011.55.6.926

A series of complexes of the type [ML₂Cl₂], where L=2-(o-anisylidene-2′-imino) amino benzimidazole (AIAB) and 2-(furfurylidene imino) amino benzimidazole (FIAB), M=Cu(II), Co(II), Ni(II) and Zn(II), have been synthesized and characte

Full text of DOI:10.5012/jkcs.2011.55.6.926

Journal of the Korean Chemical Society
2011, Vol. 55, No. 6
Printed in the Republic of Korea
http://dx.doi.org/10.5012/jkcs.2011.55.6.926
Synthesis and Characterization of Transition Metal Complexes with
Benzimidazolyl-2-hydrazones of o-anisaldehyde and Furfural
R. K. Mohapatra*, U. K. Mishra†, S. K. Mishra†, A. Mahapatra†, and D. C. Dash†
Department of Chemistry, Orissa School of Mining Engineering (Degree Stream), Keonjhar-758002,
*
Orissa, India. E-mail: ranjank_mohapatra@yahoo.com
†School of Chemistry, Sambalpur University, Jyoti Vihar, Burla, Sambalpur-768019, Orissa, India
(Received July 13, 2011; Accepted November 4, 2011)
ABSTRACT: A series of complexes of the type [ML2Cl2], where L=2-(o-anisylidene-2’-imino) amino benzimidazole (AIAB)
and 2-(furfurylidene imino) amino benzimidazole (FIAB), M=Cu(II), Co(II), Ni(II) and Zn(II), have been synthesized and
characterized on the basis of elemental analysis, thermal analysis, molar conductivity, magnetic moment, electronic, infrared,
1H-NMR spectral studies. The results are in consistent with bidentate chelation of ligand with azomethine nitrogen and ring
nitrogen donors. All these Schiff bases and their complexes have also been screened for their antibacterial (Bacillus subtilis,
Bacillus stearothermophilus, Escherichia coli and Salmonella typhi) and antifungal activities (Aspergillus niger and Aspergil-
lus flavus).
Key words: Benzimidazolyl-2-hydrazones, o-anisaldehyde, Furfural and Transition metal complexes
amino benzimidazole (AIAB) and 2-(furfurylidene imino)
amino benzimidazole (FIAB).
INTRODUCTION
Schiff base complexes have undergone a phenomenal
growth during the recent years because of the versatility
offered by these complexes in the field of industries,1,2
catalysis3 and in biological system4,5 etc. In this way, the
synthesis, structural investigation and reaction of transi-
tion metal Schiff bases have received a special attention,
because of their biological activities as antitumoral, anti-
fungal and antiviral activities.6 Thus, Schiff base hydra-
zones are also interesting from the point of view of
pharmacology. Hydrazone derivatives are found to pos-
sess antimicrobial,7 antitubercular,8 anticonvulsant9 and
antiinflammatory10 activities. Particularly, the antibacte-
rial and antifungal properties of hydrazones and their
complexes with some transition metal ions was studied
and reported by Carcelli et al..11 In addition, complexes of
salicylaldehide benzoylhydrazone were shown to be a
potent inhibitor of DNA synthesis and cell growth.12 This
hydrazone also has mild bacteriostatic activity and a range
of analogues has been investigated as potential oral ion
chelating drugs for genetic disorders such as thalasemia.13,14
Following all these observations and as a part of our
continuing research on the coordination chemistry of mul-
tidentate ligands,15-22 we report here the synthesis and
structural studies on the complexes of Cu(II), Co(II), Ni(II)
and Zn(II) with some hydrazone derivatives containing
benzimidazole moiety such as 2-(o-anisylidene-2’-imino)
EXPERIMENTAL
Materials and Methods
All the chemicals used of AR grade. The solvents were
purified before use by standard procedures. The starting
material such as 2-hydrazinobenzimidazole was synthe-
sized according to literature method.23
Preparation of Ligands
The ligands used in the present investigation were ben-
zimidazolyl-2-hydrazones of aldehydes and ketones such
as o-anisaldehyde and furfural have been synthesized by
condensing 2-hydrazinobenzimidazole with respective
aldehydes and ketone in the following manner.
Ethanolic solution of 2-hydrazinobenzimidazole (0.01
mol in 20 mL) was added to ethanolic solution of o-anis-
aldehyde/furfural (0.01 mole in 20 mL), followed by
addition of 2 to 3 drops of piperidine as condensing
agent, to the above mixture. The resulting solution was
refluxed on a water bath for 3 hours. It was concentrated
and allowed to stand overnight when coloured precipi-
tate was separated out in each case. It was filtered,
washed and recrystallised from ethanol. The sample was
dried in vacuo over fused calcium chloride and then
analysed.
-926-

Synthesis and Characterization of Transition Metal Complexes with Benzimidazolyl-2-hydrazones of o-anisaldehyde and Furfural 927
Toshniwal conductivity Bridge (model CL-01-06, cell
constant 0.5 cm-1) using 1×10-3M solution of the com-
plexes in DMSO. Carbon, hydrogen and nitrogen con-
tents of the complexes were determined by using a MLW-
CHN micro analyser. FTIR spectra in KBr pallets were
Scheme 1.
recorded on a Varian FTIR spectrophotometer, Australia.
The electronic spectra of the complexes in DMSO were
recorded on a Perkin-Elmer spectrophotometer. Thermo
gravimetric analysis was done by Netzch-429 thermo ana-
lyzer. The 1H-NMR spectra of the complexes were recorded
in DMSO-d6 medium on JEOL, GSX-400 model equip-
ment.
Scheme 2.
Preparation of the complexes
A hot ethanolic solution of the ligand AIAB/FIAB (0.02
mole in 20 mL) was treated with ethanolic solution of
respective hydrated metal (II) chloride (0.01 mole in 20
mL) and the reaction mixture was refluxed on a water bath
with constant stirring for about 2-3 hours. The resulting
liquid was filtered and allowed to cool when coloured
crystals of the corresponding metal complexes separated
out in each case. The complexes were filtered, washed
with ethanol followed by ether and finally dried in vacuo
over fused CaCl2.
RESULTS AND DISCUSSION
The complexes were formulated from the analytical
data and molar conductance data support the suggested
formulae (Table 1). The complexes are highly coloured
and insoluble in water and common organic solvents but
soluble in highly coordinating solvents such as dioxane,
DMF and DMSO. They are non hygroscopic, highly sta-
ble under normal conditions and all of them decompose
above 250 oC. The molar conductance data values in
DMSO for the complexes indicate them to be non-elec-
trolyte in nature.
Analysis and Physical measurements: A weighed
quantity of the compound (0.2-0.3 g) was treated with a
few drops of concentrated H2SO4 and 1 cc. of concentrated
HNO3. It was heated till all the organic matter decom-
posed and sulphur trioxide fumes came out. The same pro-
cess was repeated two to three times to decompose the
substance completely. Then it was dissolved in water and
the resulting solution was used for analysis of metal ions.
The metal contents in the complexes were determined
gravimetrically following standard procedure.24 Sulphur
was determined as BaSO4. The molar conductance mea-
surements were carried out at room temperature with a
IR spectra
The IR spectra of the ligands AIAB and FIAB and their
metal complexes have been studied in concert for the
appraisal of the structure of the complexes. The formation
of the above ligands via the condensation of each of o-
anisaldehyde/furfural with 2-hydrazinobenzimidazole has
been confirmed by the disappearance of band due to νNH2
and appearance of a new band at ~1600 cm-1 which
undoubtedly originates due to newly introduced azome-
Table 1. Analytical and physical data of the ligands and their complexes
Yields
(%)
C Found
(Calcd)
H Found
(Calcd)
N Found
(Calcd)
Cl Found
(Calcd)
M Found
(Calcd)
Sl no
Compounds
Colours
Λam
1
2
AIAB
FIAB
Light yellow
Light brown
Silver grey
Royal ivory
80
83
65
62
-
-
40.78 (40.82) 5.23 (5.26) 44.41 (44.44)
41.23 (41.26) 4.38 (4.42) 40.06 (40.11)
-
-
-
-
3
Co(AIAB)2Cl2
Ni(AIAB)2Cl2
23.10 54.34 (54.38) 2.08 (2.11) 16.89 (16.92) 10.68 (10.72) 8.88 (8.91)
21.35 54.39 (54.41) 2.09 (2.11) 16.90 (16.93) 10.70 (10.73) 8.80 (8.84)
21.90 53.98 (54.01) 2.07 (2.10) 16.76 (16.80) 10.61 (10.65) 9.48 (9.53)
22.12 53.81 (53.86) 2.05 (2.09) 16.74 (16.76) 10.59 (10.62) 9.69 (9.73)
18.35 49.44 (49.48) 1.69 (1.72) 19.21 (19.24) 12.15 (12.19) 10.11 (10.13)
23.68 49.48 (49.51) 1.70 (1.72) 19.22 (19.25) 12.18 (12.20) 10.02 (10.06)
21.65 49.08 (49.10) 1.68 (1.71) 19.05 (19.09) 12.06 (12.10) 10.79 (10.82)
20.25 48.91 (48.95) 1.64 (1.70) 19.01 (19.04) 12.04 (12.07) 11.01 (11.05)
4
5
Cu(AIAB)2Cl2 Cannery yellow 63
6
Zn(AIAB)2Cl2
Co(FIAB)2Cl2
Ni(FIAB)2Cl2
Cu(FIAB)2Cl2
Zn(FIAB)2Cl2
White
Brown
64
60
61
63
60
7
8
Pale green
Steel grey
White
9
10
aOhm-1 cm2 mole-1
2011, Vol. 55, No. 6

928
R. K. Mohapatra, U. K. Mishra, S. K. Mishra, A. Mahapatra, and D. C. Dash
thine (C=N) group. The presence of furan ring in FIAB
and -OCH3 group in AIAB are also indicated by the
appearance of bands at ~1510 and ~2840 cm-1 in their
respective spectrum assignable to νC-O-C of furan ring and
-O-CH3 group of o-anisaldehyde respectively.25 The posi-
tion of above bands remain practically unaltered in the IR
spectra of complexes there by suggesting non participa-
tion of furan ring oxygen and methoxy oxygen atom in
coordination.
coordination of the counter ions Cl- to form neutral com-
plexes.
Thermal analysis
Thermal characteristics of the complexes formed by
AIAB and FIAB are recorded in Table 2. These com-
plexes follow the same pattern of thermal decomposition.
An examination of thermograms of the complexes reveals
that, the complexes remain almost stable up to ~235 oC
indicating absence of water molecules. Beyond this range,
the complexes decompose rapidly leaving their stable res-
idues. The rapid decomposition denotes loss of ligand
moiety. It has been observed that the composition of the
residue corresponds to the respective metal oxides. The
decomposition temperature varies for different com-
plexes. The representative thermogram of Cu(AIAB)2Cl2
complex is shown in Fig. 1. Thermal stability of the com-
plexes is found to be in the following order:
The characteristic IR bands observed in the spectra of
the ligands at ~1560, ~1303 cm-1 are assigned to νC=N (cyclic)
νC-N (cyclic) of benzimidazole group respectively. Anal-
ogous to the previous complexes, the position of both the
band remain unaltered suggesting there by nonparticipa-
tion of ring N atom (-C=N) in complexation. However,
νNH band of benzimidazole ring (-N-H) group was found
invariably shifted 20-10 cm-1 towards negative side indi-
cating the coordination of benzimidazole ring NH group
to the metal ions. Where as band occurring at ~3100 cm-1
due to νN-H exocyclic remains practically unaltered indi-
cating it’s non involvement either in coordination or eno-
lisation. Besides the above, the bands occurring at ~1600
and ~1010 cm-1 assignable to azomethine (νC=N) group
and (νN-N) respectively shifted their position on complex-
asation. Like previous cases here also, νC=N band under
goes red shift where as νCN band shows blue shift indi-
cating coordination of azomethine nitrogen atom to metal
ions. This is further confirmed by the presence of a band at
~525 cm-1 due to νNN. It is interesting to note that presence
of electron releasing group like -OCH3 and -C-O-C- near
the condensation site only enhance conjugation but do not
take part in coordination most probably due to steric hin-
drance.
AIAB Complexes: Co(II) < Zn(II) < Cu(II) < Ni(II)
FIAB Complexes: Co(II) < Ni(II) < Cu(II) < Zn(II)
Electronic spectra and magnetic properties
The electronic spectral data and room temperature
effective magnetic moment values of Co(II) complexes
Although evidence of νM-Cl band could not be brought in
the present investigation due to instrumental limitation,
the insolubility of the complexes in water and their non-
electrolytic nature provide sufficient evidence for the
Fig. 1. Thermogram of Cu(AIAB)2Cl2.
Table 2. Important features of thermo gravimetric analysis (TGA)
Sl.
no.
Total wt. of
TG (mg)
Decomposition
temperature (oC)
% weight of residue
Found (calcd.)
Composition of the
residue
Compounds
1
2
3
4
5
6
7
8
Co(AIAB)2Cl2
Ni(AIAB)2Cl2
Cu(AIAB)2Cl2
Zn(AIAB)2Cl2
Co(FIAB)2Cl2
Ni(FIAB)2Cl2
Cu(FIAB)2Cl2
Zn(FIAB)2Cl2
19.2
21.2
17.5
15.8
22.3
21.7
20.1
16.4
237-560
258-555
247-540
240-550
236-570
240-570
252-575
260-585
11.29 (11.33)
11.23 (11.26)
11.91 (11.93)
12.08 (12.12)
12.84 (12.88)
12.78 (12.81)
13.52 (13.55)
13.75 (13.77)
CoO
NiO
CuO
ZnO
CoO
NiO
CuO
ZnO
Journal of the Korean Chemical Society

Synthesis and Characterization of Transition Metal Complexes with Benzimidazolyl-2-hydrazones of o-anisaldehyde and Furfural 929
with the ligands AIAB and FIAB are recorded. The room
temperature µeff value of these complexes lies in the range
4.40-4.63 B.M. i.e., lower than expected for high spin
pesudo-octahedral Co(II) species.26 This lower µeff value
may be due to distorted structure of Co(II) complexes
under C2 symmetry. As in C2 symmetry the degeneracy of
the ground state of the metal ion will be lifted and the new
ground state being an orbital singlet state will give rise to
much lower magnetic moment than expected.27 Thus one
can infer that the present Co(II) complexes probably have
an orbital singlet ground state with distorted octahedral
environment, which is further evidenced by electronic
spectral data.
~14,000 cm-1 (714 nm) and ~26,000 cm-1 (386 nm). These
types of spectral features can be explained on the basis
of energy level schemes derived by Ballhausen and
coworkers30 for D4h symmetry. The first two bands cor-
respond to the split components of 3T2g (F) namely; 3B1g
→3Eg and 3B1g→3B2g while the third and fourth are due to
3
3B1g→3A2g and 3B1g→3Eg the split components of T1g (F)
term. The fifth one can be assigned to 3B1g (P)→3T1g (P)
transition. In this case the ground state term A2g under Oh
3
symmetry has been transformed to B2g term under D4h
symmetry.31
The electronic spectral data and room temperature µeff
values of Cu(II) complexes with ligands AIAB and FIAB
are recorded. The µeff value in theses cases lie in the range
1.82-1.88 B.M. as expected for hexa coordinated spin free
Cu(II) complexes in distorted octahedral environment. In
the electronic spectra of these complexes one broad enve-
lope is seen at ~16,000 cm-1 (625 nm). Suggesting super-
imposition of ν1, ν2 and ν3 transitions because of similar
The electronic spectra of these complexes show a broad
band at ~9000 cm-1 (1111 nm) and a split band at ~19,200-
20,500cm-1 (520-487 nm). The former band is attributed
to 4T1g(F)→4T2g(F) (ν1) and the later one is due to 4T1g(F)
→4T1g (P) (ν3) transitions respectively under Oh geome-
try. The broad asymmetrical curve seen as ν1 suggests the
presence of other bands which are superimposed by the ν1
band. It is possible to calculate the values of Dq and B
using band position of ν1 and ν3, following same method
as in previous cases. Value of ν2 has been calculated to be
around ~19000 cm-1 (526 nm). Thus, the observed weak
shoulder near ~19000 cm-1 may be tentatively assigned to
ν2 transition. From this it is concluded that the band
around ~16000-16,500 cm-1 is most likely due to spin for-
bidden 4T1g(F)→2T2g (G) transition and not due to 4T1g (F)
→4A2g (F) (ν2) transition.
2
energy. Thus above band corresponds to Eg→2T2g tran-
sition under a distorted octahedral environment. The
width of the band provides evidence for distortion. The
representative spectrum of the Ni(FIAB)2Cl2 complex is
shown in Fig. 2.
1H-NMR spectra
In the 1H NMR spectrum of the ligand AIAB, the mul-
tiplet is observed at δ 8.0-8.7 ppm correspond to 4 aro-
matic protons of benzimidazolyl group and 4 aromatic
protons -C6H4(OCH3) group. A signal observed at δ 7.0
ppm and δ 9.2 ppm correspond to ring NH proton of ben-
zimidazolyl group and exocyclic -NH-N= proton respec-
tively. Besides the above peaks, a sharp signal at δ 9.4
ppm and δ 4.7 ppm observed due to azomethine (-N=
CH-) protons and O-CH3 group respectively. In case of
AIAB complexes, the NH (cyclic) proton of benzimi-
dazolyl group show downfield shift indicating thereby
The spectral characteristics of Co(II) complexes with
AIAB and FIAB ligands with Cl- as co ligand do not indi-
cate pure octahedral or D4h symmetry, rather it suggests
approximately C2 geometry having distorted six coordi-
nate as supported by µeff values. This however requires
splitting of ν1 and ν3 bands due to lowering of symmetry.28
The electronic spectra has bands in the region ~19,200-
20,500 cm-1 which may be considered as the split com-
ponent of ν3 band and the shoulder near 19,000 cm-1 might
also contain one of the split Component of ν3 band. Although
no split Component of ν band is observed, yet the pres-
ence of a broad envelope suggests superimposition of the
different components into a single one.
The electronic spectral data and µeff value room tem-
perature for Ni(II) complexes with ligands AIAB and
FIAB with Cl- as co ligand have recorded. The observed
µeff values for these complexes advocate for a tetragonal
six-coordinated spin free Ni(II) species.29 The electronic
spectra of the complexes show a number of bands in the
range, ~8,600 cm-1 (1160 nm), ~10,400cm-1 (961nm),
Fig. 2. Electronic spectra of Ni(FIAB)2Cl2.
2011, Vol. 55, No. 6

930
R. K. Mohapatra, U. K. Mishra, S. K. Mishra, A. Mahapatra, and D. C. Dash
tative structure (Fig. 3) has been proposed for the present
complexes.
Antibacterial and antifungal activity
The Antibacterial activities of the synthesized com-
plexes were evaluated by the Agar Well Diffusion Assay
Technique against two Gram positive bacteria, i.e., Bacil-
lus subtilis and Bacillus stearothermophilus and two
Gram negative bacteria, i.e., Escherichia coli and Salmo-
nella typhi. Solutions of the ligands and its complexes in
DMF were plated onto the cultured agar medium and
incubated for a period of 24h at 37 oC. After the incuba-
tion period, the plates were observed for zones of inhi-
bition (in cm). The antifungal activities of the complexes
were determined against two fungal strains, i.e., A. niger
and A. flavus. The complexes showed good antibacte-
rial and antifungal activities (Table 3) against the spe-
cies. This may be explained on the basis that their
structures mainly possess C=N bonds. Moreover, coor-
dination reduces the polarity27,32 of the metal ion mainly
because of the partial sharing of its positive charge
within the chelate ring formed during coordination. This
process increases the lipophilic nature of the central
metal atom, which favors its permeation more effi-
ciently through the lipid layer of the micro-organism33-35
thus destroying them more aggressively. In addition to
this, many other factors, such as solubility, dipole
moment and conductivity, which are influenced by the
metal ion may be the possible reasons for the antibac-
terial activities of these metal complexes.36
Fig. 3. M = Co(II), Ni(II), Cu(II) and Zn(II).
the coordination of ring NH group to the metal ions,
while the azomethine proton show upfield shift in the
conformity with the coordination of azomethine group in
complexes.
In the 1H NMR spectrum of the ligand FIAB, the mul-
tiplet is observed at δ 8.0-8.7 ppm correspond to 4 aro-
matic protons of benzimidazolyl group and 3 additional
peaks at δ 5.4, δ 6.3 and δ 7.4 ppm corresponding to H-3,
H-4 and H-5 of (-C4H3O) ring. A signal observed at δ 7.0
ppm and δ 9.0 ppm correspond to ring NH proton of ben-
zimidazolyl group and exocyclic -NH-N= proton respec-
tively. Besides the above peaks, a sharp signal at δ 9.4
ppm is observed due to azomethine (-N=CH-) protons. In
case of FIAB complexes, the NH (cyclic) proton of ben-
zimidazolyl group show downfield shift indicating thereby
the coordination of ring NH group to the metal ions, while
the azomethine proton show upfield shift in the confor-
mity with the coordination of azomethine group in com-
plexes. It is to be noted that the multiplet due to aromatic
proton undergoes downfield shift to some extent probably
due to the involvement of ring NH group to the complex-
ation because of lowering electron density in the ring sys-
tem.
Based on the foregoing observations the following ten-
Table 3. Antibacterial and antifungal activities of the compounds (for a concentration of 100 µg mL-1)
Compound
AIAB
B. subtilis
17.38
16.76
41.53
22.39
19.91
20.42
28.23
21.85
25.83
22.48
B. stearothermophilus
E. coli
18.43
19.54
43.61
29.42
26.65
21.63
31.73
28.49
27.46
24.52
S. typhi
20.11
21.67
46.82
27.28
24.45
28.21
33.57
25.32
28.32
19.34
A. niger
12.53
7.84
A. flavus
11.49
9.28
15.63
13.39
36.64
25.78
21.45
19.37
19.87
26.27
22.19
18.67
FIAB
Co(AIAB)2Cl2
Ni(AIAB)2Cl2
Cu(AIAB)2Cl2
Zn(AIAB)2Cl2
Co(FIAB)2Cl2
Ni(FIAB)2Cl2
Cu(FIAB)2Cl2
Zn(FIAB)2Cl2
37.54
28.81
21.34
16.26
18.28
20.61
12.23
15.47
34.32
31.73
23.62
17.47
20.78
17.58
16.34
14.38
Journal of the Korean Chemical Society

Synthesis and Characterization of Transition Metal Complexes with Benzimidazolyl-2-hydrazones of o-anisaldehyde and Furfural 931
17. Dash, D. C.; Mahapatra, A.; Mohapatra, R. K.; Ghosh, S.;
Naik, P. Indian J. Chem. 2008, 47A, 1009.
18. Dash, D. C.; Mohapatra, R. K.; Ghosh, S.; Naik, P. J.
Korean Chem. Soc. 2008, 52(5), 468.
19. Dash, D. C.; Mohapatra, R. K.; Ghosh, S.; Naik, P. J.
Indian Chem. Soc. 2009, 86, 121.
20. Mohapatra, R. K. J. Indian Chem. Soc. 2010, 87, 1251.
21. Mohapatra, R. K.; Dash, D. C. J. Korean Chem. Soc.
2010, 54(4), 395.
22. Dash, D. C.; Mahapatra, A.; Naik, P.; Mohapatra, R. K.;
Naik, S. K. J. Korean Chem. Soc. 2011, 55(3), 412.
23. Katz, L. J. Am. Chem. Soc. 1951, 73, 4007.
24. Vogel, A. I. A text book of Quantitative Inorganic Anal-
ysis, 3rd ed.; Longman and ELBS: 1969.
Acknowledgement. The authors gratefully acknowl-
edge the services rendered by Director, Regional Sophis-
ticated Instrumentation Center, I.I.T., Madras, for recording
the spectra.
REFERENCES
1. Katsuki, T. Coord. Chem. Rev. 1995, 140, 189.
2. Di Bella, S. Chem. Soc. Rev. 2001, 30, 355.
3. Cogan, D. A.; Liu, G. C.; Kim, K. J.; Backes, B. J.; Ell-
man, J. A. J. Am. Chem. Soc. 1998, 120, 8011.
4. Pandeya, S. N.; Sriram, D.; Nath, G.; De Clercq, E. Eur.
J. Pharma. Soc. 1999, 9, 25.
5. Raper, E. S. Coord. Chem. Rev. 1996, 153, 199.
6. Sridhar, S. K.; Pandeya, S. N.; Stables, J. P.; Ramesh, A.
Eur. J. Pharm. Sci. 2002, 16, 129.
7. Vicini, P.; Zani, F.; Cozzini, P.; Doytchinova, I. Eur. J.
Med. Chem. 2002, 37, 553.
8. Kocyigit-Kaymakcioglu, B.; Rollas, S. Farmaco 2002, 57,
595.
9. Ragavendran, J. V.; Sriram, D.; Patel, S. K.; Reddy, I. V.;
Bharathwajan, N.; Stables, J.; Yogeeswari, P. Eur. J. Med.
Chem. 2007, 42, 146.
25. Kalsi, P. S. Spectroscopy of Organic Compounds, New
Age International limited; New Delhi, 1998; p 77.
26. Carlin, R. L. Transition Metal Chemistry; Marcel Dekker
Inc.: New York, 1965.
27. Lever, A. B. P. Inorganic Electronic Spectroscopy; Elsevier
Publication: New York, 1968.
28. Ali, M. A.; Livingstone, S. E. Coord. Chem. Rev. 1974,
13, 101.
29. Bustoup, O.; Jorgensen, C. K. Acta Chem. Scand. 1957,
11, 1223.
10. Rollas, S.; Gulerman, N.; Erdeniz, H. Farmaco 2002, 57,
171.
11. Carcelli, M.; Mazza, P.; Pelizi, C.; Zani, F. J. Inorg. Bio-
chem. 1995, 57, 43.
30. Sacconi, L. Trans. Metal Chem. 1968, 4, 199.
31. Ballhausen, C. J.; Liehr, A. D. J. Am. Chem. Soc. 1959,
81, 538.
32. Balhausen, C. J. An Introduction to Ligand Field; McGraw
Hill: New York, 1962.
33. Chohan, Z. H.; Pervez, H.; Kausar, S.; Supuran, C. T.
Synth. React. Inorg. Met.-Org. Chem. 2002, 3, 529.
34. Chohan, Z. H.; Pervez, H.; Rauf, A.; Supuran, C. T. Metal-
Based Drugs 2002, 8, 42.
35. Chohan, Z. H.; Scozzafava, A.; Supuran, C. T. J. Enzyme
Inhib. Med. Chem. 2003, 18, 259.
12. Johnson, D. K.; Murphy, T. B.; Rose, N. J.; Goodwin, W.
H.; Pickart, L. Inorg. Chim. Acta 1982, 67, 159.
13. Ranford, J. D.; Vittal, J. J.; Wang, Y. M. Inorg. Chem.
1998, 37, 1226.
14. Buss, J. L.; Greene, B. T.; Turner, J.; Torti, F. M.; Torti,
S. V. Curr. Top. Med. Chem. 2004, 4, 1623.
15. Dash, D. C.; Mahapatra, A.; Pathjoshi, S. B.; Mishra, U.
K.; Naik, S. K. J. Indian Chem. Soc. 2006, 83, 782.
16. Dash, D. C.; Mahapatra, A.; Jena, P.; Naik, S. K.; Mishra,
U. K. J. Indian Chem. Soc. 2007, 84, 1092.
36. Chohan, Z. H.; Hassan, M. U.; Khan, K. M.; Supuran, C.
T. J. Enzyme Inhib. Med. Chem. 2005, 20, 181.
2011, Vol. 55, No. 6