940 Bhale et al.
Asian J. Chem.
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disappearing in all metal complexes clearly indicates the parti-
cipation of pyranone oxygen in coordination with the metal
ions by deprotonation [21]. The strong band for azomethine
group at 1595 cm-1 in ligand was shifted to lower side in the
IR spectrum of all metal complexes, indicating the coordination
of azomethine nitrogen to metal ion. In free ligand band at
1662 cm-1 arises due to C=O stretch of pyranone ring in all metal
complexes which indicates its non-participation in coordi-
nation. Spectral data suggests that the ligand has coordinated
through azomethine nitrogen, amide carbonyl oxygen and oxygen
of pyranone ring by deprotonation in all metal complexes, but
in 2:1 ratio of ligand to metal the amide C=O coordinated
without deprotonation.
TGA
DTA
0
-5
-10
-15
-20
-25
-30
The band for O-H stretch at 3514 cm-1 in free ligand dis-
appears in [Zn(L)(H2O)].An additional band appearing at 3522
cm-1 is due to coordination of water molecule to metal ion.
Azomethine nitrogen band at 1595 cm-1 was shifted to lower
region at 1573 cm-1 indicating the coordination of azomethine
nitrogen to metal ion. The absence of band at 3134 cm-1 for
amide N-H stretch in complex indicates the coordination of
amide oxygen through enolate by deprotonation. Thus, from
IR data the ligand acts as monobasic for [Mn(HL)2], [Co(HL)2],
[Cu(HL)2], [Ni(HL)2] complexes and dibasic for [Zn(L)(H2O)],
[Cu(L)(H2O)] complexes.
100
200
300
Temperature (°C)
Fig. 1. TGA-DTA analysis of [Zn(L)(H2O)]
400
500
600
Electronic spectra: Electronic spectra of the synthesized
transition metal complexes were recorded in DMSO solvent
at room temperature. The complexes exhibited two bands in
the range 349-375 nm which were assigned for charge transfer
spectra observed after complex formation [23]. This indicated
the coordination of azomethine nitrogen to metal ions and
another band in the range of 280-290 nm corresponding to
the π→π* transition (Fig. 2).
NMR analysis: Two signals observed at 16.00 and 11.73
δ ppm correspond to enolic OH and amide NH respectively in
the 1H NMR spectrum of the free ligand. These signals were
Antimicrobial study: Antimicrobial activity of the synthe-
sized compounds was evaluated against one bacterial Strepto-
coccus aureus and two fungal species Aspergillums niger and
Alternaria alternata using petri plate method at 250 ppm con-
centration in DMSO solvent and compared with the standard
antibiotics - streptomycin and carbendazim respectively. The
petri plate (stains) containing 30 mL nutrient agar and potato
dextrose agar (PDA) medium for bacteria and fungi were
incubated for 20-24 h and 24-48 h respectively at 37 °C and
the zones of inhibition were measured in terms of mm. The
results were compared with the standard antibiotics. The metal
complexes showed more inhibitory effects than the non-coor-
dinated ligand against used species under identical condition.
FromTable-2, antibacterial activity of ligand and the synthe-
sized metal complexes was found to be less against Strepto-
coccus aureus as compared with the standard drug streptomycin.
However Cd(II) and Mn(II) complexes exhibited excellent
activity against Alternaria alternata than the standard drug
carbenzadim. The remaining compounds showed lesser
activity. On the other hand; Cd (II) complex exhibited excellent
activity against Aspergillums niger even more than the standard
drug carbendazim.
1
disappeared in H NMR spectrum of [Zn(L)H2O)] complex
indicating the coordination of these two sites via deprotonation.
The aromatic protons in the range of 7.902-8.092 δ ppm reso-
nating as multiplet in 1H NMR spectrum of non-coordinated
ligand have shifted slightly to downfield in the range 8.05-
8.16 δ ppm of metal complex. Two CH3 protons were observed
as singlets at 2.136 and 2.632 δ ppm in free ligand have moved
to 2.06 and 2.55 δ ppm respectively after formation of the
complex [22].
In 13C NMR spectrum of free ligand signals observed at
182.00 and 17.07 ppm corresponds to 2C (quat.) (DHA) and
azomethine(s) CH3 respectively were shifted to 178.86 and 19.19
δ ppm in the spectrum of [Zn(L)H2O)] complex, indicating
the coordination of ligand-OH via deprotonation. The azome-
thine carbon has moved to downfield in the spectrum of complex
indicating the participation of azomethine nitrogen in comp-
lexation with metal ion. The two aromatic quartets for carbons
observed at 121.80 and 133.68 δ ppm in the ligand were shifted
to downfield at 121.44 and 132.21 δ ppm, which also confirms
the coordination of amide NH via deprotonation.
Thermal analysis: Thermal study of metal complexes
gives an idea about the presence or absence of lattice or coordi-
nated held solvent molecules and is useful to confirm their
composition and thermal stability. The thermal analysis was
performed under nitrogen atmosphere in the temperature range
of 25-800 °C at a heating rate of 10 °C per min.
Conclusion
In conclusion, a new 3-bromo-2-[1-(4-hydroxy-6-methyl-
2-oxo-2H-pyran-3-yl)ethylidene] hydrazide ligand and its
transition metal complexes were synthesized and characterized.
Antimicrobial activity of the synthesized compounds revealed
that the Cd(II) complex shows excellent activity against fungal
species and Mn(II) complex shows moderate to good activity
against A. niger and Alternaria alternata, respectively. However,
antibacterial activity of all the screened compounds was found
to be less in comparison with the standard.
The thermogram of [Zn(L)H2O)] gives two peaks as shown
in Fig. 1. At about 260 °C, most of the organic material along
with water has been evaporated. Whereas at 450 °C, the metal
was converted to its oxide which is not decomposed upon
heating upto 600 °C.
Bhale
