Studies on chromium(III) complexes with active nitrogen, oxygen and sulfur donor ketimines synthesized under microwave conditions

Article abstract of DOI:10.1080/17415993.2010.513438

Heterocyclic ketimines, 1-(2-furanyl)ethanonehydrazincarbothioamide (L ¹H), 1-(2-furanyl)ethanone- hydrazincarboxamide (L²H), 1-(2-thienyl)ethanone hydrazincarbothioamide (L³H) and 1-(2-thienyl) ethanonehydrazincarboxamide (L⁴H), were prepared by the condensation of thiosemicarbazide and semicarbazide hydrochloride (in the presence of sodium acetate) in ethanol with the respective ketones by using microwave as well as conventional methods. Chromium(III) complexes have been prepared by mixing CrCl₃ 6H₂O in 1:1 and 1:2 molar ratios with monobasic bidentate ketimines. The authenticity of the ligands and their complexes has been established by elemental analyses, melting point determinations, molecular weight determinations, EPR, infrared and UV spectral and X-ray powder diffraction studies. These studies showed that the ligands coordinated to the metal atom in a monobasic bidentate mode, coordinating through the nitrogen and sulfur/oxygen donor system. Thus, an octahedral environment around the metal atoms has been proposed. The growth-inhibiting potential of the ligands and complexes has been assessed against a variety of fungal and bacterial strains.

Full text of DOI:10.1080/17415993.2010.513438

Journal of Sulfur Chemistry
Vol. 31, No. 6, December 2010, 515–524
Studies on chromium(III) complexes with active nitrogen,
oxygen and sulfur donor ketimines synthesized under
microwave conditions
Sumit Shrivastava, Nighat Fahmi and R.V. Singh*
Department of Chemistry, University of Rajasthan, Jaipur-302004, India
(Received 14 July 2009; final version received 31 July 2010)
Heterocyclic ketimines, 1-(2-furanyl)ethanonehydrazincarbothioamide (L1H), 1-(2-furanyl)ethanone-
hydrazincarboxamide (L2H), 1-(2-thienyl)ethanone hydrazincarbothioamide (L3H) and 1-(2-thienyl)
ethanonehydrazincarboxamide (L4H), were prepared by the condensation of thiosemicarbazide and semi-
carbazide hydrochloride (in the presence of sodium acetate) in ethanol with the respective ketones by
using microwave as well as conventional methods. Chromium(III) complexes have been prepared by mix-
ing CrCl3 · 6H2O in 1:1 and 1:2 molar ratios with monobasic bidentate ketimines. The authenticity of the
ligands and their complexes has been established by elemental analyses, melting point determinations,
molecular weight determinations, EPR, infrared and UV spectral and X-ray powder diffraction studies.
These studies showed that the ligands coordinated to the metal atom in a monobasic bidentate mode, coor-
dinating through the nitrogen and sulfur/oxygen donor system. Thus, an octahedral environment around
the metal atoms has been proposed. The growth-inhibiting potential of the ligands and complexes has been
assessed against a variety of fungal and bacterial strains.
Keywords: chromium(III) complexes; heterocyclic ketimines; spectral studies; antimicrobial activity
1. Introduction
Increasing attention for environmental protection during the last decades has led both modern aca-
demic and industrial groups to develop chemical processes with the maximum yield and minimum
cost while using non-toxic reagents, solvents and catalysts (1). Microwave (MW) synthesis rep-
resents one of the important dimensions of modern chemistry attracting a considerable amount of
attention (2). Metal complexes, in particular of transition metal ions, are important in many areas
of science, including catalysis, medicine (diagnosis and therapy), design of high value materials,
analytical chemistry and as model compounds with the structure and function of metalloproteins
(3, 4). The metal oxidation state, the type and number of donor atoms, as well as their relative
disposition within the ligand, are major factors determining the structure–activity relationship of
the metal complexes (5). Chromium(III) is a unique transition metal, which has been established
*Corresponding author. Email: rvsjpr@hotmail.com
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2010 Taylor & Francis
DOI: 10.1080/17415993.2010.513438
http://www.informaworld.com

516 S. Shrivastava et al.
to be biologically significant at all the levels of living organisms (6). Out of the two stable oxi-
dation states of chromium, chromium(III) has been shown to play a positive role in controlling
carbohydrate and lipid metabolism (7). For instance, even at the prokaryotic level, chromic chlo-
ride has been shown to maintain the glucose levels in the yeast, Saccharomyces cerevisiae (8).
Ketimine complexes of chromium(III) are efficient inhibitors for the pathogenic microorganism
and have invasive potential of Shigella dysenteriae (9). Thiosemicarbazones usually act as chelat-
ing ligands with the transition metal ion, bonding through the sulfur and azomethine nitrogen
atoms. The chemistry of thiosemicarbazones has received considerable attention in view of their
variable bonding modes, promising biological implications, structural diversity and ion-sensing
ability (10). Semicarbazones and thiosemicarbazones have been used as drugs and are reported to
possess a wide variety of biological activities against bacteria, fungi and certain types of tumors,
and they are also a useful model for bioinorganic processes (11).
Because of the wide range of medicinal applications of semicarbazones and thiosemicarbazones
and their abilities to coordinate with the transition metal ions, it is highly desirable to synthesize
and characterize the transition metal complexes with such ketimines. Keeping all these facts under
consideration during the present investigations, we have synthesized, characterized and screened
the biologically potent ligands and their chromium(III) complexes against a variety of pathogenic
fungal and bacterial strains.
2. Results and discussion
The resulting chromium(III) complexes are green solids, soluble in MeOH, DMF and DMSO
and sparingly soluble in H2O. Molecular weight determinations indicate their monomeric nature.
The reactions of CrCl3 · 6H2O with the ligands were carried out in unimolar and bimolar ratios
in methanol. The successive replacement of chloride resulted in the formation of products
[CrCl2(L)(H2O)2] and [(CrCl(L)2(H2O)] as shown in Equations (1) and (2).
1:1
CrCl3 · 6H2O + LH + NaOH −→ [CrCl2(L)(H2O)2] + NaCl + 5H2O
(1)
(2)
MeOH
1:2
MeOH
CrCl3 · 6H2O + 2LH + 2NaOH −→ [(CrCl(L)2(H2O)] + 2NaCl + 7H2O.
The physical properties and analytical data of the ligands and their metal complexes, synthesized
by green chemical approach as well as conventional method, are enlisted in Tables 1 and 2.
2.1. Electronic spectra
The electronic spectra of the complexes were recorded in DMSO. In the electronic spectra of
chromium(III) complexes, three transitions are expected and are also observed experimentally. A
4
consistent treatment for the bands is to assign the band near 15,550–17,900 cm−1 as the 4A2g →
T2g (ν1) transition; the band at 22,850–24,040 cm−1 as the 4A2g → T1g (ν2) transition and that
4
at 32,700–30,080 cm−1 as the 4A2g → T1g (P) (ν3) transition. These three transitions suggest an
4
octahedral geometry around the Cr+3 ion (12, 13). Various ligand field parameters such as Dq, B,
and β have been calculated and given in Table 3. The energy of the first spin-allowed transition
[4A2g(F) → T2g (F)] directly gives the value of 10Dq. The ligand field spectral parameters for
4
chromium(III) complexes are found to be Dq = 1790–1680 cm−1, B = 471–882 cm−1 and β =
0.51–0.96. The reduction in the Racah parameter (B) from the free-ion value of 918–654 cm−1
and the value of β indicate the covalent nature of the chromium(III) complexes.

Journal of Sulfur Chemistry 517
Table 1. Analytical data and physical properties of the ligands and their complexes synthesized by conventional heating.
Found (calculated) (%)
Molecular
Melting
weight found
Compounds
Color
Brown
White
Yellow
White
Green
Green
Green
Green
Green
Green
Green
Green
point (◦C)
C
H
N
S
M
–
(calculated)
L1H
108–110
160–162
45.01
(45.88)
49.95
4.87
(4.91)
4.96
22.09
(22.93)
25.71
16.99
(17.50)
–
186.30
(183.23)
169.75
L2H
–
(50.29)
41.85
(42.18)
45.01
(45.88)
24.14
(24.62)
34.77
(35.78)
25.96
(25.84)
38.78
(38.11)
22.66
(23.52)
32.45
(5.42)
4.21
(4.55)
4.42
(4.95)
3.67
(3.54)
3.92
(3.86)
3.51
(3.72)
3.75
(4.14)
2.84
(3.38)
3.10
(25.14)
20.90
(21.08)
22.15
(22.93)
11.84
(12.03)
17.98
(17.03)
10.80
(11.08)
15.78
(15.30)
12.03
(12.11)
16.07
(167.09)
205.37
(199.30)
185.32
(183.23)
343.32
(341.14)
471.31
(469.89)
329.25
(325.07)
496.36
(491.26)
360.46
(357.01)
505.34
L3H
130–132
32.96
(32.17)
17.18
(17.50)
10.97
(9.39)
13.06
(13.64)
–
–
L4H
187–190
–
[CrCl2(L1)(H2O)2]
[CrCl(L1)2(H2O)]
[CrCl2(L2)(H2O)2]
[CrCl(L2)2(H2O)
[CrCl2(L3)(H2O)2]
[CrCl(L3)2(H2O)]
[CrCl2(L4)(H2O)2]
[CrCl(L4)2(H2O)]
140–143
15.44
(15.29)
10.91
(11.07)
16.10
(16.18)
10.13
(10.97)
14.86
(14.56)
10.72
(10.37)
15.00
(15.29)
11.79
160–164
262–265 (d)
223–225 (d)
180–200 (d)
215–225 (d)
190–200 (d)
150–160 (d)
–
17.52
(17.97)
25.17
(25.54)
9.86
(33.49)
23.43
(24.64)
36.21
(3.61)
3.88
(3.52)
3.13
(16.74)
12.25
(12.69)
18.09
(501.03)
346.34
(341.14)
471.19
(9.39)
13.11
(35.84)
(3.86)
(17.88)
(13.65)
(11.07)
(469.90)
Note: d, decomposition.
Table 2. Analytical data and physical properties of the ligands and their complexes synthesized by MW method.
Found (calculated) (%)
Molecular
Melting
weight found
(calculated)
Compounds
Color
Brown
White
Yellow
White
Green
Green
Green
Green
Green
Green
Green
Green
point (◦C)
C
H
N
S
M
–
L1H
108–110
160–162
45.12
(45.88)
50.15
4.97
(4.91)
5.89
22.87
(22.93)
25.10
17.46
(17.50)
–
184.51
(183.23)
168.99
L2H
–
(50.29)
41.83
(42.18)
46.01
(45.88)
24.54
(24.62)
34.77
(35.78)
25.92
(25.84)
37.74
(38.11)
23.66
(23.52)
32.99
(5.42)
4.52
(4.55)
4.88
(4.95)
3.60
(3.54)
3.05
(3.86)
3.01
(3.72)
3.97
(4.14)
3.05
(3.38)
3.58
(25.14)
21.45
(21.08)
22.91
(22.93)
12.56
(12.03)
17.00
(17.03)
11.24
(11.08)
15.16
(15.30)
12.19
(12.11)
16.57
(167.05)
200.55
(199.30)
185.90
(183.23)
342.22
(341.14)
470.76
(469.89)
327.42
(325.07)
492.25
(491.26)
359.92
(357.01)
503.64
L3H
130–132
32.12
(32.17)
17.38
(17.50)
9.31
(9.39)
13.46
(13.64)
–
–
L4H
187–190
–
[CrCl2(L1)(H2O)2]
[CrCl(L1)2(H2O)]
[CrCl2(L2)(H2O)2]
[CrCl(L2)2(H2O)
[CrCl2(L3)(H2O)2]
[CrCl(L3)2(H2O)]
[CrCl2(L4)(H2O)2]
[CrCl(L4)2(H2O)]
140–143
15.78
(15.29)
11.15
(11.07)
16.09
(16.18)
10.81
(10.97)
14.72
(14.56)
10.21
(10.37)
15.33
(15.29)
10.95
160–164
262–265 (d)
223–225 (d)
180–200 (d)
215–225 (d)
190–200 (d)
150–160 (d)
–
17.83
(17.97)
25.68
(25.54)
9.46
(33.49)
24.43
(24.64)
35.11
(3.61)
3.49
(3.52)
3.37
(16.74)
12.69
(12.69)
17.29
(501.03)
343.83
(341.14)
470.88
(9.39)
13.69
(35.84)
(3.86)
(17.88)
(13.65)
(11.07)
(469.90)
Note: d, decomposition.

518 S. Shrivastava et al.
Table 3. Electronic spectral data (cm−1) of the chromium(III) complexes.
Spectral bands
Compounds
Transitions
cm−1 (nm)
Dq
B◦
β = B/B◦
ν2/ν1
4
[CrCl2(L1)(H2O)2]
4A2g(F) → T2g (F)
16,800 (595)
23,100 (432)
30,080 (332)
1680
617
0.67
1.37
4A2g(F) → T1g (F)
4
4
4A2g(F) → T1g (P)
4
[CrCl(L1)2(H2O)]
[CrCl2(L2)(H2O)2]
[CrCl(L2)2(H2O)]
[CrCl2(L3)(H2O)2]
[CrCl(L3)2(H2O)]
[CrCl2(L4)(H2O)2]
[CrCl(L4)2(H2O)]
4A2g(F) → T2g (F)
17,340 (576)
23,950 (417)
32,050 (312)
1734
1555
1754
1790
1721
1739
1704
651
882
635
471
552
563
563
0.70
0.96
0.69
0.51
0.60
0.61
0.61
1.38
1.47
1.37
1.28
1.33
1.34
1.34
4A2g(F) → T1g (F)
4
4
4A2g(F) → T1g (P)
4
4A2g(F) → T2g (F)
15,550 (643)
22,995 (434)
30,314 (329)
4A2g(F) → T1g (F)
4
4
4A2g(F) → T1g (P)
4
4A2g(F) → T2g (F)
17,540 (570)
24,040 (415)
32,356 (309)
4A2g(F) → T1g (F)
4
4
4A2g(F) → T1g (P)
4
4A2g(F) → T2g (F)
17,900 (553)
23,050 (433)
31,500 (317)
4
4A2g(F) → T1g (F)
4A2g(F) → T1g (P)
4
4
4A2g(F) → T2g (F)
17,210 (581)
23,000 (434)
30,300 (330)
4
4A2g(F) → T1g (F)
4A2g(F) → T1g (P)
4
4
4A2g(F) → T2g (F)
17,380 (575)
23,290 (429)
32,700 (306)
4A2g(F) → T1g (F)
4
4A2g(F) → T1g (P)
4
4
4A2g(F) → T2g (F)
17,035 (586)
22,850 (436)
31,780 (315)
4A2g(F) → T1g (F)
4
4A2g(F) → T1g (P)
4
Note: B, Complex; Bo, free ion.
2.2. ESR spectra and magnetic moment
The electron spin resonance spectra of 1:1 and 1:2 chromium(III) complexes were recorded at
room temperature. These consist of a single broad peak in each case and from which the Lande
splitting factor (“g” values) has been calculated which lie in the range 1.9289–1.9431, with giso
(2.04) which are characteristic of an octahedral geometry (14). The room temperature magnetic
momentforthechromium(III)chelatesisslightlylessthantherequiredenvironment.Theobserved
magnetic moment value of 3.92–4.20 BM and the electronic spectra of the complexes support the
octahedral structure of the complexes (15).
2.3. Infrared spectra
The infrared (IR) spectra of the thiosemicarbazones (L1H and L3H) and semicarbazones (L2H and
L4H) display a sharp band at 1610–1600 cm−1, which is shifted to a lower frequency, in the spectra
ofthecorrespondingmetalcomplexes, probablyduetothecoordinationoftheazomethinenitrogen
to the metal atom. In the spectra of the free ligands, bands appearing due to ν(NH) vibrations in the
regions 3240–3230 cm−1disappear in the spectra of the complexes, indicating deprotonation of the
=
=
functional groups on complexation. Medium-intensity bands due to ν(C S)/ν(C O) vibrations
appearintheregions1050–1040/1690–1680 cm−1 inthespectraofligandsandshiftedtothelower
frequencyinthespectraofthecomplexes.Thisfactisfurthercorroboratedbytheobservationofthe
new bands due to ν(C–O) and ν(C–S) modes at lower frequency in the spectra of chromium(III)

Journal of Sulfur Chemistry 519
complexes. In the spectra of chromium(III) complexes, a band is observed in the range 870–
860 cm−1, which may be attributed to the coordinated water molecule. Further, a broad band
around3480–3400 cm−1maybedueto ν(O–H)ofwatermolecule.ThefarIRspectraofthesemetal
complexes exhibited new bands, which are not present in the spectra of the ligands. The single
band observed at ca. 320–315 cm−1 is due to ν(Cr–Cl), suggesting thereby that the complexes
have a trans structure (16) and the presence of ν(Cr–N), ν(Cr–S) (17) and ν(Cr–O) vibrations
around 535 10, 360–335 and 610 10 cm−1 indicate that complexation takes place through
the nitrogen and sulfur/oxygen atoms.
2.4. NMR spectra (1H and 13C)
The proposed structures of the ligands get further support by the 1H NMR and 13C spectra of the
1
ligands. The significant H NMR and 13C NMR spectral data of the ligands, (L1H, L2H, L3H)
and (L4H) along with their tentative assignments are reported in Table 4.
On the basis of above studies, octahedral environment around the metal atoms has been
proposed, and the expected structures are as shown in Figures 1 and 2.
Table 4. 1H NMR and 13C NMR spectral data (δ, ppm) of the ligands.
1H NMR spectra (δ, ppm)
CH3
13C NMR spectra (δ, ppm)
N
C
NH
NH2
Aromatic Azomethine Amido/thiolo Methyl
Ligands
L1H
proton
proton proton
protons
carbon
178.51
160.07
146.2
carbon
198.71
177.35
179.78
178.62
carbon Aromatic carbon
1.8
9.9
2.83
2.55
2.81
2.84
7.80–6.60
7.89–6.32
8.68–7.16
7.84–7.20
12.3
150.81, 134.75,
114.74, 146.14
153.02, 144.19,
139.80, 112.17
143.40, 128.54,
128.05, 128.91
140.31, 126.45,
126.70, 125.37
L2H
1.78
1.68
2.3
10.68
10.68
10.68
12.33
13.74
13.17
L3H
L4H
152.76
Cl
C
S
OH2
OH2
N
N
Cr
C
CH3
R
Cl
Figure 1. Suggested structures for chromium(III) complexes. 1:1 complex.
H3C
H2O
R
C
H2N
N
C
S
N
Cr
Cl
N
C
S
N
NH2
C
R
CH3
Figure 2. Suggested structures for chromium(III) complexes. 1:2 complex.

520 S. Shrivastava et al.
2.5. X-ray powder diffraction study
The possible lattice dynamics of the finely powdered product, [CrCl2(L1)(H2O)2], has been
deduced on the basis of X-ray powder diffraction studies. The observed interplanar spacing values
(“d” in Å) have been measured from the diffractogram of the compound (Figure 3); the Miller
indices h, k and l have been assigned to each d value and 2θ angles are reported in Table 5.
The results show that the compound belongs to “orthorhombic” crystal system having unit cell
parameters as a = 9.63, b = 17.37 c = 21.15, maximum deviation of 2θ = 0.045◦ and α = 90◦,
β = 90◦, γ = 90◦.
Figure 3. X-ray powder diffraction spectra of [CrCl2(L1)(H2O)2].
Table 5. X-ray diffraction data of [CrCl2(L1)(H2O)2].
2θ (◦)
(Exp.)
2θ (◦)
(Calc.)
2θ (◦)
(Diff.)
d (Å)
(Exp.)
d (Å)
(Calc.)
Intensity
(Exp.)
h
k
l
0
0
1
2
0
1
1
1
4
0
0
4
3
0
4
1
3
6
3
6
2
4
3
0
0
5
0
6
2
1
7
5
4
4
10
9
3
1
1
0
0
10
1
4
26.451
32.335
34.071
36.597
39.450
41.464
43.953
46.456
52.903
54.543
55.907
57.379
59.402
60.571
63.135
69.016
72.604
74.475
75.695
78.595
81.164
82.679
84.116
86.162
26.476
32.380
34.030
36.650
39.475
41.468
43.995
46.469
52.922
54.514
55.896
57.386
59.407
60.526
63.106
69.034
72.610
74.494
75.701
78.568
81.134
82.694
84.105
86.150
−0.025
−0.045
0.041
−0.008
−0.025
−0.004
−0.042
−0.013
−0.019
0.028
4.23388
3.47874
3.30634
3.08518
2.86999
2.73629
2.58840
2.45603
2.17456
2.11358
2.06641
2.01772
1.95499
1.92072
1.85032
1.70980
1.63610
1.60074
1.57861
1.52984
1.48945
1.46627
1.44614
1.41830
4.23000
3.47400
3.31020
3.08453
2.86825
2.73607
2.58604
2.45537
2.17384
2.11500
2.06677
2.01750
1.95482
1.92201
1.85106
1.70941
1.63598
1.60040
1.57861
1.52984
1.48945
1.46627
1.44614
1.41830
13.07
−3.94
6.16
8.59
35.84
8.29
28.41
7.68
2.91
5
0
4
6
2
5
6
1
0
4
4
7
9
6
10
4
0
9
1
3
8
1
6
4.88
0.011
11.49
28.30
9.48
4.79
5.82
6.13
11.05
7.37
14.29
7.01
5.17
−0.007
−0.005
0.045
0.028
−0.018
−0.006
−0.019
−0.006
0.027
4
13
6
13
13
0.030
−0.014
5.74
4.87
7.99
0.011
0.012

Journal of Sulfur Chemistry 521
2.6. Antimicrobial assay
The heterocyclic ketimines and their chromium(III) complexes were evaluated for their antimi-
crobial activity against two bacteria Bacillus subtilis (Gram-positive) and Escherichia coli
(Gram-negative) and two fungi Candida albicans andAspergillus niger and the results are summa-
rized in Table 6. The ligands were found to be biologically active and the chromium complexes are
more active than their respective ligands. This indicated that the complexation to metal enhances
the activity of the ligand. This may be explained by Tweedy’s chelation theory (18), according
to which chelation reduces the polarity of the central metal atom because of partial sharing of its
positive charge with the ligand, due to which the lipophilic character of the metal chelate increases
and favors its permeation through the lipid layer of cell membrane. It has also been proposed that
the ultimate action of the compounds is the denaturation of one or more proteins of the cell as a
result of which normal cellular processes are impaired (19).
3. Conclusions
MW irradiation is an efficient and environmentally benign method to accomplish various inorganic
syntheses to afford purer products in higher yields in shorter reaction periods. All the ligands
behave as a monofunctional bidentate with metal ion in different reaction conditions. Based on
the analytical and spectral data, a hexacoordinated environment around the metal ion has been
proposed. The antimicrobial activity of the complexes and the ligands showed that the complexes
are more active than the parent ligands.
4. Experimental
The CrCl3·6H2O was purchased from Alfa aesar. All the reagents were dried and distilled before
use. 2-Acetylfuran and 2-acetylthiophene were purchased and used as received. All preparations
were done under anhydrous conditions.
Table 6. Antifungal and antibacterial screening data for the ligands and their complexes.
(Antibacterial activity) Diameter (mm)
(Antifungal activity) (%) Inhibition
after 96 h (concentration in ppm)
of inhibition zone after 24 h
(concentration in ppm)
C. albicans
A. niger
B. subtilis
E. coli
1000
Compounds
50
100
200
50
100
200
500
1000
500
L1H
28
27
28
25
30
32
29
32
30
33
29
31
50
47
44
46
42
49
50
49
52
51
53
48
51
85
50
52
53
51
55
59
54
60
59
62
57
59
100
25
24
26
23
28
29
28
30
31
32
27
30
52
32
30
33
30
35
38
36
42
37
44
35
40
89
52
53
53
50
56
59
56
65
58
66
57
60
99
11
10
11
11
13
14
12
14
12
15
13
14
–
13
11
14
12
14
15
13
13
15
16
15
16
–
10
8
10
9
11
12
11
12
12
13
11
12
–
11
9
L2H
L3H
13
11
14
15
13
14
16
16
13
15
–
L4H
[CrCl2(L1)(H2O)2]
[CrCl(L1)2(H2O)]
CrCl2(L2)(H2O)2]
[CrCl(L2)2(H2O)]
[CrCl2(L3)(H2O)2]
[CrCl(L3)2(H2O)]
CrCl2(L4)(H2O)2]
[CrCl(L4)2(H2O)]
Nystatin (standard
fungicide)
Streptomycin (standard
bactericide)
–
–
–
–
–
–
16
18
15
18

522 S. Shrivastava et al.
4.1. Preparation of the ligands
Two different routes were employed for the synthesis of the ligands.
(1) In MW-assisted synthesis, the ligands, thiosemicarbazones (L1H, L3H) and semicarbazones
(L2H, L4H), were prepared by the condensation of 2-acetylfuran and 2-acetylthiophene with
thiosemicarbazide and semicarbazide hydrochloride (in the presence of sodium acetate),
respectively, in 1:1 molar ratio through a conventional MW oven by taking 2–4 ml of ethanol
as a solvent. The reactions were completed in a short period of 4–7 min.
(2) For comparison purpose, the above ligands were also synthesized by a thermal method
as described previously (20). The parent ligands exist in the tautomeric forms depicted in
Figure 4. A comparison between thermal method and MW method is given in Table 7.
X
C
XH
C
H3C
R
H3C
R
C
N
C
N
N
NH2
N
NH2
H
Ketonic form
Enolic form
4.2. Preparation of the complexes
The complexes were also prepared by two different routes.
(1) In MW-assisted synthesis, the complexes were prepared by irradiating the reaction mixture
of chromium trichloride and the respective ligand in appropriate stoichiometric proportions
using NaOH in dry methanol. The products were recovered from the MW oven and dissolved
in a 2–5 ml of dry methanol, where the precipitate of sodium chloride formed during the
course of the reaction was removed by filtration and the filtrate was then concentrated under
(L1H and L2H)
R =
O
(L3H and L4H)
S
Figure 4. Structure of the ligands.
Table 7. Comparison between MW and thermal method.
Yield (%)
Thermal
Solvent (ml)
Time
Thermal (h)
Compounds
MW
Thermal
MW
MW (m)
L1H
80
79
80
80
76
73
70
72
69
75
70
74
87
89
86
88
83
87
89
86
87
81
84
80
100
100
100
100
50
35
30
40
55
4
3
3
2
5
2
3
2
2
5
2
3
4
4
4.5
3.5
15
15
14
13
12
15
14
15
5
4
7
5
4
7
5
5
4
7
7
4
L2H
L3H
L4H
[CrCl2(L1)(H2O)2]
[CrCl(L1)2(H2O)]
[CrCl2(L2)(H2O)2]
[CrCl(L2)2(H2O)]
[CrCl2(L3)(H2O)2]
[CrCl(L3)2(H2O)]
[CrCl2(L4)(H2O)2]
[CrCl(L4)2(H2O)]
30
30
40

Journal of Sulfur Chemistry 523
reduced pressure. The resulting compounds were washed with cyclohexane and recrystallized
with methanol.
(2) These complexes were also synthesized by the thermal method where instead of 4–7 min,
reactions were completed in 12–15 h and the yield of the products was also less than that
obtainedbytheMW-assistedsynthesis. Inthismethod, themethanolicsolutionofCrCl3·6H2O
was added to the methanolic solution of ligands in 1:1 and 1:2 molar ratios using NaOH in
appropriate stoichiometric proportions. The resulting mixture was heated under reflux for
12–15 h, filtered to remove NaCl and the solvent was concentrated under reduced pressure.
The product was dried in vacuum. The resulting compounds were washed with cyclohexane
and recrystallized with methanol.
4.3. Physical measurements and analytical methods
The molecular weights were determined by the Rast Camphor method (21). The metal contents
were analyzed gravimetrically. Sulfur and nitrogen were determined by Messenger’s (22) and
Kjeldahl’s methods (23), respectively. Carbon and hydrogen analyses were performed at the
CDRI, Lucknow. IR spectra were recorded on a Nicolet Megna FTIR-550 spectrophotometer
using KBr pellets. The electronic spectra were recorded on a Varian–Cary/5E spectrophotometer
at SAIF, IIT Madras, Chennai. EPR spectra of the complexes were monitored on Varian E-4X
band spectrometer at SAIF, IIT Madras, Chennai.
4.4. Antifungal screening
The antifungal activity of the ligands and their chromium complexes was tested by agar plate
technique (24) against the two pathogenic fungi C. albicans and A. niger using the potato dextrose
agar medium having the composition: glucose 20 g, starch 20 g, agar–agar 20 g and distilled water
1000 ml. Solutions of the test compounds in methanol at 50, 100 and 200 ppm concentrations
were prepared and then were mixed with the medium. The medium then was poured into Petri
plates and the spores of fungi were placed on the medium with the help of inoculum’s needle.
These Petri plates were wrapped in the polythene bags containing a few drops of alcohol and were
placed in an incubator at 25 2 ◦C. The activity was determined after 96 h of incubation at room
temperature (25 ◦C). The controls were also run and three replicates were used in each case. The
linear growth of the fungus was obtained by measuring the fungal colony diameter in Petri plates
after 4 days. The percentage inhibition was calculated as
(C − T )100
% Inhibition =
,
C
where C and T are the diameters of the fungus colony in the control and test plates, respectively.
4.5. Antibacterial screening
In vitro antibacterial screening is generally performed by disc diffusion method (25) for the
primary selection of the compounds as therapeutic agents. The method is essentially a qualitative
or a semi-quantitative test indicating the sensitivity or resistance of microorganisms to the test
materials as well as the bacteriostatic or bactericidal activity of a compound. The antibacterial
activity of the ligands and their chromium complexes was evaluated against Gram-positive (B.
subtilis) and Gram-negative (E. coli) bacteria. The nutrient agar medium having the composition:
peptone 5 g, beef extract 5 g, NaCl 5 g, agar–agar 20 g and distilled water 1000 ml was pipetted
into the Petri plates. When it solidified, 5 ml of warm seeded agar was applied. The seeded agar

524 S. Shrivastava et al.
was prepared by cooling the molten agar to 40 ◦C and then 10 ml of bacterial suspension was
added. The compounds were dissolved in methanol in 500 and 1000 ppm concentrations. Paper
discs of Whatman No. 1 filter paper 5 mm in diameter were soaked in these solutions of varied
concentrations. The discs were dried and placed on the medium previously seeded with organisms
in Petri plates at a suitable distance. The Petri plates were stored in an incubator at 28 2 ◦C
for 24 h. The diameters of the zone of inhibition produced by the compounds were compared
with the standard antibiotic (Streptomycin). The zone of inhibition thus formed around each disc
containing the test compounds was measured accurately in millimetres.
Acknowledgements
The authors are thankful to CSIR, New Delhi, and UGC, New Delhi, for financial assistance through grant no.
01(2307)/09/EMR-II and 36-1/2008(RAJ)(SR), respectively.
References
(1) Kidwai, M.; Thakur, R.; Mohan, R. Acta Chim. Slov. 2005, 52, 88–92.
(2) Kobayashi, S.; Manabe, K. Acc. Chem. Res. 2002, 35, 209–217.
(3) Yoshikawa,Y.; Ueda, E.; Kawabe, K.; Miyabe, K.; Takino, T.; Sakurai, H;. Kojima,Y. J. Biol. Inorg. Chem. 2002, 7,
68–73.
(4) Glusker, J.P.; Katz, A.K.; Bock, C.W. Rigaku J. 1999, 16, 8–16.
(5) Amado, A.M.; Ribeiro-Claro, P.J.A. J. Inorg. Biochem. 2004, 98, 561–568.
(6) Juturu, V.; Komorowski, J.R. Am. J. Clin. Nutr. 2003, 78, 192–193.
(7) Ryan, G.J.; Wanko, N.S.; Redman, A.R.; Cook, C.B. Ann. Pharmacother. 2003, 37, 876–885.
(8) Zetic, V.G.; Stehlik-Tomas, V.; Grba, S.; Lutilsky, L;. Kozlek, D. J. Biosci. 2001, 26, 217–223.
(9) Yamini Shrivastava, H.; Niranjali Devaraj, S.; Unni Nair, B. J. Inorg. Biochem. 2004, 98, 387–392.
(10) Mishra, D.; Naskar, S.; Drew, M.G.B.; Chattopadhyay, S.K. Inorg. Chim. Acta 2006, 359, 585–592.
(11) Kizilcikli, I.; Ulkuseven, B.; Das¸demir, Y.; Akkurt. B. Synth. React. Inorg. Met-Org. Chem. 2004, 34, 653–665.
(12) Aranha, P.E.; dos Santos, M.P.; Romera, S.; Dockal, E.R. Polyhedron 2007, 26, 1373–1383.
(13) Dubey, R.K.; Dubey, U.K.; Mishra, C.M. Indian. J. Chem. 2008, 47A, 1208–1212.
(14) El-ajaily, M.M.; Maihub, A.A.; Hudere S.S.; Bensaber, S.M. Asian J. Chem. 2006, 18, 2427–2430.
(15) Saydam, S.; Yilmaz, E. Spectrochim. Acta A 2006, 63, 506–510.
(16) Byun, J.C.; Han Bull, C.H. J. Korean Chem. Soc. 2005, 26, 1395–1402.
(17) Shukla, D.; Gupta, L.K.; Chandra, S. Spectrochim. Acta A 2008, 71, 746–750.
(18) Tweedy, B.G. Phytopathology 1964, 55, 910–914.
(19) Lehninger, A.L. Biochemistry, 2nd ed.; Worth Publishers: New York, 1975; pp 519–520.
(20) Saxena, C.; Singh, R.V. Synth. React. Inorg. Met.-Org. Chem. 1992, 2, 1061–1072.
(21) Vogel, A.I. A Textbook of Organic Quantitative Analysis, 5th ed.; Pearson Education Ltd.: Thames Polytechnique,
London, 2004; p 243.
(22) Vogel, A.I. A Textbook of Quantitative Chemical Analysis, 6th ed.; Pearson Education Ltd.: Thames Polytechnique,
London, 2006; pp 498–499.
(23) Vogel, A.I. A Textbook of Quantitative Chemical Analysis, 6th ed.; Pearson Education Ltd.: Thames Polytechnique,
London, 2006; p 387.
(24) Fahmi, N.; Saxena, C.; Singh, R.V. Bull. Chem. Soc. Jpn. 1996, 69, 963–969.
(25) Jain, M.; Kumar, D.; Singh, R.V. Main Group Met. Chem. 2003, 26, 99–109.

Copyright of Journal of Sulfur Chemistry is the property of Taylor & Francis Ltd and its content may not be
copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.