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K. DEEPA ET AL.
complex is stable up to 2348C revealing the absence of any
water or solvent molecules in the complex. In the first stage
(234–2888C) a mass loss of 42.2% is attributed to the pyrolytic
removal of one of the nitrate ions and half of the ligand. The IR
spectrum of the residue after first stage also confirms the
presence of nitrate ions and ligand portions. In the second
stage (288–4688C), a mass loss of 32% was observed that is
due to the removal of rest of the ligand portion. The IR
spectrum of the residue after this stage confirms the absence
of any ligand portions. In the third stage (468–518 8C), the
mass loss of 8.8% is assigned to the removal of the remaining
nitrate ion. The final residue is quantitatively proved to be
anhydrous cadmium oxide.
FIG. 1. 1,2-Di(imino-40-antipyrinyl)ethane.
showing the coordination of both carbonyl oxygens (Radhak-
rishnan et al., 1984). An intense band of GA at 1576 cm21
attributable to the C55N stretch in GA (Madhu and Radhakrish-
nan, 2001b), is shifted to the region 1593–1605 cm21 in com-
plexes indicating the coordination of both azomethine
nitrogens (Marykutty et al., 2001). The perchlorate complex
shows an intense, broad and unsplit band at 1094 cm21 assign-
able to the n3 vibration of uncoordinated perchlorate ion
having Td symmetry. This is supported by another sharp band
of medium intensity at 622 cm21 due to the n4 vibration of per-
chlorate ion having Td symmetry (Scholar et al., 1975). For the
nitrate complex, a very strong band observed at 1370 cm21 is
attributable to the n3 vibration of uncoordinated nitrate ion
having D3h symmetry (Gatehouse et al., 1958). This is supported
by another band of medium intensity at 820 cm21, which is
assignable to the n2 vibration of nitrate (D3h) ion (Ajithkumar
and Radhakrishnan, 2002). In Far IR spectra of the halide com-
plexes, the Cd–Cl, Cd–Br and Cd–I stretching vibrations occur
at 235, 209 and 167 cm21 respectively, which are absent in the
spectrum of the free ligand.
The non-isothermal kinetic aspects of these pyroltic decompo-
sitions were carried out by the application of Coats–Redfern
method (Coats and Redfern, 1964). The kinetic parameters,
namely, the activation energy (E), the pre-exponential factor
(A) and the entropy of activation (DS) were calculated (given
in Table 5). There is no particular trend for E, A or DS among
the different stages of degradations. Based on the results of
present physicochemical investigations, the structures shown in
Figure 2 and Figure 3 may be assigned to the reported complexes.
EXPERIMENTAL
Materials
The cadmium salts were prepared from Analar cadmium
carbonate by dissolving it in respective 50% acids (Merck)
and then crystallizing out salts by evaporating the solution on
a steam bath. The 4-aminoantipyrine and glyoxal were pur-
chased from Aldrich Chemical Co., USA. The Schiff base
1,2-di(imino-40-antipyrinyl)ethane (GA) was prepared and
characterized as reported earlier (Madhu and Radhakrishnan,
2000b). Solvents used were either GPR or AR grade (Merck,
India; BDH, India or SRL, India).
The above results along with conductance data indicate that
perchlorate and nitrate anions remain as counter ions, while the
halide ions are coordinated to the metal ion in these complexes.
Electronic Spectra
The electronic spectral data of GA and the complexes in
solid state (using Nujol) with tentative assignments are pre-
sented in Table 4. The electronic spectra of GA shows two
Preparation of Complexes
Perchlorate Complex
First, 1 mmol of Cd(ClO4)22 6H2O in ethyl acetate (10 mL)
band maxima at 26,180 and 39,220 cm21 corresponding to
.
ꢁ
n ! pꢁ and p ! p transitions respectively (Madhu and
was added drop wise to the boiling suspension of the Schiff
base (1.2 mmol) in ethyl acetate (100 mL). This mixture was
refluxed for about 2 h on a steam bath. The precipitated
complex was filtered and washed with hot ethyl acetate to
remove any excess ligand. The complexes were then recrystal-
lized from methanol, dried over phosphorous(V) oxide and
kept under vacuum. (Warning! Perchlorate salts with
organic compounds are potentially explosive. They should be
handled in small quantities and with caution.)
.
Radhakrishnan, 2001b). In complexes the n ! pꢁ bands are
found to be red shifted to the region 21,881–24,271 cm21
while the p ! pꢁ band is found to be blue shifted to
.
the region 39,370–40,322 cm21 compared to that of GA. The
electronic spectra of all the complexes exhibit an intense
absorption band in the region 32,362–33,444 cm21 that
might be due to a charge transfer process.
Thermal Behavior and Kinetic Aspects
Nitrate, Chloride, Bromide and Iodide Complexes
2
The TG data for cadmium(II) nitrate complex is presented in
Table 5. The thermal decomposition studies were carried out in
Here, 1 mmol of Cd(NO3)22 4H2O, CdCl2 2H2O, CdBr2 or
.
.
the temperature range 30–8008C. The three-stage decompo- CdI2 in methanol (10 mL) was added drop-wise to the boiling
sition pattern leads to the following conclusions. The suspension of the Schiff base (1.2 mmol) in ethyl acetate
Deepa
