1964
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
Semushina et al.
formed in an inert atmosphere, whereas metals are formed
in a hydrogen atmosphere. However, thermal analysis was
possible up to now only in air and argon atmospheres, and
experiments at particular temperatures were carried out in
hydrogen. In this work, to supplement the earlier obtained
data, the thermal analysis of compound [Co(NH3)6]ꢀ
[Fe(C2O4)3]•3H2O (1) was carried out for the first time
and the scheme of decomposition in a hydrogen atmoꢀ
sphere was constructed. The thermal analysis in a helium
atmosphere was carried out for comparison.
Results and Discussion
The thermal analysis curves for the BCC 1 obtainꢀ
ed in the atmosphere consisting of helium (94.2 vol.%)
and hydrogen (5.8 vol.%) are presented in Fig. 1. The
first step of decomposition occurs in the temperature
range 30—90 С, is accompanied by an endotherm, and
represents the removal of crystallization water molecules.
The mass loss in this step is 10.0%, and the water conꢀ
tent in the initial complex is 10.1%. Under the experiꢀ
mental conditions, the anhydrous product was stable
up to 160 С. The second step of mass loss occurs in
a temperature range of 160—250 С and is also accompaꢀ
nied by an endotherm. The third step occurs at 300—330 С,
results in an insignificant weight loss, and is accompanied
by an exotherm. The overall mass loss in the second and
third steps approximately corresponds to the removal of
six ammonia molecules and one oxalate group. According
to the Xꢀray phase analysis data, the product obtained at
300 С is amorphous to Xꢀrays (Fig. 2, curve 1). The comꢀ
pletion of the thermolysis process at 350 С followed
by Xꢀray phase analysis of the cooled product showed
an unidentified crystalline phase (see Fig. 2, curve 2).
The similar unit cell parameters of the phases Co3O4
(JCPDSꢀICDD No. 71ꢀ816)7 and Fe3O4 (JCPDSꢀICDD
No. 26ꢀ1136)7 do not allow one to determine unambiguꢀ
ously whether the M3O4 phase is a solid solution of cobalt
and iron oxides or a mixture of oxides. The fourth step of
thermal decomposition occurs in the temperature range
350—440 С and is accompanied by an endotherm. The
total mass loss is 78.6%, and the weight of the residue is
21.4%, which corresponds to stoichiometry of the CoFe
residue (the calculated value is 21.45%). The refined paraꢀ
meter of the bodyꢀcentered unit cell of the obtained phase
(a = 2.861 Å) indicates the formation of a solid solution
Co0.5Fe0.5 based on the crystalline lattice of iron. No suꢀ
Experimental
The synthesis of complex 1 was carried out by mixing aqueꢀ
ous solutions of equivalent amounts of [Co(NH3)6]Cl3 and
K3[Fe(C2O4)3] prepared according to described procedures.5
The following reagents were used: CoCl2•6H2O, FeCl3•6H2O,
K2C2O4•H2O, H2C2O4•2H2O, and КНСО3 (reagent grade),
as well as a concentrated solution of ammonia. The synthesized
compound was identified by Xꢀray phase analysis, chemical
analysis, and IR spectroscopy.4 For analysis to metals, weighed
samples of BCC were dissolved in a mixture of hydrochloric and
nitric acids and the metal content in solutions was determined
on an AAnalystꢀ400 spectrometer. Elemental analyses of the
samples to the content of C, H, and N were carried out on
a Euro EA 3000 instrument. Found (%): Со, 11.8; Fe, 10.3;
С, 13.5; H, 4.6; N, 15.6. Calculated (%): Со, 11.0; Fe, 10.4;
С, 13.5; H, 4.5; N, 15.7.
Thermogravimetric measurements were carried out in a reꢀ
ductive atmosphere (Не + 5.8 vol.% Н2) using a TG 209 F1 Iris
thermobalance (NETZSCH). The weight of the sample was
20 mg (Al2O3 crucible, flow rate 60 mL min–1, heating rate
10 deg min–1). Simultaneous thermal analysis (STA) was carried
out for comparison in inert (Не) and reductive (Не + 5.8 vol.%
Н2) atmospheres, including the simultaneous thermogravimetꢀ
ric (TG) determinations, differential scanning calorimetry
(DSC), and mass spectrometric analysis (MS) of the isolated gas
on an STA 449 F1 Jupiter instrument (NETZSCH) combined
with a QMS 403DAëolos quadrupole mass spectrometer. The
weight of the sample was 20 mg (Al2O3 crucible, gas flow rate
30 mL min–1, heating rate 10 deg min–1). Experimental
data were processed using the Proteusanalysis standard program
package.6
DTG (% min–1
DTA/К
)
m (%)
exo
100 С, 90.0%
1
100
Point experiments were also carried out. Weighed samꢀ
ples of BCC placed in a quartz boat were heated in a hydroꢀ
gen flow (15 L h–1, GVChꢀ12 as a hydrogen source) in a quartz
tubular reactor mounted into a SNOLꢀ0.2/1250 tubular furꢀ
nace. The reactor was taken from the furnace immediately afꢀ
ter a required temperature was attained and cooled in the
same atmosphere. Solid thermolysis products were anaꢀ
lyzed to the content of metal and carbon and subjected to
Xꢀray phase analysis. The JCPDSꢀICDD database was used
for the identification of the crystalline products.7 Gaseous therꢀ
molysis products were captured passing the outlet gas flow
consequently through Drexel bottles with titrated solutions
of HCl and NaOH. The amounts of evolved ammonia and
СО2 were determined in these solutions using titration by
two indicators.8
0
0
90
80
70
60
50
40
30
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
2
3
–2
–4
–6
–8
450 С, 21.4%
–10
50 100 150 200 250 300 350 400 450 T/°С
Fig. 1. Thermal analysis curves for complex 1 in a gas mixture
of helium (94.2 vol.%) and hydrogen (5.8 vol.%): TG (1),
DTG (2), and DTA (3).
Semushina, Yu. P.
