“ Synthesis and spectral studies of mixed ligand complexes of Fe(III) with benzoylacetone and salicylaldehyde, substituted salicylaldehydes, 2-hydroxy-aryl carbonyl compounds or β-diketones”
MITHLESH AGRAWAL*, GOPAL LAL YADAV and ANSHU KHANDELWAL,
*Asst.
Prof. Department of Chemistry, University
of Rajasthan , Jaipur-302004, India
ABSTRACT
Mixed ligand complexes of Fe(III) of the type and [Fe(bzac)2L], where bzac is benzoylacetone and HL is substituted salicylaldehyde, β-Diketones or hydroxylaryl ketones have been synthesized by the condensation reactions of Iron (III) chloride with a mixture of two different ligands in 1:2:1 molar ratios. The solid complexes were separated, filtered, washed with ethanol and ether successively and dried under reduced pressure. The resulting complexes have been characterized by elemental analyses, molar conductances, magnetic moments, electronic spectra, IR spectra and FAB mass spectra analysis. At the same time, above mentioned complexes were studied for in vitro antimicrobial properties and found to be more potent bactericides than parent ligands. Octahedral geometry has been proposed for the mixed ligand complexes.
Keywords: Mixed ligand complexes, Iron (III) chloride, IR spectra, FAB mass spectra, octahedral geometry, antimicrobial properties.
Introduction
:
Mixed ligand complexes play important roles in
biological processes like activation of enzymes by metals1,2. Such
complexes are useful in the storage and transport of active substances through
membrances3-5. Mixed ligand complexes have been used in the analysis
of semiconductor material. Semicarbazones constitute one of the most important
class of oxygen and nitrogen donar ligands6,7. Iron is essential to
nearly all known organisms. In cells, Iron is generally stored in the centre of
metalloproteins because “Free” ions (which bind non- specifically to many
cellular components) can catalyze production of toxic free radicals. Iron
deficiency can lead to iron deficiency anemia. In animals and plants, iron is
often the metal ion incorporated into the heme complex. Heme is an essential
component of cytochrome, protein, which mediate redox reactions, and of oxygen
carrier proteins such as hemoglobin, myoglobin and leghemoglobin. Iron
distribution is heavily regulated in mammals, partly because iron has a high
potential for biological toxicity8. Few mixed ligand complexes of
Fe(III) with β -diketones and nitrogen or phosphorus
containing ligands have been reported9-11.reaction mixture was kept on room temperature. The ppt was settled down. Filter the solution, washed with ethanol and dried properly under reduced pressure. (Scheme-1)
reaction mixture was kept on room temperature. The ppt was settled down. Filter the solution, washed with ethanol and dried properly under reduced pressure. (Scheme-1)
Antibacterial screening: The in
vitro antibacterial activities of the ligands and metal complexes were
tested by using Muller Hinton agar by well diffusion method21
against a gram negative bacterial strain Escherichia
coli (ATCC 25922). The bacterial strains grown on nutrient agar at 37ºC for 18 hours were suspended in a saline solution
(0.85% NaCl) and adjusted to a turbidity of 0.5 McFarland standards [108 colony forming
units (CFU)/ml]. The suspension was used to inoculate 90 mm diameter Petri
plates. Wells (6 mm diameter) were punched in the agar with the help of a
sterile metallic borer and filled with 100 µl of the test extract of the
concentration 5 mg/mL. The
dissolution of the organic extracts (Methanol) was reaction mixture was kept on room temperature. The ppt was settled down. Filter the solution, washed with ethanol and dried properly under reduced pressure. (Scheme-1)
Synthesis of mixed ligand complexes of Fe(III) with
benzoylacetone and substituted salicylaldehydes:-
To an ethanolic solution (~10 ml) of FeCl3
(5.24 mmol, 0.851g), an ethanolic solution (~10 ml) of benzoylacetone (10.48 mmol, 1.701g) and 5-bromosalicyaldehyde (5.24 mmol, 1.055g) were added with constant
stirring. The reaction mixture was
stirred for about 30-40 minutes. No ppt was obtained. Then, added 5% aqueous
sodium hydroxide solution (~7 ml) drop wise to the above reaction mixture to
raise the pH upto ~6.0. Stirred the solution for 3-4 hrs and then reflux the reaction mixture was kept on room temperature. The ppt was settled down. Filter the solution, washed with ethanol and dried properly under reduced pressure. (Scheme-1)
Where, X=Br and Cl
Scheme-1
Similarly,
the Mixed Ligand Complex of the type [Fe(bzac)2(5-Clsal)] was
synthesized by the reaction of FeCl3 with benzoylacetone and
5-chlorosalicylaldehyde.
(a) synthesis of mixed
ligand complexes of Fe(III) with benzoylacetone and β-diketones:-To
an ethanolic solution (~10 ml) of FeCl3 (4.35 mmol, 0.706g), an
ethanolic solution (~10 ml) of benzoylacetone
(8.70 mmol, 1.412g) and dibenzoylmethan
(4.35 mmol, 0.976g) were added with constant stirring. The reaction mixture was stirred for about 20-30 minutes. To attain the desired pH
(~5.0), 5% aqueous sodium hydroxide solution (~6-7 ml) was added with constant
stirring. Stirred the solution for 1-2 hrs and then reflux the reaction on
heating mental for 5-6 hour, the ppt began appear. After refluxing, the
reaction mixture was kept on room temperature. The ppt was settled down. Filter
the solution, washed with ethanol and dried properly under reduced pressure.
(Scheme-2)
Scheme-2
(c) Synthesis of mixed
ligand complexes of Fe(III) with benzoylacetone and hydroxyarylketones:-To
an ethanolic solution (~10 ml) of FeCl3 (9.80 mmol, 1.591g), an
ethanolic solution (~10 ml) of benzoylacetone
(19.8 mmol, 3.182g) and salicylaldehyde (9.80 mmol, 1.197g) were added with
constant stirring. The reaction mixture
was stirred for about 40-50 minutes. No ppt was obtained. Then, 5% aqueous
sodium hydroxide solution (~6-7 ml) was added drop wise to the above reaction
mixture to raise the pH upto ~5. Stirred the solution for 2-3 hrs. The reaction
mixture was reflex on heating mental for 5-6 hours the ppt began appear. After
refluxing, the reaction mixture was kept on room temperature. The ppt was
settled down. Filter the solution, washed with ethanol and dried properly under
reduced pressure. (Scheme-3)
Where, R1 R2
H H salicylaldehyde
CH3 H
2-hydroxyacetophenone
C2H5 H 2-hydroxypropiophenone
C6H5
H 2-hydroxybenzophenone
Scheme-3
Similarly,
the Mixed Ligand Complexes of the type [Fe(bzac)2(hap)], [Fe(bzac)2(hpp)] and [Fe(bzac)2(hbp)] were
synthesized by the reaction of FeCl3
with benzoylacetone and 2-hydroxy acetophenone,
2-hydroxypropiophenone or 2-hydroxybenzophenone.
RESULTS AND DISCUSSION
Analytical
and Physical measurements of synthesized complexes
The resulting mixed ligand complexes are obtained in 32-57% yields as
reddish brown or black brown solid. The data of C, H and Fe analyses agree well
with the calculated values corresponding to the respective complexes. The
complexes decomposed at high temperature on heating. All the physical data are
shown in Table 1. These are insoluble in water or most of the organic solvents
like methanol, benzene and carbon tetrachloride but soluble in DMSO and DMF.
Molar conductances: Molar
conductances (Λm) of 10-3 solutions of the complexes in
DMSO lie in very low range 4.5-10.9 Ω-1cm2mol-1
supporting their non-electrolytic behaviour22.
Magnetic
moments:
The
µeff values for the complexes are observed in the range 5.10 to 5.89
B.M. as expected for five unpaired electrons. . According to the μeff value
of these complexes the metal present in d5 electronic
configuration. Thus, all the complexes are high spin paramagnetic complexes23.
It lies within the octahedral range which is very close to spin value 5.90 B.M.
as the ground term is 6A1g and thus supports the
octahedral geometry.
Infra-red spectra: In free salicylaldehyde, 5-bromosalicylaldehyde, , benzoylacetone, dibenzoylmethane, 2-hydroxyacetophenone, 2-hydroxypropiophenone, 2-hydroxybenzophenone, 2-hydroxy-1-naphthaldehyde, bands appeared at 1680, 1670, 1650, 1640, 1650, 1724, 1724 and 1806cm–1 respectively have been assigned due to v(C=O)20,21. IR spectrum of [Fe(bzac)2(dbzm)] is reproduced in Fig. 1 A negative shift of this band to a value 1660-1625cm–1 in the complexes, is consistent with the coordination of the carbonyl oxygen of the ligands to the central metal ion. In the IR spectra of Fe (III) mixed ligand complexes, strong absorption bands in the region 1556-1512 cm-1 may be attributed to coordinated to ν(C=C). Weak absorption bands in the region 490-410 cm-1, which are absent in the free ligands, may be attributed to ν(Fe-O) vibrations. Bellamy and Beecher20 initially attributed the 1580 and 1520 Cm-1 bands to C=O and C=C stretching respectively. The assignments were reversed by Nakamoto et al21on the basis of force constant calculations. Mikami et al24supported the later view although the two modes were shown to be coupled slightly with each other.
Electronic spectra: The electronic spectra of Fe(III) complexes exhibit three bands. An intense band at 300-350 nm with high value may be assigned to intra-ligand transition. Another intense band at 350-400 is due to t2g transition (metal to ligand charge transfer). Band at 450-500 nm may be assigned to eg transition (ligand to metal charge transfer). UV-VIS spectrum of [Fe(bzac)2(dbzm)] is reproduced in Fig.2. In tris(β-diketonates) of Fe(III) Lintvedt and Kernitsky25 have assigned the bands at 270-340, 340-420 and 430-500 nm to intra-ligand transitions, t2g metal to ligand charge transfer transitions and eg ligand to metal charge transfer respectively.
FAB mass spectra:-. FAB mass spectra of three complexes
[Fe(bzac)2(hap)] (I), [Fe(bzac)2(hpp) (II) and [Fe(bzac)2(dbzm)]
(III) have been recorded and the m/z values of the peaks along with their
intensities relative to the base peak are given in Table 2. Mass spectrum of
[Fe(bzac)2(dbzm)] is reproduced in Fig. 3. Peaks at m/z 199, 200,
217, 342 and 370 are due to NBA matrix. All the complexes exhibit molecular ion
(M+) peaks of very low intensity (I, m/z 513, 1.4%, II, m/z 527, 1.4%
and III, m/z 601, 2.8%). Sasaki and coworkers26 have studied the
mass spectra of various metal acetylacetonates and have observed that for the
central metal atoms having electronegativities between 1.6-1.8, molecular ion
peak was of very low intensity or was not observed. The peaks at m/z 380 due to
Fe(bzac)2+ which is formed by the loss of the other
ligand moiety (L) from the molecular ion (M+) in the complexes I and
II and at m/z 502 due to Fe(dbzm)2+ in the complex III
are the base peaks (100%). In the complex III, the peak due to Fe(bzac)2+
is of 30.5% intensity. In the mass spectra of Fe(III) acetylacetonates or
substituted acetylacetonates the base peaks due to Fe(acac)2+
have been reported27,28.
Loss
of benzoylacetone moiety from Fe(bzac)2+ gives Fe(bzac)+
which exhibits quite intense peak at m/z 218 ( I, 44.4%, II, 61.1%, III,
19.4%). Removal of benzoylacetone moiety from the molecular ion (M+)
results in the formation of Fe(bzac)L+ which gives less intense peak
in complexes (I) (m/z 353, 2.8%) and II (m/z 367, 2.8%) while very intense peak
is observed in the complex (III) (m/z 441, 94.4%). Further loss of another
benzoylacetone moiety gives the species FeL+ which again exhibits
less intense peak in complexes (I) (m/z 191, 1.4%) and II (m/z 205, 1.4%)
whereas the peak in the complex (III) is quite intense (m/z 279, 41.6%).
|
|
|
Path-II
Fe(bzac)2L+
Fe(bzac)L+ FeL+
Complex (III) exhibits the base peak (100% intensity) at m/z 502 due to the species Fe(dbzm)2+. Similar species [Fe(hap)2]+ in case of complex (I) also gives a strong peak at (m/z 326, 58.3%) whereas complex (II) does not show any peak due to the corresponding species. Less intense peaks due to the species Fe(bzac)L2+ are observed in case of complexes (I) and (III). Such species might have been formed as a result of the following reactions.
FeL+
+ L FeL2+
FeL2+ +
bzac Fe(bzac)L2+
Table 2- Mass spectral data of mixed ligand complexes of Fe(III) (m/z values and relative abundances)
L = hap,
hpp or dbzm
Biological activity of
the synthesized complexes:-The synthesized complexes were screened for
antimicrobial activity. Antimicrobial activities were carried out using paper
disc method against gram negative bacteria. Two of the ligands named 2-hydroxyacetophenone
& 2-hydroxy benzophenone and three of the newly prepared corresponding mixed
ligand complexes of Iron [Fe(bzac)2 (hap)], [Fe(bzac)2
(hbp)] and [Fe(bzac)2 (5-Brsal)] were screened in vitro for their antibacterial activity against gram
negative bacteria Escherichia Coli (MTCC 29213) using Nutrient Agar by disc
diffusion method. The bacterial strains grown on Nutrient Agar at 37 C for 18
hours were suspended in peptone water (1%). The suspension was used to
inoculate 90 mm diameter Petri plates.
Discs (6 mm diameter) were prepared from Whatman No.
1 filter paper. Samples and standard (Ciprofloxacin) solutions were prepared in
DMSO. The discs were dipped into sample and placed on to the agar with the help
of sterile forceps. The dissolution of the organic extracts was aided by DMSO,
which did not affect the growth of microorganism in accordance with control
experiments, behaved as negative control. The plates were incubated in
incubator at 37°C for 24
hours. Antibacterial activities were evaluated by measuring inhibition zone
diameters.
The
free ligands and their metal complexes were tested against the bacterial
species. Ciprofloxacin as a standard antibacterial agent or reference was
evaluated for their antibacterial activity and the results were compared with
the free ligands and their metal complexes. The comparison of the biological
activities of the synthesized complexes and known antibiotic shown the
following results-
1.
The prepared
metal complexes show positive effect towards Escherichia Coli strains while
ligands do not show activity towards Escherichia Coli strains.
2.
The complexes
are more potent bactericidal against Escherichia Coli than standard.
3.
The
antibacterial screening data shows that the prepared metal complexes exhibit
more inhibitory effects than the parent ligands. From the Table-3, it is clear
that the zone of inhibition (bacteriostatic diameter) is much larger for metal
complexes for bacterial strains.
Table3. Antibacterial activities of
the ligands and Iron metal complexes
Conclusion:-
In the light of the above discussion, an octahedral geometry for Fe(III)
complexes are proposed. All the complexes are non-electrolyte and high spin
paramagnetic in nature. Magnetic moments and electronic spectra confirm an
octahedral geometry of the complexes.
In the IR spectra of the complexes, shifting of ν(C=O) to lower wave number
side supports the chelation of the ligand to the metal atom and also support
the absence of coordinated water molecules in the complexes. Mass spectral
study further confirms the proposed structure of the complexes. The complexes
are biologically active and exhibit enhanced antibacterial activities as
compared to their parent ligands, hence further study of these complexes could
lead to interesting results
Acknowledgements:
The
authors are thankful to the Head, Department of Chemistry, University of
Rajasthan, Jaipur for laboratory facilities, Department of Chemistry, Banasthali Vidyapith, Banasthali, Rajasthan for
magnetic moments, the Director, CDRI, Lucknow for C, H analyses and FAB
mass spectra, Ground Water Department, Jaipur, Rajasthan for electronic
spectra, and the Principal, Dr. B. Lal Institute of Biotechnology, Jaipur for
antibacterial screening.
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