Structural and pharmacological studies of transition metal complexes

Article abstract of DOI:10.1080/15533174.2011.591322

Chromium(III) and manganese(II) complexes were synthesized with tetra-binding chelating agent. The condensation product of 1,4- diformylpiperazine and 4-aminoantipyrine coordinate to the metal ion through nitrogen and oxygen donor sites to give the comple

Full text of DOI:10.1080/15533174.2011.591322

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Structural and Pharmacological Studies of Transition
Metal Complexes
Amit Kumar Sharma a b & Sulekh Chandra b
a Department of Chemistry , Ramjas College (University of Delhi) , Delhi, India
b Department of Chemistry , Zakir Husain College (University of Delhi) , J. L. Nehru
Marg, New Delhi, India
Published online: 04 Oct 2011.
To cite this article: Amit Kumar Sharma & Sulekh Chandra (2011) Structural and Pharmacological Studies of Transition
Metal Complexes, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:8, 923-931, DOI:
10.1080/15533174.2011.591322
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:923–931, 2011
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591322
Structural and Pharmacological Studies of Transition Metal
Complexes
Amit Kumar Sharma1,2 and Sulekh Chandra2
1Department of Chemistry, Ramjas College (University of Delhi), Delhi, India
2Department of Chemistry, Zakir Husain College (University of Delhi), J. L. Nehru Marg, New Delhi,
India
with the help of physicochemical, spectral, thermal, x-ray, and
other forms of analysis, frequently used and powerful analytical
Chromium(III) and manganese(II) complexes were synthesized
with tetra-binding chelating agent. The condensation product of
1,4-diformylpiperazine and 4-aminoantipyrine coordinate to the
metal ion through nitrogen and oxygen donor sites to give the com-
plexes having stoichiometry [M(L)X2]Xn, where M = Cr(III) and
Mn(II), L = ligand, X = NO3−, CH3COO−, and Cl−, and n =
0 or 1. The compounds were structurally studied with a number
of analytical methods like physical methods: elemental analyses,
molar conductance measurements, magnetic susceptibility mea-
surements, and spectral methods: IR, UV/visible, NMR, ESIMS,
and EPR. The studies of the compounds reveal that the ligand L
is bonded to the metal ion via ONNO binding sites. The resulting
complexes were found to have octahedral geometry. The phar-
macological studies of the compounds were examined against the
opportunistic pathogens.
tools.[10]
Views of these studies and their fruitful results encourage bio-
chemists to further explore these two class of the compounds
(piperazine and 4-aminoantipyrine) in the widespread pharma-
ceutical field. In the present studies, we have synthesized a
derivative of piperazine and 4-aminoantipyrine and its transition
metal complexes. The compounds have also been investigated
for the fungicidal studies.
EXPERIMENTAL
Materials
Keywords complexes, ligand, pharmacological investigations, spec-
All the chemicals, solvents, and metal salts are commercial
products and procured from Sigma-Aldrich, Fluka, S. D. Fine,
E. Merck, and Thomas Backer.
tral characterization
INTRODUCTION
The piperazine derivatives constitute an important class of
compounds that have diverse applications in the pharmaceuti-
cal array like anti-HIV activity, antidepressant, anxiolytic drug,
anticancerous, etc.[1–5] Moreover, 4-aminoantipyrine incorpo-
rated compounds have also been studied in the pharmaceu-
tical field and have multiple drug actions such as analgesic,
anti-inflammatory, antifungal, antibacterial, etc.[6–9] The chelat-
ing modes of the piperazines and antipyrines have been mod-
ified to have a variety of ligand systems, as they have been
used as the precursors to give interesting products on reac-
tion with substituted amines as well as carbonyl compounds.
The coordinating properties of these derivatives have also been
widely examined with transition metals as well as lanthanides
Physical Measurements
Nuclear magnetic resonance (NMR) spectra were recorded
with a model Bruker Advance DPX-300 spectrometer operating
at 300 MHz using dimethyl sulfoxide (DMSO)-d6 as a solvent
and TMS as an internal standard. Infrared (IR) spectra were
recorded as KBr/CsI pellets in the region 4000−200 cm−1 on a
Fourier transform (FT)-IR spectrum BX-II spectrophotometer.
Electrospray ionization (ESI) mass spectra were recorded on a
model Q Star XL LCMS−MS system. The stoichiometric anal-
yses were carried out on a Carlo-Erba 1106 analyzer. The elec-
tronic spectra were recorded on Shimadzu UV mini-1240 spec-
trophotometer. Electron paramagnetic resonance (EPR) spectra
were recorded as solids and solutions on an E4-EPR spectrom-
eter at room temperature as well as liquid nitrogen temperature
operating at the X-band region using diphenylpicrylhydrazyl
(DPPH) as a standard. The molar conductance of complexes
was measured in DMSO at room temperature on an ELICO
(CM 82T) conductivity bridge. The magnetic susceptibility
was measured at room temperature on a Gouy balance using
CuSO4·5H2O as calibrant.
Received 21 January 2011; accepted 17 March 2011.
The financial assistance of DRDO, New Delhi is gratefully ac-
knowledged.
Address correspondence to Sulekh Chandra, Department of Chem-
istry, Zakir Husain College (University of Delhi), J. L. Nehru Marg,
New Delhi 110002, India. E-mail: schandra 00@yahoo.com
923

924
A. K. SHARMA AND S. CHANDRA
Synthesis of Ligand 1,4-Diformylpiperazine
Bis(4-imino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one)
(Figure 1)
H2N
O
CH3
N
CH3
H
H
The requisite quantity of the 4-aminoantipyrine (0.04 mol)
was dissolved in acetonitrile (25 mL) and the solution was
heated for 15 min in the presence of 1–2 drops of conc. HCl. To
this warmed solution, a hot solution of 1,4-diformylpiperazine
(2.8432 g, 0.02 mol) in acetonitrile (15 mL) was added dropwise
with continuous stirring. The reaction mixture was refluxed for 5
h at 85◦C, allowed to stay at room temperature, and then kept in
a refrigerator overnight. The white shiny microcrystalline prod-
uct was precipitated out, filtered, washed several times with ace-
tonitrile, and dried under vacuum over P4O10. Yield 60%, m.p.
210◦C. Elemental analyses: Found (Calcd.) for C28H32N8O2:
N
C
O
N
N
C
O
2
+
1-2 drops
of conc. HCl
5h, 85oC
H
N
H
N
C, 65.58 (65.62); H, 6.21 (6.25); N, 21.82 (21.87)%. IR (cm−1
,
C
C
N
KBr pellets): 1667 (νC = O), 1606 (νC = N); 1H-NMR (300 MHz,
DMSO-d6): δ (ppm): 2.11 (s, 6H, H3C-C), 2.88 (s, 6H, H3C-
N), δ 3.24-3.48 (m, 8H, piperazine ring), 7.16-7.35 (m, 10H,
Ph), 7.97 (s, 2H, H-C = N) (Figure 2); 13C-NMR (300 MHz,
DMSO-d6): δ (ppm): 10.68 (2C, H3C-C), 35.58 (2C, H3C-N),
127.13, 128.90, 129.35, 129.61 (4C, piperazine ring), 129.66,
130.34, 130.47, 131.90, 134.59, 135.30 (6C, aromatic rings);
137.62 (2C, MeC, ring), and 138.04 (2C, N-C, ring), 150.08
(2C, C = N), 196.62 (2C, C = O) (Figure 3); ESI MS: m/z =
512 (M+), 513 (M+ + 1) isotopic, 187 (C11H11N2O+) base peak
ion with pyrazolone moiety, 15, 26, 112, 138, 325, 358, 435,
482, and 497 fragments (Figure 4).
H3C
N
CH3
H3C
N
N
CH3
O
O
N
N
FIG. 1. Synthesis of ligand.
plate to the respective control plate. DMSO and captan were
employed as a control and a standard fungicide, respectively.
Synthesis of the Complexes
The requisite amount of the ligand (1 mmol) was dissolved
in acetonitrile and the solution was heated for 10 min. To this
solution, a hot solution of metal salt (nitrate, chloride, or ac-
etate) (1 mmol) in acetonitrile was added slowly dropwise with
constant stirring. The resulting mixture was refluxed for 8–10 h
at 80–90◦C. After refluxing, the mixture was allowed to stay at
room temperature for 2 h and than cooled overnight at 0◦C. The
precipitate of the complex was separated out, filtered, washed
with cold acetonitrile, and dried under vacuum over P4O10.
RESULTS AND DISCUSSION
The reaction of the Schiff’s base ligand with the Cr(III)
and Mn(II) metal ions gave complexes having the composi-
−
tions Cr(L)X3 and Mn(L)X2, where ligand is L and X = NO3
,
CH3COO−, and Cl− ions. The physicochemical and stoichio-
metric data of the compounds are given in Table 1. The con-
ductometric studies reveal that the complexes have [Cr(L)X2]X
and [Mn(L)X2] compositions.[13] The magnetic moments lie in
the range 3.76–3.90 B.M. for Cr(III) complexes and 5.97–6.01
B.M. for Mn(II) complexes, respectively, which correspond to
the high spin nature of the complexes.
Pharmacological Studies
The food poison technique was employed to investigate the
fungicidal studies and dilution technique was used to determine
the minimum inhibitory concentration (MIC).[11,12] The stock
solutions of the compounds were prepared in DMSO solvent.
IR Spectra
The key IR bands of the synthesized compounds with their
The diluted solution of the compound to be tested was directly assignments are listed in Table 2. The IR spectrum of the ligand
added to the PDA (potato dextrose agar) medium and the mixture shows bands at 1667 and 1606 cm−1, which may be assigned
was poured into a petri plate. The petri plates were kept for a to the ν(C = O) and ν(C = N) stretching vibrations, respec-
day to check the sterility. A disc of 5 mm diameter of test fungal tively.[10,14,15] On complexation, the position of these bands is
culture was placed at the center of the petri plate with the help of altered, which reveals that the carbonyl oxygen and azomethine
an inoculum needle. The petri plates were sealed with parafilm nitrogen are bonded to the central metal ion. The IR spectra of
and incubated at 29 2◦C for a week.
complexes display the new bands centered in the range 375–401
All determinations were performed in duplicate. The results and 450–572 cm−1, which may be due to the ν(M−O) and
of the fungicidal capacity of the compounds were determined ν(M−N) stretching vibrations,[16] respectively. The appearance
in percentage terms from the growth of the fungus in the test of these additional bands also supports the bonding of ligands

925

926
A. K. SHARMA AND S. CHANDRA
FIG. 2. 1H-NMR spectrum of ligand.
to the metal ion through nitrogen and oxygen binding sites, tion of nitrate anion. The difference of the IR frequencies, ν5
and the ligand acts as a tetradentate ONNO donor. In the IR and ν1, (92−142 cm−1) indicates the coordination of NO3− ion
spectra of complexes, the bands also appear due to the coor- in unidentate fashion. The acetato complexes give IR bands at
dinated anions. The chloro complexes show IR bands in the 1428−1456 (νasym stretching vibration) and 1261−1270 cm−1
region 330−340 cm−1 due to ν(M−Cl). The nitrato complexes (νsym stretching vibration), and the ꢁν (167−186 cm−1) values
display IR bands in the regions 1390−1496 (ν5), 1298−1354 correspond to coordination of acetate anion through one donor
(ν1), and 1059−1102 cm−1 (ν2) due to NO stretching vibra- atom.[17–19]
TABLE 2
Comparative IR data of compounds
Substance number
Compound
Ligand
[Cr(L)(NO3)2]NO3
[Cr(L)Cl2]Cl
[Cr(L)(OAc)2]OAc
[Mn(L)(NO3)2]
[Mn(L)Cl2]
ν(C = N)
ν(C = O)
ν(M−O)
ν(M−N)
Anion bands
1
2
3
4
5
6
7
1606
1564
1572
1580
1626
1553
1571
1667
1637
1643
1622
1676
1638
1617
—
—
—
1496, 1354, 1059
330
1456, 1270
1390, 1298, 1102
340
401
396
412
382
393
375
572
499
507
450
510
488
[Mn(L)(OAc)2]
1428, 1261

STRUCTURAL AND PHARMACOLOGICAL STUDIES
927
FIG. 3. 13C-NMR spectrum of ligand.
TABLE 3
Electronic spectral data and ligand field parameters of complexes
Substance
number
Dq
LFSE
Complex
λmax (cm−1
)
(cm−1
)
B(cm−1
)
C(cm−1
)
β
(kJmol−1
)
F4
F2
1
2
3
4
5
6
[Cr(L)(NO3)2]NO3 17452,37735
[Cr(L)Cl2]Cl 16231,25042, 37068
[Cr(L)(OAc)2]OAc 18621,27322
1745
1623
1862
712
662
760
710
504
424
—
—
—
3286
3816
4047
0.69
0.64
0.74
0.74
0.53
0.44
250.21
232.70
266.97
—
—
—
—
—
—
—
—
—
[Mn(L)(NO3)2]
[Mn(L)Cl2]
[Mn(L)(OAc)2]
19476,23530, 28500, 34125 781
19260,24128, 27660, 37120 554
17295,24480, 27450, 35730 466
93.9 1179.4
109.0 1049.1
115.6 1002.1
TABLE 4
EPR spectral data of complexes
Polycrystalline form
Solution form
Substance
number
Complex
g (LNT) g (LNT) giso (RT) giso (LNT) giso (RT) Aiso (RT) giso (LNT) Aiso (LNT)
⊥ ꢁ
1
2
3
4
5
6
[Cr(L)(NO3)2]NO3
[Cr(L)Cl2]Cl
[Cr(L)(OAc)2]OAc
[Mn(L)(NO3)2]
[Mn(L)Cl2]
—
—
—
—
—
—
—
—
—
—
—
—
1.9872
1.9584
1.9902
2.0122
2.0006
2.0212
—
—
—
2.0451
2.0602
2.3865
—
—
—
2.0048
1.9974
2.0022
—
—
—
90.5
96.0
92.5
—
—
—
2.0193
2.0161
2.2016
—
—
—
92.5
88.5
90.0
[Mn(L)(OAc)2]

928
A. K. SHARMA AND S. CHANDRA
FIG. 4. Mass spectrum of ligand.
TABLE 5
Fungicidal screening data of the compounds
Fungicidal activity (%) (conc., µg mL−1
)
A. brassicae
A. niger
F. oxysporum
Compound
200
300
500
200
300
500
200
300
500
Ligand
[Cr(L)(NO3)2]NO3
[Cr(L)Cl2]Cl
[Cr(L)(OAc)2]OAc
[Mn(L)(NO3)2]
[Mn(L)Cl2]
[Mn(L)(OAc)2]
Standard (captan)
30
36
35
38
39
35
36
70
40
50
48
44
52
51
50
80
58
62
60
60
63
61
60
100
30
34
32
32
37
36
36
75
42
45
43
44
50
47
48
90
60
65
64
64
68
66
65
100
33
39
38
36
41
40
40
65
45
50
49
48
53
50
51
75
64
67
66
65
68
66
67
100

STRUCTURAL AND PHARMACOLOGICAL STUDIES
929
FIG. 5. EPR spectra of, (a) [Cr(L)Cl2]Cl and (b) [Mn(L)Cl2] complexes.

930
A. K. SHARMA AND S. CHANDRA
Electronic Spectra
The electronic spectral data along with ligand field pa-
rameters are presented in Table 3. The electronic spectra
of Cr(III) complexes exhibit the transitions at wavelength
16231–18621 and 25042–27322 cm−1, which may be assigned
4
4
to the 4A2g(F) → T2g(F) (ν1) and 4A2g(F) → T1g(F) (ν2) spin-
allowed d–d transitions. These transitions indicate the octahe-
dral environment around the Cr(III) metal ion.[20,21] The spectra
also display the bands at wavelength 37068–37735 cm−1, which
may be due to the charge transfer transition.
The electronic spectra of Mn(II) complexes show four ab-
sorption bands at wavelength 17295–19476, 23530–24480,
27450–28500, and 34125–37120 cm−1. These bands may be as-
4
4
signed to the 6A1g → T1g (4G), 6A1g → Eg, 4A1g (4G), 6A1g
→
4Eg (4D), and A1g
→
4T1g (P) transitions, respectively.
6
The observed transitions suggest octahedral geometry for the
complexes.[20,21] The parameters like B and C (Racah parame-
ters), Dq, covalency factor β, LFSE, and F2 and F4 have been
calculated for the complexes. The value of the covalency factor
β being less than unity (0.44–0.74) suggests the partial covalent
character in the metal–ligand bonding.
EPR Spectra
The EPR spectral data of the complexes are presented in
Table 4. The X-band EPR spectra of Cr(III) complexes at room
H
H
N
N
C
N
C
N
X
H3C
CH3
Cr
X
H3C
N
N
CH3
X
O
O
N
N
(a)
H
H
N
N
C
C
X
H3C
N
N
CH3
Mn
X
H3C
N
N
CH3
O
O
N
N
(b)
FIG. 7. Fungicidal screening against A. brassicae of: (A) ligand, (B)
[Cr(L)(NO3)2]NO3, and (C) [Mn(L)Cl2] (color figure available online).
FIG. 6. Structure of the complexes: (a) [Cr(L)X2]X, (b) [Mn(L)X2], where
X = NO3−, Cl−, and CH3COO−.

STRUCTURAL AND PHARMACOLOGICAL STUDIES
931
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Pharmacological Studies
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Thesynthesis andmycological investigationsofanovelmetal
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