Synthesis, characterization and biological evaluation of transition and inner transition metal complexes of ligands derived Schiff base from 1-phenyl-2, 3-dimethyl-4-(4-iminopentan-2-one)-pyrazole-5-one and 2-aminophenol

Article abstract of DOI:10.13005/ojc/290228

The ligand derived from 1-phenyl-2, 3-dimethyl-4-(4-iminopentan-2-one)- pyrazolin-5-one and 2-aminophenol behaved in neutral tetra dentate manner. Its complexes with Ti (III), V (III), Mn (III), Ru (III), MoO (V), MoO₂ (VI), and UO₂

Full text of DOI:10.13005/ojc/290228

ISSN: 0970-020 X
CODEN: OJCHEG
2013, Vol. 29, No. (2):
Pg. 589-595
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Est. 1984
Synthesis, Characterization and Biological Evaluation of
Transition and Inner Transition Metal Complexes of Ligands
Derived Schiff Base from 1-phenyl-2, 3-dimethyl-4-(4-
iminopentan-2-one)-pyrazole-5-one and 2-aminophenol
ANUBHA SAXENAand RAJNEESH SAXENA
1Department of Chemistry, S.M. College, Station Road, Chandausi - 202 412, India.
(Received: March 19, 2013; Accepted: May 03, 2013)
ABSTRACT
The ligand derived from 1-phenyl-2, 3-dimethyl-4-(4-iminopentan-2-one)-pyrazolin-5-one
and 2-aminophenol behaved in neutral tetra dentate manner. Its complexes with Ti (III), V (III), Mn
(III), Ru (III), MoO (V), MoO2 (VI), and UO2 (VI) were prepared and characterized by elemental
analysis, conductivity, magnetic studies and spectral data. Based on these studies octahedral
geometry has been proposed for all these complexes. The ligand and selected transition metal
complexes have also been evaluated for antimicrobial activity against S. aureus and B. subtilis.
From the biological data, we can infer that Schiff base of 4-aminoantipyrin has better antimicrobial
activity in comparison to the native one. Also, the antimicrobial activity is highly influenced by the
nature of the metal ion. The order of antibacterial activities against S. aureus and B. subtilis are
MoO (V) > MoO2 (VI) > UO2 (VI) H” Ru (III) > Mn (III) > V (III) > Ti (III) and Mn (III) > MoO (V) > MoO2
(VI) > Ru (III) > UO2 (VI) > V (III) > Ti (III) respectively.
Key words: Schiff base, transition metal complex, ligand, antimicrobial and octahedral.
INTRODUCTION
important biological reactions and mimic the
catalytic activities of metalloenzymes3-4. Recently,
the Schiff bases ligand containing various donor
atoms (like N, O, S etc.) and their metal complexes
have been shown broad range of their application
as biological, biochemical, analytical, antimicrobial,
antibacterial, anticancer, antitumor and antifungal
activity5-9. They used as catalyst, in medicine like
antibiotics and anti-inflammatory agents and in the
industry as anticorrosion.The synthesis of transition
The term Schiff base was
invented by Hugo Schiff for the condensation
reaction between an aldehyde and an amine. Schiff
base ligands are able to coordinate metals through
imine nitrogen and another group usually linked to
aldehyde or ketone1,2. Schiff base complexes
incorporating phenolic group as chelating moieties
in the ligand are considered as models for executing

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SAXENA & SAXENA, Orient. J. Chem., Vol. 29(2), 589-595 (2013)
metal complexes with Schiff base ligands are gravimetric estimation method. The elemental
considered due to sensitivity, selectivity and synthetic analysis was carried out at CDRI, Lucknow.
flexibility towards metal atoms10. It is known that the
existence of metal ions bonded to biologically active Preparation of Schiff base ligand
compounds may increase their activities11-14. In
2-aminophenol (1.09 g, 10 mmol) was
recent years, because of new interesting added to the solution of 1-phenyl-2, 3-dimethyl-4-
applications found in the field of medicine, the metal (4-iminopentan-2-one)-pyrazol-5-one (2.85 g, 10
complexes with tridentate O, N, N types of alternative mmol) in 50 ml of ethanol.The reaction mixture was
structures have attracted the attention of chemist. In refluxed for 10 h. On cooling, the orange solid was
this paper we describe the synthesis, filtered and recrystallized from ethanol in 90% yield.
characterization and behavior of the tetradentate The purity of the sample was checked by TLC. The
Schiff bases of 4-aminoantipyrin ligands with ligand was characterized by the determination of
various metal complexes.The structures of all these melting point (146 °C), elemental analysis and IR
complexes have been investigated by using spectra.
elemental analysis, FTIR, elemental analysis,
magnetic susceptibility and conductivity Preparation of transition metal complexes
measurements. Although 4-aminoantipyrin itself
The solution of the metal salt was added
exhibits antimicrobial activity, its activity can be drop wise to the solution of the ligand 3 with constant
enhanced by formation of its Schiff’s bases by stirring till the complete precipitation occurred. The
condensation with aldehydes, ketones, carbazides precipitation was filtered, washed. The obtained
etc. Antibacterial activities of these complexes were product was washed with ether and dried over
determined as MICs values using the micro dilution vacuum desiccator. The yields of the purified
broth method against gram-positive bacteria, complexes are varying from 55-70%. The reaction
Staphylococcus aureus and Bacillus subtilis.
scheme is shown in Figure 1 and analytical and
physical data are shown in Table 1.
MATERIAL AND METHODS
Antibacterial activity
Physical measurement
Antibacterial activity was tested against
All the chemicals and solvents used were Gram +ve (Staphylococcus aureus and Bacillus
of highest purity or A.R. grade.The metal salts used subtilis) by the disc diffusion method using agar
wereTiCl3, VCl3 MnCl3, RuCl3, MoOCl3, MoO2Cl2 and nutrient as medium and utilizing silver nitrate as
UO2 (NO3)2.TiCl3 was prepared in the lab by literature control. The disc susceptibility test16-18 is a relatively
method while all other metal salts were procured robust and simple technique for determining the
from Merck and used as such. The solvents were sensitivity profiles of Staphylococcus aureus and
carefully purified before use. Melting points of the Bacillus subtilis.However, many factors such as agar
ligand and its metal complexes were determined in source, inoculum size, disc potency, incubation
an Electro thermal 9200 by open capillary method. temperature and length of incubation can influence
The IR spectra (Nujol/KBr) were recorded in the zone size diameter19-20. Plate inoculation methods
range 400- 4000 cm-1 by KBr pellet using Perkin- have included streaking and a combination of both
Elmer 457 spectrophotometer at CDRI, Lucknow. streaking and flooding. In this study both methods
The molar conductance was measured with digital of plate flooding and streaking gave reproducible
conductivity meter (HPG system G-3001) using a results within each technique and were equally
Digital conductivity bridge in DMF and DMSO at 10- practical. The stock solutions were prepared in
3
M dilution at room temperature. Magnetic acetonitrile for each of the compound and all blank
susceptibility was determined by Gouy’s balance discs were moisturized with the solvent. Paper
[13] using CuSO4.5H2O as calibrant. The electronic containing the compounds were placed on the
spectra of the complexes were recorded by surface of the nutrient agar plates previously spread
Beckmann-DU-Spectrophotometer (Fullerton, (streaking and flooding) with 0.1 ml of overnight
California 92834-3100, USA). The metal and cultures of micro-organisms. After 36 h of incubation
chloride contents were determined through at 37oC, the diameter of inhibition zones was

SAXENA & SAXENA, Orient. J. Chem., Vol. 29(2), 589-595 (2013)
591
measured.The % activity Index for the complex was
calculated by the formula as below:
MoO(V) complexes and non-electrolytic nature for
MoO2 (VI) and UO2 (VI) complexes. The magnetic
moment values at room temperature are consistent
with that of octahedral geometry around the central
metal ion (Table 1). The MoO2 (VI) and UO2 (VI)
complexes are diamagnetic in nature while all other
complexes are paramagnetic in character. Thermal
analysis shows that Ti (III), Mn (III), V (III), Ru (III)
complexes possess two coordinated water
molecules whereas MoO (V) complex has only one
coordinated water molecule.
RESULTS AND DISCUSSION
The analytical data suggested 1:1 (M:L)
stoichiometry for all the synthesized complexes as
shown in Table 1. The molar conductance
measurement of the complexes suggested 1:1
electrolytic nature for Ti (III), V (III), Mn (III), Ru (III),
IR spectra
Scheme 1: Synthesis of metal (Ti (III),V (III), Mn (III), Ru (III),
MoO (V), MoO2 (VI), and UO2 (VI)) complexes with Ligand

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SAXENA & SAXENA, Orient. J. Chem., Vol. 29(2), 589-595 (2013)
The IR spectrum of the ligand was 5Eg and Mn (dπ) → π* (azomethine) respectively.
compared with those of corresponding metal These bands are characteristic of octahedral
complexes in order to find out the possible geometry26.The Ru (III) complex demonstrates three
coordination sites. The ligand shows a weak broad band in its electronic spectrum at 13650 cm-1, 17600
band at 2950 cm-1 which has been assigned to cm-1 and 22500 cm--1, which may be assigned to
2
2
2
intramolecular hydrogen bonding between 2T2g
→ → →
4T1g, T2g 4T2g and T2g 2A2g, T1g
enolizable -C = O of pentan-2, 4-dione and phenolic respectively for octahedral symmetry27, 28.The V (III)
group21. This band has disappeared in all the metal complex shows a band at 16000 cm-1 with shoulder
complexes, which indicates the deprotonation of at 21000 cm-1. The low energy has been assigned
enolic and phenolic groups upon complexation. In to 3T1g → T2g whereas high energy band to 3T1g
→
3
addition to that, the absence of a band at 1660- 3T1g (P) transitions, characteristic of octahedral
1700 cm-1 (which is characteristic of free -C = O geometry around V (III) ion31. The electronic
group) suggests that the carbonyl group is in enolic spectrum of MoO (V) complex exhibits bands at
form.This has suggested dibasic nature of the ligand. 14200 cm-1, 19610 cm-1 and 25000 cm-1 assignable
The ligand shows a band at 1610 cm-1 characteristic to B2→ E (dxy→dxz, dyz), B2 → A (dxy→dx2-y2)
2
2
2
2
of -C = N (azomethine group).This band is shifted to and B2 → A2 (dxy → dz2) transitions respectively
a lower frequency by 20-25 cm-1 in all the metal and suggest octahedral environment around MO (V)
complexes. This indicates the involvement of ion32. The electronic spectra of MoO2 (VI) and UO2
nitrogen atom of azomethine group in coordination (VI) complexes show only charge–transfer
with the metal ion22. These coordination sites are transitions.
2
2
further confirmed by the presence of non-ligand
bands in the far IR region (430-490 cm-1 and 360- Antimicrobial activity
410 cm-1) of the complex due to VM-O and VM-N
The antibacterial activity of tetradentated
respectively23. All complexes, except MoO2 (VI) and aromatic Schiff base ligands and their metal
UO2 (VI) show broad band in the region of 3500- complexes were screened against microorganism.
5100cm-1 due to VO-H of water molecule. The The microorganisms used in the present
coordinated nature of the water molecule/molecules investigations include bacteria: Staphylococcus
is confirmed by two other non-ligand bands in the aureus and Bacillus subtilis. Minimum inhibitory
region of 840-855 cm-1 (wagging) and 740-750 cm- concentrations (MICs) method was used to
1
(rocking) modes of water molecules. TGA also determine the antibacterial activity of the
supported the coordinated nature of water synthesized compounds. The diffusion method is
molecules22. The MoO (V) complex shows another very simple, it requires moistened disks with the
non-ligand band at 950 cm-1 assignable to MO=O solution of Ligand metal complex, the medium used
stretching frequency.The MoO2 (VI) complex shows is Mueller-Hinton agar with 2% of glucose and the
bands at 960 and 910 cm-1 attributable to Vsym diameter of inhibition zone is visually read at 36
(O=MO=O) and Vsym (O=MO=O) respectively of Cis hours after incubation at 37°C. The antibacterial
MoO2 configuration25. The UO2 (VI) complex shows activity was estimated on the basis of the size of the
Vas (OUO) and Vs (OUO) modes at 885 and 790 inhibition zone formed around the paper disks on
cm-1 respectively, suggesting trans nature (O=U=O) the seeded agar plates (Figure 1).
of UO2 group26.
The results are presented in Table 2. A
Reflectance
measurements
spectra
and
magnetic comparative study of the ligands and their metal
complexes31,32 indicates that most of the metal
The electronic spectra of the metal chelates exhibit higher antimicrobial activity than
complexes also supported the octahedral geometry that of the free ligand and the control as shown in
for all these complexes.The Ti (III) complex shows a Table 2. This increased antimicrobial activity of the
2
2
broad band at 20110 cm-1 assign to T2g→ Eg metal chelates can be explained on the basis of
transition for octahedral symmetry [25]. The Mn (III) overtone’s concept35 and chelation theory36. The
complex shows three bands at 19000 cm-1, 13000 biological activity of the complexes follows the order:
5
cm-1 and 20,000 cm-1 assign to 5B1g → B2g, 5B1g
→
MoO (V) ≈ MoO2 (VI) > Mn (III) > Ru (III) ≈ UO2 (VI)

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Table 2: The antibacterial activity of the ligand
and its metal complexes (The data shown is mean
value of the three independent experiments)
Compound
S. aureus
B. subtilis
Control (Ag NO3), 11
Ligand, 3
+
+
++
+
[Ti L. 2H2O] Cl, 4
[VL. 2H2O] Cl, 5
[MnL.2H2O] Cl, 6
[RuL.2H2O] Cl, 7
[MoO.L.H2O] Cl, 8
[MoO2L], 9
++
++
++
+++
+++
+++
++++
++++
+++
++++
+++
++++
+++
+++
[UO2L], 10
C* = 4 µg/ml. Inhibition zone diameter mm (% inhibition) “+,
7-11 (32-50 %), ++11-15 (50-68 %), +++ 15-19 (68-86
%), ++++19-23 (86-100 %)
Fig. 1: Representative disk diffusion test plate
showing zone of inhibition on Staphylococcus
aureus inoculated plate of Ligand, Metal ligand
complex and control at the concentration of 4
µg/ml.The abbreviations Control (Ag NO3), 11,
Ligand, 3, [TiL. 2H2O] Cl, 4, [Mn L. 2H2O] Cl, 5,
[VL. 2H2O] Cl, 6, [RuL. 2H2O] Cl, 7, [MoOL. H2O]
Cl, 8, [MoO2L], 9, [UO2 L], 10
>Ti (III). Furthermore, the data shows that
Staphylococcus aureus was inhibited to a greater
degree by the MoO (V) and MoO2 (VI) complexes,
whereas Bacillus subtilis was inhibited to a greater
degree by Mn and MoO. In conclusion the
complexes prepared with the new Schiff base could (VI) and UO2 (VI) complexes are non-electrolytic in
be used for the treatment of some common diseases nature. Schiff base behaves as a neutral tetradentate
caused by Staphylococcus aureus and Bacillus ligand and is coordinated to the central metal ion.
subtilis.
On the basis of studies performed octahedral
geometry has been proposed for all the synthesized
complexes. The biological activity of all the
complexes is higher than free Schiff base ligand
CONCLUSION
Ti (III), Mn (III), V (III), Ru (III) and MoO (V) and follows the order: MoO (V) ≈ MoO2 (VI) > Mn (III)
complexes of the Schiff base derived from 1- > Ru (III) ≈ UO2 (VI) > Ti (III). This means that metal
phenyl-2,3-dimethyl-4-(4-iminopentan-2-one)- chelation significantly affects the antimicrobial
pyrazole-5-one and 2-aminophenol and behavior of the organic ligand.
complexes are electrolytic in nature, whereas MoO2
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