Coordination modes of a schiff base derived from substituted 2-aminothiazole with chromium(III), Manganese(II), Iron(II), Cobalt(II), Nickel(II) and Copper(II) Metal Ions: Synthesis, Spectroscopic and Antimicrobial Studies

Article abstract of DOI:10.1155/2011/282061

Transition metal complexes of Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) metal ions with general stoichiometry [ML2.2H2O] and [ML3], where M= Mn(II), Cr(III), Fe(II), Co(II), Ni(II) and Cu(II), L= Schiff base derived from the condensation of 2-ami

Full text of DOI:10.1155/2011/282061

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(4), 1750-1764
http://www.e-journals.net
Coordination Modes of a Schiff Base
Derived from Substituted 2-Aminothiazole with
Chromium(III), Manganese(II), Iron(II), Cobalt(II),
Nickel(II) and Copper(II) Metal Ions: Synthesis,
Spectroscopic and Antimicrobial Studies
AMBIT THAKAR*, KRISHNAKANT JOSHI§,
KISHOR PANDYA and ARVIND PANCHOLI§
*Zydus Research Centre, Ahmedabad-382 210, India
§Department of Chemistry
Navjivan Science College, Dahod-389 151, India
Sir P.T. Science College, Modasa-383 315, India
krishnakant_joshi@yahoo.co.in
Received 9 November 2010; Accepted 21 January 2010
Abstract: Transition metal complexes of Cr(III), Mn(II), Fe(II), Co(II), Ni(II)
and Cu(II) metal ions with general stoichiometry [ML2.2H2O] and [ML3],
where M= Mn(II), Cr(III), Fe(II), Co(II), Ni(II) and Cu(II), L= Schiff base
derived from the condensation of 2-amino-4(4’-phenyl/methylphenyl)-5-
methyl-thiazole with 4-acetyl-1(3-chloro phenyl)-3-methyl-2-pyrazoline-5-
ones, have been synthesized and structurally characterized by elemental
analysis, molar conductance measurements, magnetic susceptibility
1
measurements and spectral techniques like IR, UV, H NMR, 13C NMR and
Mass Spectra. All the complexes were found to be octahedral geometry. The
ligand and its complexes have been screened for their antifungal and
antibacterial activities against three fungi, i.e. Alternaria brassicae,
Aspergillus niger and Fesarium oxysporum and two bacteria, i.e. Xanthomonas
compestris and Pseudomonas aeruginosa.
Keywords: 2-Aminothiazole, Schiff base, Transition metals, Biological activities
Introduction
The thiazole ring is important in nature. It occurs, for example, in thiamine, a coenzyme
required for the oxidative decarboxylation of α-keto acids. A tetrahydrothiazole also appears

1751
AMBIT THAKAR et al.
in the skeleton of penicillin which is one of the first and still most important of the broad-
spectrum antibiotics. Thiazolamine are key intermediates for synthesizing many
pharmaceuticals1. Some thiazolidone are valuable medicines2. It is obvious that
compounds with the thiazole ring have potential biological activity. It is also known that
some Schiff bases are effective antitumor drugs and antibacterials. Aminothiazoles are
known to be ligands of the estrogen receptor and as a novel class of adenosine receptor
antagonists3. We were interested in examining the biological activities of NO-donnor
schiff’s bases and their transition metal complexes, thus, in this article, we report the
anti fungal and antibacterial activities of the Schiff base ligands 1-(3-chlorophenyl)-3-
methyl-4-(1-((5-methyl-4-phenylthiazol-2-yl)imino)ethyl)-1H-pyrazol-5-ol (L), 1-(3-
chlorophenyl)-3-methyl-4-(1-((5-methyl-4-(p-tolyl)thiazol-2-yl)imino)ethyl)-1H-pyrazol-
5-ol (L1) and Its complexes with Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) metal
ions. The ligand and its complexes were characterized by physiochemical and spectral
studies.
Experimental
All the chemicals used in the present study were of A.R. grade. 1,4-Dioxane and methanol
(SD’s fine chemical Ltd., Mumbai and Merck chemicals., Mumbai) were used without
further purification. Absolute ethanol from alembic chemical works Co. Ltd., Baroda was
used after distillation. Cr(III), Mn(II), Co(II), Ni(II), Cu(II) metal acetate and Fe(II) sulphate
(SD’s fine chemical Ltd, Qualigens-Glaxo, Mumbai and Merck chemicals., Mumbai) were
used.
Melting points were taken in one side open capillaries on a melting point apparatus
having model number VMP-D of a make VEEGO. The Mass spectra of all ligands were
recorded on the instrument named LCMS-2010A of make Shimadzu. Carbon, Hydrogen and
Nitrogen were estimated on a Thermo fisher (Thermo electron corporation Limited), Flash
Elemental Analyzer-1112. The 1H NMR and 13C NMR spectra of all the ligands [in
Deuterated Chloroform(CDCl3)] were recorded on a AVANCE-II 400 of make BRUKER
spectro-photometer using TMS [(CH3)4Si] as internal standard. The Infrared spectra of the
ligands studied in the present work were recorded on the model FT-IR-8300 of Shimadzu in
KBr (Zydus Research Center, Ahmedabad, India).
Synthesis of the Schiff base ligands
1-(3-Chlorophenyl)-3-methyl-4-(1-((5-methyl-4-phenylthiazol-2-yl)imino)ethyl)-1H-
pyrazol-5-ol (L)
A hot solution of 4-acetyl-3-methyl-1-(3’-chlorophenyl)-2-pyrazolin-5-one (0.1 mol, 25
g) in methanol (50 mL) was slowly added drop wise to a hot solution of 2-amino-4-
phenyl-5-methyl thiazole (0.1 mol, 19 g) in methanol (38 mL). The resulting solution
was refluxed for 7 h at 64˚C. The Solid compound precipitated out is filtered, washed
with cold methanol and dried under vacuum oven at 50˚C. Yield: 28.6 g (68%). m.p.=
191 ˚C. Anal. Calcd. For C22H19ClN4OS: C, 62.48; H, 4.53; N, 13.25; S, 7.58. Found: C,
61.80; H, 4.44; N, 13.04; S, 7.82.
1-(3-Chlorophenyl)-3-methyl-4-(1-((5-methyl-4-(p-tolyl)thiazol-2-yl)imino)ethyl)-
1H-pyrazol-5-ol (L1)
A hot solution of 4-acetyl-3-methyl-1-(3’-chlorophenyl)-2-pyrazolin-5-one (0.1 mol, 25 g)

Synthesis, Spectroscopic and Antimicrobial Studies
1752
in methanol (50 mL) was slowly added drop wise to a hot solution of 2-amino-4-(4’-
methylphenyl)-5-methyl thiazole (0.1 mol, 20.4 g) in methanol (40 mL). The resulting
solution was refluxed for 7 h at 64 ˚C. The Solid compound precipitated out is filtered,
washed with cold methanol and dried under vacuum oven at 50˚C. Yield: 30.48 g (70%).
M.P. = 178 ˚C. Anal. Calcd. For C22H19ClN4OS: C, 63.22; H, 4.84; N, 12.82; S, 7.34.
Found: C, 61.53; H, 4.69; N, 12.37; S, 7.47.
Synthesis of the metal complexes
To hot solution of Schiff base ligands (1 mmol) in dioxane (15 mL), a hot solution of
corresponding metal salt like nitrate, chloride, acetate or sulphate (1 mmol) in dioxane
(10 mL) was added slowly with constant stirring. The resulting mixture was refluxed
for 8 to 10 h at 85 to 90 ˚C. On cooling the mixture overnight at 0 ˚C, the colored
product which separated out was filtered, washed with dioxane and dried under
vacuum oven at 60 ˚C.
Results and Discussion
The synthesized novel Schiff base ligands, 1-(3-chlorophenyl)-3-methyl-4-(1-((5-methyl-
4-phenylthiazol-2-yl)imino)ethyl)-1H-pyrazol-5-ol (L) and 1-(3-chlorophenyl)-3-methyl-
4-(1-((5-methyl-4-(p-tolyl)thiazol-2-yl)imino)ethyl)-1H-pyra zol-5-ol (L1) (Scheme 1)
forms stable complexes with Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) metal ions.
The analytical data of complexes, together with physical properties are given in Table 1.
The analytical data of the complexes correspond to the general stoichiometry [ML2.2H2O]
and [ML3], where M= Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II), Ligand L=Schiff
base L and L1. The value of molar conductance (λM) of the complexes in DMSO indicates
that the [ML2.2H2O] and [ML3] are non-electrolytes4. Magnetic moments lie in the range
1.81-1.89 B.M., 5.72-5.76 B.M., 4.96-5.02 B.M., 4.42-4.48 B.M., 2.89-2.95 B.M and
1.90-1.94 B.M., for Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes
respectively.
Mass spectra
Mass spectra provide a vital clue for elucidation of compounds. The ESI mass spectrum of
ligand L and L1 are given below. The spectrum in Figure 1 shows the molecular ion peak at
m/z = 423.14 and the isotopic peak at m/z = 424.99 due to 35Cl and 37Cl isotopes of ligand L.
The spectrum in Figure 2 shows the molecular ion peak at m/z = 437.13 and the isotopic
peak at m/z = 439.18 due to 35Cl and 37Cl isotopes. In both the spectra the molecular ion
peak is base peak and the intensity of these peaks reflects the stability and abundance of the
ions5.
R
O
H3C
R
CH3
N
CH3
OH
N
H3C
H2N
N
CH3
N
S
N
Methanol
N
S
OH
N
Reflux
3hours
CH3
L : R= H
L1: R=CH3
R= H, CH3
Cl
Cl
2-Amino-4(4'-phenyl/methyl
phenyl)-5-methyl-thiazole
1-(1-(3-chlorophenyl)-5-hydroxy-3-
methyl-1H-pyrazol-4-yl)ethanone
Schiff base-ligand
Scheme 1. Synthesis of ligand

Table 1. Analytical data and physical properties of complexes
λM,
Elemental analysis data (%)
Found (Calculated)
M P,
˚C
Yield,
%
Complex
M W
Color
Ω-1cm-1
mol-1
C
61.80
H
4.44
N
13.04
S
7.82
M
Cl
8.11
(8.38)
8.13
Ligand-L C22H19ClN4OS
422.93 Brown
191
-
68
65
70
65
62
60
64
70
70
65
60
67
65
62
-
(62.48) (4.53) (13.25) (7.58)
59.82 3.97 12.87 7.36
3.94
Cr (L)3 C65H52Cl3CrN12O3S3
1303.7 Brown 256*
934.81 Creamy 239
11.94
12.12
10.25
12.21
9.32
(59.88) (4.02) (12.89) (7.38) (3.99) (8.16)
56.55 4.34 12.01 6.84 5.90 7.61
(56.53) (4.31) (11.99) (6.86) (5.88) (7.59)
56.50 4.33 11.94 6.87 5.99 7.59
(56.48) (4.31) (11.98) (6.85) (5.97) (7.58)
56.32 4.28 11.97 6.85 6.29 7.45
(56.29) (4.29) (11.94) (6.83) (6.28) (7.55)
56.34 4.32 11.92 6.87 6.24 7.59
(56.31) (4.30) (11.94) (6.83) (6.25) (7.55)
56.06 4.24 11.86 6.85 6.76 7.49
(56.02) (4.27) (11.88) (6.80) (6.74) (7.52)
Mn (L)2.2H2O
C44H40Cl2MnN8O4S2
Fe (L)2.2H2O C44H40Cl2FeN8O4S2 935.72 Brown 224*
Dark
Brown
Co (L)2.2H2O C44H40Cl2CoN8O4S2 938.81
263*
281*
210
Ni (L)2.2H2O C44H40Cl2N8NiO4S2 938.57 Green
Cu (L)2.2H2O C44H40Cl2CuN8O4S2 943.42 Brown
11.32
-
61.53
(63.22) (4.84) (12.82) (7.34)
60.72 4.36 12.47 7.12
4.69
12.37
7.47
8.08
(8.11)
8.01
Ligand-L1 C23H21ClN4OS
436.96 Brown
178
-
3.85
Cr (L1)3 C68H58Cl3CrN12O3S3
1345.8 Brown 266*
962.67 Creamy 222
8.88
(60.69) (4.34) (12.49) (7.15) (3.86) (7.90)
57.40 4.62 11.67 6.67 5.70 7.41
(57.38) (4.61) (11.64) (6.66) (5.71) (7.36)
57.36 4.62 11.60 6.67 5.77 7.32
(57.33) (4.60) (11.63) (6.64) (5.79) (7.36)
57.17 4.57 11.62 6.66 6.14 7.11
(57.14) (4.59) (11.59) (6.62) (6.10) (7.33)
57.19 4.62 11.57 6.66 6.04 7.29
(57.16) (4.59) (11.59) (6.63) (6.07) (7.34)
56.88 4.59 11.50 6.59 6.56 7.22
(56.87) (4.57) (11.53) (6.60) (6.54) (7.30)
Mn (L1)2.2H2O
C46H44Cl2MnN8O4S2
Fe (L1)2.2H2O
C46H44Cl2FeN8O4S2
Co (L1)2.2H2O
C46H44Cl2CoN8O4S2
10.34
9.32
963.77 Brown
231
252
276*
229
Dark
966.86
10.24
10.35
12.45
Brown
Ni (L1)2.2H2O C46H44Cl2N8NiO4S2 966.62 Green
Cu (L1)2.2H2O C46H44Cl2CuN8O4S2 971.47 Brown
*
decomposition temperature

Synthesis, Spectroscopic and Antimicrobial Studies
1754
Figure 1. Mass spectrum of the ligand L
Figure 2. Mass spectrum of the ligand L1
NMR spectra
NMR data of ligand L are given in Table 2. Its 1H NMR spectrum (Figure 3) displays three
singlets at ca. δ 2.43 -2.86 ppm (s, 9H, 3H3C-C) due to the nine protons of three methyl
groups, at ca. δ 7.12-8.08 ppm (m, 9H, aromatic) due to the protons of two phenyl rings and
a singlet at ca. δ 13.75 ppm (s, 1H, -OH) due to the alcohol and NMR data of ligand L1 are
1
given in Table 3. Its H NMR spectrum (Figure 4) displays four singlets at ca. δ 2.36 -2.86
ppm (s, 12H, 4H3C-C) due to the twelve protons of four methyl groups, at ca. δ 7.12-8.08
ppm (m, 9H, aromatic) due to the protons of two phenyl rings and a singlet at ca. δ 13.73
ppm (s, 1H, -OH) due to the alcohol6.

1755
AMBIT THAKAR et al.
Table 2. The NMR data of Schiff base ligand L
1H NMR 13C NMR
Assignment Assignment
2.43-2.86 s, 9H, 3H3C-C
δ, ppm
δ, ppm
12.72
17.87
18.31
102.96
Primary Carbon C(4)
Primary Carbon C(16)
Primary Carbon C(12)
C=C of Pyrazolone C(13)
7.12-8.08
13.75
m, 9H, Ar
s, 1H, -OH
9
8
10
2
116.94-128.55 Tertiary Aromatic Carbon
Quaternary Aromatic Carbon
129.91-134.63
7
12
5
6
16
C(5), C(19), C(17)
1
3
11
15
4
13
139.79
148.48
148.51
154.94
161.49
165.51
C=C of thiazole ring C(1)
C=N of Pyrazolone C(14)
C=C of thiazole ring C(2)
C-OH of Pyrazolone C(15)
C=N of Azomethine C(11)
C=N of thiazole ring C(3)
14
17
22
21
18
19
20
Table 3. The NMR data of Schiff base ligand L1
1H NMR
Assignment
13C NMR
δ, ppm
2.36-2.86
7.12-8.08
13.73
δ, ppm
12.73
17.88
18.31
21.40
102.91
Assignment
s, 12H, 3H3C-C
m, 8H, Ar
Primary Carbon C(4)
Primary Carbon C(17)
Primary Carbon C(13)
Primary Carbon C(11)
C=C of Pyrazolone C(14)
s, 1H, -OH
11
H3C
9
8
7
116.97-
129.26
Tertiary Aromatic Carbon
10
2
13
5
6
Quaternary Aromatic
Carbon C(5), C(8), C(20),
C(18)
129.91-
137.86
17
1
3
12
14
4
15
16
139.83
148.29
148.60
154.79
161.54
165.53
C=C of thiazole ring C(1)
C=N of Pyrazolone C(15)
C=C of thiazole ring C(2)
C-OH of Pyrazolone C(16)
C=N of Azomethine C(12)
C=N of thiazole ring C(3)
18
19
20
23
22
21
The 13C NMR spectrum of ligand L (Figure 5) displays the signals corresponding to the
different non-equivalent carbon atoms at different values of δ as follows: at ca. δ 12.72 ppm,
δ 17.87 ppm and δ 18.31 ppm (H3C-C) corresponding to carbon atoms of methyl groups; at
ca. δ 102.96 ppm (C=C) due to carbon atom of pyrazolone ring; at ca. δ 116.97-134.36 ppm
due to aromatic carbon atoms; at ca. δ 139.79 (C=C) due to carbon atom of thiazole ring; at
ca. δ 148.48 (C=N) due to carbon atom of pyrazolone ring; at ca. δ 148.51 (C=C) due to
carbon atom of thiazole ring; at ca. δ 154.94 (C-OH) due to carbon atom of pyrazolone ring;
at ca. δ 161.49 (C=N) due to carbon atom of azomethine and at ca. δ 165.51 (C=N) due to
carbon atom of thiazole ring. In the same manner 13C-NMR spectrum of ligand L1 (Figure 6)
describe in Table 3.

Synthesis, Spectroscopic and Antimicrobial Studies
1756
Figure 3. 1H NMR spectrum of the ligand L
Figure 4. 1H NMR spectrum of the ligand L1

1757
AMBIT THAKAR et al.
Figure 5. 13C NMR spectrum of the ligand L
Figure 6. 13C NMR spectrum of the ligand L1

Synthesis, Spectroscopic and Antimicrobial Studies
1758
IR spectra
Selected IR bands of the ligand and its complexes are listed in Table 4. The infrared spectra
of the both ligands L and L1 show υ
(weakly H-bonded) at 3345 cm-1 and 3320 cm-1
O-H
respectively7. The absence of this band in all the metal complexes indicates the removal of
proton of hydroxyl group of pyrazolin ring during the chelation. This is further supported by
the shift of C-O frequency from ~1315 cm-1 (in ligand) to the higher frequency 1330-1400 cm-1
(in complexes)8. The sharp intense band at 1626 cm-1 and 1627 cm-1 respectively in the
ligands can be assigned to υ C=N (azomethine). A downward shift (∆υ = 15-35 cm-1) in υ C=N
(azomethine) is observed upon coordination indicating that the nitrogen of azomethine group
is involved in coordination. All the complexes show broad band in the region 3250 cm-1 to
3500 cm-1 which may be assigned to υ
of coordinated water9. To account for the
O-H
octahedral stereochemistry of the metal complexes, the coordination of two water molecules
is expected.
Table 4. Selected IR bands of Schiff base ligand L, ligand L1 and its complexes
Ligand
Metal complexes of
Assignment
Ligand L
3345 (w,br)
-
Cr(III) Mn(II) Fe(II) Co(II) Ni(II) Cu(II)
-
-
-
-
-
-
-
υO-H (Enolic)
3431
1613
1589
1520
3371 3423 3404 3358 υO-H (Coordinated water)
1626 (s,s)
1587 (s,s)
1516 (s,s)
1604
1582
1535
1614 1600 1604 1591
1591 1583 1590 1586
1533 1535 1520 1520
υ
υ
υ
C=N (Azomethine)
C=N (Pyrazolin)
C=C (Phenyl ring)
1477 (s,s)
1452 (s,s)
1315 (s,s)
1265 (m,s)
1120 (m,br)
-
1487
1442
1383
-
1120
-
758
657
520
1485
1431
1381
-
1124
883
731
657
582
1492 1473 1490 1495 Thiazole ring stretching
1444 1411 1454 1467 Pyrazolin ring stretching
1383 1354 1346 1330
υ
δ
C-O (Enol)
O-H (Enol)
1128 1190 1120 1120 Pyrazolin ring breathing
-
-
-
-
819
756
653
510
871 801
756 729
623 682
518 530
846
709
640
590
υO-H (coordinated water)
C-Cl Stretch
υM-O
767 (m,br)
-
-
υM-N
Ligand L1
3320 (w,br)
-
Metal complexes
-
Assignment
-
-
-
-
-
-
υO-H (Enolic)
3396
1622
1582
1520
1504
1477
1357
-
1141
829
727
605
509
3346 3423 3443 3246 υO-H (Coordinated water)
1627 (s,s)
1589 (s,s)
1527 (s,s)
1498 (s,s)
1479 (s,s)
1310 (s,s)
1209 (m,s)
1178 (m,br)
-
1600
1583
1533
1494
1475
1323
-
1187
-
717
673
590
1609 1602 1606 1610
1585 1586 1585 1588
1532 1521 1520 1530
1501 1496 1483 1502
1479 1465 1442 1425
1332 1327 1354 1355
υ
υ
υ
C=N (Azomethine)
C=N (Pyrazolin)
C=C (Phenyl ring)
Thiazole ring stretching
Pyrazolin ring stretching
C-O (Enol)
δO-H (Enol)
Pyrazolin ring breathing
υO-H (coordinated water)
C-Cl Stretching
υM-O
υ
-
1101 1111 1176 1141
-
-
-
833
735
690
565
829 821 806
780 775 738
667 682 623
516 468 484
759 (m,br)
-
-
υM-N

1759
AMBIT THAKAR et al.
The bands in the range between 450 cm-1 to 590 cm-1 may be due to metal-nitrogen
stretching vibration10 of Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes. The
bands in the range between 600 cm-1 to 690 cm-1 may be due to metal-oxygen stretching
vibration11 of Cr(III), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes. A less intense
band between 1610 cm-1-1560 cm-1 in the spectrum of ligand may be assigned to υ
C=N
(pyrazolin ring)12. All the metal complexes do not show shifting in υ
respective ligands. This suggests that the nitrogen atom of the ring has not participated in the
compared to its
C=N
chelation. However, in water containing chelates, this band is observed as a broad. This may
13
be due to coupling of the bending mode of coordinated water molecules with υ C=N
.
Electronic spectra
The electronic spectra of the complexes were recorded in DMSO solution. Both the ligands
show two absorption bands (Figure 7) at 37313 cm-1, 26385 cm-1 and (Figure 8) 37453 cm-1,
26246 cm-1 respectively. No absorption was observed in the visible region for any of the
ligands. In the absence of Quantum mechanical calculation, it is not possible to assign the
absorption bands to definite electronic transitions with complete certainty. However, it
appears reasonable to assign the bands to π→ π* transitions.
Wavelength, nm
Figure 7. UV spectra of the ligand L
Wavelength, nm
Figure 8. UV spectra of the ligand L1
The electronic spectra of chromium(III) complexes display the d-d transition bands in
the region 23,000-15,900 cm-1 and 29,100-24,500 cm-1. This transitions may be assigned to
4
4
the A2g →4T2g (υ1) and A2g →4T1g (F) (υ2) and respectively. The transitions correspond to
the typical octahedral geometry of the complexes.

Synthesis, Spectroscopic and Antimicrobial Studies
1760
The electronic spectra of Manganese (II) complexes display the d-d transition bands in
the region 17,000-14,800 cm-1, 19,200-17,900 cm-1 and 26,300-25,300 cm-1. This transitions
may be assigned to the 6A1g →4T1g (G), 6A1g →4T2g(G) and 6A1g →4A1g, 4Eg,(G) respectively.
The transitions correspond to the octahedral geometry of the complexes14.
The electronic spectra of iron(II) complexes display the d-d transition broad bands in
the region 14,700-12,300 cm-1 and 27,300-25,100 cm-1. The latter high energy band might
be charge transfer in nature and low energy band may be assigned to the spin-allow
transition 5T2g →5Eg which correspond to the typical octahedral geometry of the complexes.
The electronic spectra of cobalt(II) complexes display the d-d transition bands in the
region 9,350-8,400 cm-1, 20,000-18,600 cm-1 and 28,100-26,500 cm-1. The first two bands
4
4
may be correspond to T1g(F) →4T2g(F) υ1 and T1g(F) →4T1g(P) υ3 transitions respectively.
These bands are the characteristics of high spin octahedral Co(II) complexes. However υ2
band is not observed because of its proximity to strong υ3 transitions.
The electronic spectra of nickel(II) complexes display the d-d transition bands in the
region 11,900-8,500 cm-1, 20,700-13,200 cm-1 and 26,200-19,500 cm-1. This transitions may
be assigned to the 3A2g→3T2g(F) υ1, 3A2g→3T1g(F) υ2 and 3A2g→3T1g(p) υ3 respectively. These
transitions reveal that the nickel complexes possess an octahedral geometry and D4h symmetry.
For the Cu(II) complexes with D4h symmetry, three spin allowed transitions 2B1g→2A1g
2
(υ1),2B1g→2B2g (υ2) and B1g→2Eg (υ3) are possible but the electronic spectra of Cu(II)
complexes display two bands at 14,367 cm-1, 21,448 cm-1 and 14,198 cm-1, 21,290 cm-1
respectively. There should be third transition but we could not observe the same which may
be due to very close energy values of different states. Absence of any spectral band below
10000 cm-1 rule out the possibility for tetrahedral structure of the present complexes are also
suggestive for distorted octahedral geometry of the complexes.
Thermogravimetric analysis
Thermogravimetric analysis of Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes
The thermograms of this group of metal complexes show three stages decomposition (Table 5).
All the metal complexes do not show weight loss below 120 °C, it indicates the absence of
lattice water in the metal complexes.
Table 5. Thermo analytical results of metal complexes of Schiff base ligand L and ligand L1
Stage-I [140-210 °C]
Mass lose
Stage-II [210-400 °C]
Mass lose
Obs. (Calc.)
Stage-III [400-900 °C]
Mass lose
Obs. (Calc.)
Compounds
Obs. (Calc.)
3.81 (3.85)
3.82 (3.85)
[Mn(L)2.2H2O]
[Fe(L)2.2H2O]
[Co(L)2.2H2O]
[Ni(L)2.2H2O]
[Cu(L)2.2H2O]
[Mn(L1)2.2H2O]
[Fe(L1)2.2H2O]
[Co(L1)2.2H2O]
[Ni(L1)2.2H2O]
[Cu(L1)2.2H2O]
87.67 (87.92)
87.58 (87.83)
8.12 (8.20)
8.47 (8.53)
3.80 (3.84)
3.81 (3.83)
3.86 (3.81)
3.69 (3.74)
3.78 (3.74)
3.70 (3.72)
3.64 (3.72)
3.66 (3.70)
Loss of two
coordinated water
molecules
88.41 (88.49)
90.19 (90.12)
88.04 (87.96)
88.16 (88.27)
88.14 (88.19)
88.64 (88.73)
90.32 (90.41)
90.79 (90.94)
7.84 (7.99)
6.20 (6.25)
8.37 (8.43)
8.41 (8.54)
8.22 (8.28)
7.65 (7.75)
6.12 (6.07)
8.09 (8.19)
Loss of two Schiff
base ligand molecules
Assignment
Metal oxide

1761
AMBIT THAKAR et al.
The first stage decomposition is obtained in the temperature range 140-210 °C.
The % weight loss in this range is corresponds the loss of two coordinated water
molecules15-17. The second stage decomposition is obtained in the temperature range
210-400 °C. The % weight loss in this range is corresponds % weight loss of two
Schiff base ligands.
The third stage decomposition range is obtained in the temperature range 400-900 °C.
The % weight loss in this range is corresponds % weight loss of metal oxide residue.
Thermogravimetric analysis of Cr(III) complexes
The thermograms of all Cr(III) metal complexes show two stage decompositions are listed in
Table 6. All the metal complexes do not show % weight loss below 205 °C suggest the
absence of coordinated and/or lattice water molecule/molecules.
Table 6. Thermo analytical results of Cr(III) complexes of Schiff base ligand L and ligand L1
[<205 °C]
Stage-I [205-400 °C] Stage-II [400-900 °C]
Compounds
Mass Lose
Obs. (Calc.)
Mass Lose
Obs. (Calc.)
Mass Lose
Obs. (Calc.)
[Cr(L)3]
[Cr(L1)3]
Not Observed
Not Observed
95.36 (95.48)
95.49 (95.62)
5.79 (5.83)
5.59 (5.65)
Absence of
coordinated water
molecules
Loss of three Schiff
base ligand
molecules
Assignment
Metal Oxide
The first and second stage decomposition in the thermogram curves shows the removal
of three Schiff base ligands.
The decomposition temperatures (>250 °C) of the metal complexes indicate that they
are thermally quite stable, suggesting strong metal-ligand bonding18. All the metal
complexes show further weight loss beyond 250 °C, which may be due to the weight loss of
organic matter (ligand), leaving metal(II) or metal(III) oxide as the final product of the
thermal decomposition19.
Antibacterial activity
In recent years, nitrogen heterocyclic compounds have gained importance on account of
their varied types of biological activities20-22 pyrazole derivatives have been reported to
possess antidiuretic23, antihelminthic24, hypoglycaemic, fungicidal, antituberculotic25,
antineoplastic26 and antifertility27 activities.
The effect of the ligands and their metal complexes in the growth media were
investigated by standard microbiological parameters. Concentration of the test
compounds were kept constant (500 ppm) during all the experiments. The bacterial,
fungal and yeast cultures were maintained on nutrient-agar, potato dextrose-agar and
YEDP culture-tubes (slants) respectively and were sub cultured every fortnight and
stored at 0-5 °C temperature.
The compounds were tested in vitro for the antibacterial activity against Bacterial
[Escherichia coli, Bacillus subtilis and S. aureus] and fungal [A.niger] and yeast
[S. cerevisiae] cultures with both ligands and their metal complexes using Agar cup assay
method.

Synthesis, Spectroscopic and Antimicrobial Studies
1762
The degree of effectiveness was measured by determining the diameters of the zone of
inhibition caused by the compounds. Effectiveness was classified into three zones on the
bases of their diameter of zone of inhibition.
+++
++
+
: Most effective
: Moderate effective
: Slightly effective
: Non effective
-
Most of the compounds were active against both gram (-) negative and gram (+)
positive bacteria. The results are presented in Table 7.
Table 7. Antimicrobial activity of Schiff base ligand L, ligand L1 and their metal complexes
Compounds
E. coli
+
B. subtillis
+
S. aureus
S. cerevisiae
A. niger
+
[L]
[Cr(L)3]
+
+
++
+ +
+
+ +
+ +
+
+
+ +
+
+ +
+ +
+ +
++
+
+ +
+ +
+ +
+ +
+
+ +
+
+ +
++
+ +
+ +
+
+
++
+
+ +
+ +
+
[Mn(L)2(H2O)2]
[Fe(L)2(H2O)2]
[Co(L)2(H2O)2]
[Ni(L)2(H2O)2]
[Cu(L)2(H2O)2]
[L1]
+
+
+
[Cr(L1)3]
+ +
+ +
++
+ +
+ +
+
+
+ +
+
+ +
+
+
+ +
+
+
++
+ +
+ ++
+
+ +
+ +
++
++ +
+
[Mn(L1)2(H2O)2]
[Fe(L1)2(H2O)2]
[Co(L1)2(H2O)2]
[Ni(L1)2(H2O)2]
[Cu(L1)2(H2O)2]
+ +
+++
+ +
+ ++
++
+ +
The Schiff base ligand L without metal is slightly effective against all strains of
microorganisms.
•
•
•
•
•
•
The Cr(III) metal complex is slightly effective against S. aureus & A. niger and
moderately effective against E. coli, B. subtilis and S. cerevisiae.
The Mn(II) metal complexes are slightly effective against B. subtilis & S. cerevisiae
and moderately effective against E. coli, S. aureus and A. niger.
The Fe(II) metal complex is slightly effective against A. niger and moderately effective
against E .coli, B. subtilis S. aureus and S. cerevisiae.
The Co(II) metal complex is slightly effective against S. aureus and moderately
effective against E. coli, B. subtilis, S. cerevisiae and A. niger.
All the Ni(II) metal complexes are moderately effective against E. coli, B. subtilis, S.
aureus, S. cerevisiae and A. niger.
The Cu(II) metal complexes are slightly effective against E. coli & A. niger and
moderately effective against B. subtilis, S. aureus and S. cerevisiae.
The Schiff base ligand L1 without metal is slightly effective against all strains of
microorganisms.
•
•
The Cr(III) metal complex is slightly effective against B. subtilis & S. cerevisiae and
moderately effective against E. coli, S. aureus and A. niger.
The Mn(II) metal complexes are slightly effective against S. aureus & S. cerevisiae and
moderately effective against E. coli, B. subtilis and A. niger.

1763
AMBIT THAKAR et al.
•
•
•
•
The Fe(II) metal complexes are moderately effective against E.coli, S. aureus S.
cerevisiae & A. niger and mostly effective against B. subtilis.
The Co(II) metal complex is slightly effective against S. aureus when moderately
effective against E. coli, B. subtilis & S. cerevisiae and mostly effective against A. niger.
The Ni(II) metal complexes are slightly effective against S. aureus & A. niger when
moderately effective against E. coli and mostly effective against B. subtilis and S. cerevisiae.
The Cu(II) metal complexes are slightly effective against E.coli & S. cerevisiae when
moderately effective against B. subtilis, S. aureus and A. niger.
Conclusion
On the basis of these results obtained for elemental analysis, infrared spectra, electronic
spectra, TGA analysis and magnetic susceptibility measurements the following structures
are proposed for the complex compounds of both ligands.
CH3
N
Cl
CH3
H3C
H2O
N
O
S
N
M
N
O
N
OH2
N
CH3
S
N
Cl
H3C
H3C
N
Where M= Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)
Figure 9. Structure of Complexes of the ligand
H3C
CH3
N
Cl
CH3
H3C
H2O
N
O
S
N
M
N
O
N
OH2
N
S
N
Cl
CH3
H3C
N
H3C
CH3
Where M= Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)
Figure 10. Structure of Complexes of the ligand L
The synthesized metal complexes in comparison to the uncomplexed Schiff base ligand
were screened for their antibacterial activity against pathogenic bacteria species (Escherichia
coli, Bacillus subtilis, S. aureus, A. niger and S. cerevisiae). The activity of the Schiff base

Synthesis, Spectroscopic and Antimicrobial Studies
1764
complexes became more pronounced when coordinated with metal ions. The biological
activity of the complexes follow the order Co(II)=Ni(II)> Mn(II), Fe(III), Cu(II).
Acknowledgments
The authors wish to express their gratitude to Dahod Anaj Mahajan Sarvjanik Education
Society for laboratory facilities, Principal N.V Patel Science College, V.V Nagar, Anand,
Zydus Cadila, Ahmedabad for spectral analysis.
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