Synthesis and Structural Studies of Cr(III), Mn(II) and Fe ...
Transcript of Synthesis and Structural Studies of Cr(III), Mn(II) and Fe ...
ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.e-journals.net 2011, 8(1), 421-426
Synthesis and Structural Studies of
Cr(III), Mn(II) and Fe(III) Complexes of
N(2-Benzimidazolyl)acetylacetohydrazone
G. H. ANURADHA* and A.V. CHANDRA PAL
*Department of Chemistry
R.B.V.R.R Women’s College, Hyderabad- 500027, India
Department of Chemistry
Osmania University, Hyderabad-500007, India
Received 9 February 2010; Revised 25 June 2010; Accepted 17 July 2010
Abstract: The ligand N(2-benzimidazolyl)acetylacetohydrazone (BAAH) have
been synthesized and characterized. Coordination complexes of Cr(III), Mn(II)
and Fe(III) have been synthesized with the ligand BAAH. These complexes
were characterized on the basis of analytical, conductance, thermal, magnetic
data and infrared and electronic spectral data. The ligand BAAH is behaving as
a neutral tridentate NNO donar employing two azomethine nitrogens (ring and
side chain) and carbonyl oxygen. The ligand and it’s metal complexes were
tested for anti microbial activity on the gram positive S. Aureus, E. coli
and Proteus.
Keywords: BAAH, Metal complexes, Physiological activity.
Introduction
The chemistry of benzimidazole and it’s derivatives reported in the literature is interesting
due to their chelating ability and physiological properties such as antiviral, fungicidal,
bactericidal in addition to analytical applications1,2
. 2-Hydrazinobenzimidazole have been
proved to be very active against the transition metal ions3-5
. Some derivatives of
2-substituted benzimidazoles show anti microbial6, anti influenza
7 and hypertensive
activities8. In view of this it was planned to make a study on the complexing abilities of
compounds (Schiff bases) derived from 2-hydrazinobenzimidazole with acetylacetone and
their antimicrobial activity also tested.
Experimental
Metal salts and solvents used were E-Merk products. All other chemicals used were of AR
grade. Elemental analysis (C, H. & N) was carried out using micro analytical techniques on
422 G. H. ANURADHA et al.
Heraens -CHN rapid analyzer. Metal estimations were done on a Perkin Elmer 2380 atomic
absorption spectrometer, conductivity measurements were carried on Elico digital
conductivity meter model No. CM-180, the magnetic susceptibility measurements were done
on a Faraday balance (CAHN-7600) using HgCo(SCN)4 as standard. DTA data was
established by using leeds and Northrup – USA instrument. Infrared spectra were recorded
on a Perkin - Elmer 1600. Fourier transforms infrared spectrophotometer in nujol mull. The
electronic spectra were recorded on a shimdazu UV - 160 spectrophotometer.
Synthesis of ligand (BAAH)
Acetylacetone (1.2 mL) was added to a solution of 2-hydrazinobenzimidazole (1.48 g) in
methanol (100 mL). The mixture was heated under reflux for three hours and then poured
into ice cold water. The white needles separated out were filtered and washed with a small
amount of aqueous alcohol. The compound was dried in vacuo and recrystallized from
aqueous methanol. Yield 60% m.p. 130 0C.
Characterization of the ligand
The molecular formula of the ligand is C12H14N4O. The 1H NMR spectrum of BAAH was
recorded in DMSO-d6 solution. The spectrum revealed surprisingly only two methyl
signals9, one at δ 6 characteristic of an olefinic proton and a broad peak at δ 10.6 reminiscent
of an intra molecular bonded enolic OH appeared10
. The usual A2B2 pattern of the aromatic
protons in 2-hydrazinobenzimidazole is also absent. All the information conforms to the
enol tautomeric structure of the compound.
The IR spectrum of BAAH shows a peak at 3060 cm-1
assigned11
to stretching vibration
of free νN-H. A band due to ring νN-H vibration is observed at 2923 cm-1
. Two sharp bands
observed at 1626 and 1551 cm-1
are ascribed to free νC=N and ring νC=N respectively12
.
The νN-N stretching frequency is observed13
at 1033 cm-1
. Surprisingly νC=O is not
observed, this confirms enol tautomerism.
The highest ion peak in the mass spectrum of the compound BAAH is at m/e 212.
Obviously the molecule looses elements of water under thermal conditions and hence the
molecular ion is not recorded. The ion at m/e 212 is also the base peak in the spectrum and is
represented by 2-pyrazolylbenzimidazole derivative. The molecular ion and the ion at m/e
212 appears to undergo extensive skeletal rearrangements giving ions at m/e 195, 184, 170,
144 and 133. The peak at m/e 133 corresponds to 2-aminobenzimidazole. The next
prominent amongst the ions is m/e 118 corresponding to benzimidazole and m/e 105
corresponding to benzazetidine moiety.
The electronic spectrum of BAAH ligand shows absorptions at 42918 cm-1,
33333 cm-1
,
26737 cm-1, 23355 cm
-1 and 21978 cm
-1. The high energy band 42918 cm
-1 is attributed to Π → Π*
transition of benzimidazole. The band at 33333 cm-1 is attributed to benzene moiety. The other
bands are assigned to the transitions possible with carbonyl group and azomethine groups.
The data are consistent with the expected structure (Figure 1) and confirms the enol
tautomeric structure of the compound.
N
N
N H N = C --- C H = C ---- CH 3
lOH
lCH3
H Figure 1. N(2-Benzimidazolyl)acetylacetohydrazone
Synthesis and Structural Studies of Cr(III), Mn(II) and Fe(III) Complexes 423
Synthesis of metal complexes
The ligand (0.01 mole) was dissolved in methanol (25 mL.) and to this solution of divalent /
trivalent metal chloride (0.01 mole) was added. The pH of the mixture was adjusted to 7
with 1% alcoholic ammonia and the reaction mixture was refluxed for 3-4 h. The coloured
product thus obtained was filtered in hot condition, washed successively with methanol and
petroleum ether and dried in vacuo. The purity of complexes was checked by TLC using
methanol and solvent mixtures.
Results and Discussion
Characterization of the metal complexes
Analytical data of C,H,N,Cl and metal are in good agreement with 1:1 (Table 1) metal-
ligand stoichiometry for all the three complexes. All the complexes are coloured and
stable, they neither melt nor decompose up to 300 0C. Except Cr(III) complex the
remaining two Mn(II) and Fe(III) complexes show negligible conductivity thus proving
that they are non- electrolytes. The conductance value of Cr(III) is 60 mhos indicating to
be 1:1 electrolyte. Hence one chloride ion is present in the ionization sphere of Cr(III)
complex. The differential thermal analysis of BAAH Cr(III) complex indicates that it
undergoes thermal decomposition in the range of 60 0C to 540
0C. There is a broad
endotherm in the range of 60 0C to 300
0C which is attributed to the deaquation of both
lattice water and coordinated water14,15
.
Table 1. Analytical data of complexes of BAAH
Calculated (Found) % ΩM Complex
stochiometry Carbon Hydrogen Nitrogen Chloride Metal mho cm
2
mol-1
Cr(III) complex
(CrC12H20N4O4Cl3)
33.91
(33.89)
4.24
(4.22)
13.18
(13.15)
25.08
(25.07)
12.24
(12.20) 60
Mn(II) complex
(MnC12H18N4O4)
42.72
(42.68)
5.34
(5.30)
16.61
(16.59) -
16.31
(16.25) 15
Fe(III) complex
(FeC12H17N4O4)
42.72
(42.70)
5.04
(5.01)
16.61
(16.58) -
16.61
(16.56) 24
Where L = C12H14N4O
Infrared spectra
The IR spectral data of the BAAH complexes are given in Table 2. The ligand seems to
employ the keto form in metal binding process. The strong band observed in the range of
1600-1620 cm-1
is due to νC=0 which is characteristic of keto form. In view of its
appearance at relatively low frequency it can be concluded that the carbonyl function is
involved in coordination. Below 1600 cm-1
the spectra of the complexes are more elaborate.
Invariably there is a sharp band around 1560 cm-1
and another similar band in the range of
1523 cm-1
. These bands are assigned to νC=N free and νC=N ring respectively which are
involved in coordination16,17
. Based on these observations it may be concluded that the
BAAH is behaving as a neutral tridentate NNO donar.
The νN-N appearing at 1033 cm-1
in free ligand spectra is located at a higher frequency
(up to 1060 cm-1
) in the spectra of all the complexes18
. It further supports the involvement of
azomethine nitrogen of hydrazine side chain in coordination. The peak at 740 cm-1
which is
assigned to the N-H out of plane deformation vibration in free ligand is not altered on
chelation, since coordination does not take place through the imino nitrogen atom.
424 G. H. ANURADHA et al.
Table 2. Characteristic IR frequencies of BAAH metal complexes
Complex νOH
νNH νC=O
νC=N
(free)
νC=N
(ring) νN-N New bands
BAAH 3060-
2924 - 1626 1552 1033
Cr(III)
complex
3000-
3400 1608 1560 1522 1060
920, 670, 565,
524, 480, 300, 270
Mn(II)
complex
3200-
3420 1600 1578 1523 1045
1119, 620, 502,
485, 390, 320
Fe(III)
complex
3100-
3365 1620 1560 1523 1043 1121, 567, 532
The position of broad bands in the spectra of the complexes at higher frequencies in
comparison with the band in the free ligand (2424 - 3060 cm-1
) can be attributed to νOH
of either hydroxide or water molecules. The spectra of metal complexes show a broad
strong band in the region 3000 to 3450 cm-1
which can be attributed19
to νNH and νOH.
In Mn(II) and Fe(III) complexes the presence of hydroxyl ions in coordination is further
supported by non ligand bands in the range of 1110-1121 cm-1
which are due to M-OH
bending modes.
The presence of coordinated water in Mn(III) complex is concluded by rocking and
wagging modes observed in the range of 880 - 930 cm-1
and 670 - 650 cm-1
respectively20
.
In the far IR spectra of Cr(III) complex non ligand bands at 270-300 cm-1
which are assigned
to coordinated chloride ions. The non ligand bands in the range of 485 - 670 cm-1
in all the
complexes are assigned to νM-O and νM-N vibrations21
.
Magnetic data
Magnetic susceptibilities are recorded at room temperature on faraday balance and the
magnetic moments (BM) calculated show that central metal ions are invariably in high spin
configurations. The magnetic moments were presented in Table 3. The magnetic moment of
Cr(III) complex is 3.82 BM which corresponds to a d3 system. The magnetic moment values
of Mn(II) complex is 6.1 BM, which is to be expected for d5 system
22. The Fe(III) complex
has a magnetic moment value of 5.9 BM, which corresponds to high spin d5 configuration
23.
Electronic spectra
The electronic spectral data of the complexes are given in Table 3. The absorption spectra of
Cr(III) complex exhibit three bands at 12,345 19,047 and 33,333 cm-1
. These are assigned in
sequence to 4A2 →
4T2,
4A2 →
4T1 (F) and
4A2 →
4T1 (P) transitions respectively. Octahedral
geometry is proposed24
. The absorption spectra of Mn(II) complex show bands at 19,047,
21,505, 23752 and 26,737 cm-1
. These bands can be attributed to doubly forbidden
transitions25
. The absorption spectrum of Fe(III) complex exhibits weak absorptions at
38,461, 12,453 and 11,614 cm-1
and can not be assigned to specific transitions.
Table 3. Magnetic and Electronic spectral data of BAAH metal complexes
Complex µeff (BM) Electronic spectral bands, cm-1
Cr(III) complex 3.82 12345, 19047, 33333
Mn(II) complex 6.1 19047, 21505, 23752, 26737
Fe(III) complex 5.9 11614, 12453, 38461
Synthesis and Structural Studies of Cr(III), Mn(II) and Fe(III) Complexes 425
Physiological activity
The culture was prepared by the addition of 1.5 g of Beef extract, 1.5 g of yeast extract,
5.0 g of peptone, 1.0 g dextrose, 3.5 g of NaCl, 3.68 g of dipotassium hydrogen phosphate,
1.32 g of mono potassium dihydrogen phosphate and 15 g of agar agar in one litre of water.
The pH of the medium was adjusted to 7.0. The medium was sterilized at 121 0C in an
autoclave at 15 lbs pressure for 15-20 minutes. The medium was cooled to 45-50 0C. 20 mL of
medium was poured in each of the Petri dishes. All the apparatus used were sterilized.
E.coli, S. aureus and proteus were introduced into the Petri plates and were grown.
Bacteriological testing
Bacteriological testing was done using paper disc method. Paper discs were soaked in the
solutions of ligand and complexes in DMF. Solutions were prepared in 100 µg/mL in DMF.
Paper discs were soaked in this solution and were dried. The dried paper discs were
introduced into the fully grown culture plates of E.Coli, S. aureus and Proteus.
The ligand BAAH is active against E.coli and inactive against S.aureus and Proteus.
Cr(III) complex is active against E.coli, S. aureus and Proteus. Mn(II) and Fe(III)
complexes are active against E.coli and S. aureus and inactive against Proteus.
Conclusion
BAAH is behaving as a neutral tridentate NNO system employing two azomethine nitrogens
(ring and side chain) and carbonyl oxygen. All the complexes are homonuclear and forming
1:1 complexes. From IR spectra it is suggested that ligand seems to employ the keto form in
metal binding process. Based on analytical, thermal, conductivity, magnetic and spectral
data octahedral geometries have been proposed to Cr(III), Mn(II) and Fe(III). The proposed
structures are given in Figure 2.
Figure 2. Probable structures of Cr(III), Mn(II) and Fe(III) complexes of the ligand BAAH
426 G. H. ANURADHA et al.
Acknowledgment
The authors are thankful to NCL Pune, Department of Chemistry, Pune University, CIL,
Hyderabad University and IICT, Hyderabad for providing spectral and library facilities.
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