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S. Yasodhai et al. / Thermochimica Acta 338 (1999) 57±65
2. Experimental
ture for crystallisation. The products separated after
two days were ®ltered, washed successively with
water, alcohol and ether and dried in air. In the case
of cadmium, the product was obtained immediately
after the addition of the ligand solution.
2.1. Preparation of the complexes
Citric acid is a tribasic acid and is expected to form
simple salts with hydrazine. However, attempts to
isolate simple salts and use them as ligands were
unsuccessful. Hence, an aqueous mixture containing
citric acid and hydrazine hydrate in different mole
ratios was used as a ligand for the preparation of the
complexes.
Cu2(cit)N2H42H2O. This complex was prepared by
the addition of an aqueous solution (50 cm3) of citric
acid monohydrate (1.05 g, 0.01 mol) and hydrazine
hydrate (0.25 cm3, 0.01 mol) to an aqueous solution
(50 cm3) of copper nitrate trihydrate (1.208 g,
0.01 mol). The product immediately formed was sepa-
rated from the solution after 15 min and washed with
water, alcohol and ether and air dried. Excess addition
of hydrazine hydrate, that is more than 0.04 mol
reduced the Cu(II) to metallic copper.
All the complexes were highly insoluble in water
except dihydrazinium nickel citrate tetrahydrate
which is partially soluble in cold water, but completely
soluble in hot water. All are insoluble in alcohol and
all other organic solvents and are stable in air and
insensitive to light.
N2H5M(Hcit)H2O, where M = Mn, Co, Ni or Zn(II).
These complexes were prepared by the addition of an
aqueous solution (50 cm3) containing a mixture of
citric acid monohydrate (1.05 g, 0.01 mol) and hydra-
zine hydrate (0.75 cm3, 0.03 mol) to the respective
metal nitrate hexahydrates (e.g., 1.455 g, 0.01 mol of
Co(NO3)26H2O; in the case of Mn, manganese(II)
acetate tetrahydrate 1.225 g, 0.01 mol was used) in
distilled water (50 cm3). The resulting clear solution
(pH < 6) was concentrated to about half volume and
left at room temperature to crystallise. After three
days, the crystalline products were separated from the
solutions and washed successively with distilled
water, alcohol and ether and dried in air. Nickel
complex was separated by the addition of alcohol.
(N2H5)2Ni(cit)4H2O. The reaction of an aqueous
solution (50 cm3) of nickel nitrate hexahydrate
(1.46 g, 0.01 mol) with an aqueous solution
(50 cm3) containing citric acid monohydrate (1.05 g,
0.01 mol) and hydrazine hydrate (1 cm3, 0.04 mol)
yielded the titled product. While concentrating the
resulting solution (pH 6 to 7), small amounts of
product separated from the solution, but this was
re-dissolved in the mother liquor as a clear solution.
The product separated from the concentrated solution
was washed with cold water, alcohol and dried in
vacuo.
2.2. Physico-chemical techniques
All the chemicals used were pure commercial grade
and the solvents were distilled before use. The hydra-
zine content of the complexes was determined volu-
metrically using a standard KIO3 solution (0.025 M)
under Andrews' conditions [26]. The metals after
destroying the organic part and hydrazine by treatment
with concentrated HNO3 and evaporating the excess
HNO3, were determined volumetrically by EDTA
titration. The re¯ectance spectra of the powdered
complexes were recorded on a Shimadzu 240-A
UV-Visible spectrophotometer in the 200±800 nm
range. The magnetic susceptibility measurements
were carried out using
a Gouy balance and
Hg[Co(NCS)4] as the calibrant at room temperature.
IR spectra were recorded as KBr pellets with a Perkin-
Elmer 597 model spectrophotometer in the 4000±
M3(Hcit)26N2H4, where M = Co, Ni, Zn or Cd. To
an aqueous solution (50 cm3) of the respective metal
nitrate hexahydrates (e.g., 1.455 g of Co(NO3)26H2O,
0.01 mol), an aqueous mixture (50 cm3) containing
citric acid monohydrate (1.05 g, 0.01 mol) and hydra-
zine hydrate (1.5 cm3, 0.06 mol) was added slowly
with constant stirring. The resulting clear solution
(pH > 8) was concentrated on a water bath to half
of its original volume except for cadmium. The con-
centrated solutions were left aside at room tempera-
1
200 cm
range. Simultaneous TG-DTA measure-
ments were carried out on a STA 1500 thermal ana-
lyser. The experiments were carried out in air using
platinium cups as sample holders with 5±10 mg of the
samples at the heating rate of 108C min 1. X-ray
powder diffraction patterns were obtained using a
Philips X-ray diffractometer model PW 1050/70
and Cu Kꢀ radiation with Ni ®lter.
Yasodhai
