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Indian Journal of Chemistry Vol. ~IA. September 198~. pp 9~0-921 Not es Mossbauer Study of Thermal Decomposition of Ferrous Oxalate & Ferric Nitrate AS BRAR*t & K S KHABRE Chemistry Department. Guru Nanak Dev University. Arnritsar 143005 Received 29 August 1980; revised 3 April 1982; accepted 9 July 1982 Thermal decomposition, of ferrous oxalate and ferric nitrate has been studied upto 900C in air and the thermal behaviour investigated using Mossbauer, infrared spectroscopy. DTA and TG. In the case offerrous oxalate. dehydration starts after lOOT and the compound is simultaneously converted into ferric oxalate which is decomposed completely to x-Fe-O, at 400 C. Mossbauer spectra of ferric nitrate samples heated at different temperatures for 3 hr show the presence of at-Fe20, at 200 C. the crystal structure of which does not change upto 900 C. Mossbauer spectroscopy is a useful tool for the investigation of changes in oxidation states of metal ions and structure elucidation of intermediates formed in the solid state reactions of metal salts ' 3. Ferrous oxalate and ferric nitrate are two important materials for the preparation of oxides of iron for use as catalysts. Their thermal behaviour (DT A and TG) has been investigated. The thermal behaviour of ferrous oxalate depends on the experimental conditions employed and different intermediates are reported to be formed. depending upon the atmosphere employed. e.g. the decomposition of ferrous oxalate is sensitive to oxygen 57 . In the present work nature of the intermediate formed during the decomposition of ferrous oxalate and ferric nitrate in air at different temperatures in the range IOO-900°C has been investigated by Mossbauer, infrared spectroscopy, DT A and TG techniques. Ferric nitrate and ferrous oxalate (both BDH, AR) were heated at a heating rate of IOCC/min in air at 100, 200 c • 300 , 400, 500' , 800 0 and 900°e. The samples were kept at the desired temperature for 3 hr. The chemical composition of the oxides was determined by chemical analysis", The Mossbauer spectra were recorded at room temperature (25' ± 2 C) on a Mossbauer spectrometer MBS-35 (ECIL, India) attached to a multichannel analyser MCA-38B wIth constant acceleration drive. 57CO (Rh) source (5 mci) was used for this purpose. The velocity of the drive was calibrated with sodium nitroprusside and with natural iron foil. All the values of isomer shifts have been reported with respect to t Present address: Chemistry Department. lIT. New Delhi 110016 920 sodium nitroprusside. The error in the isomer shift and quadrupole splitting values is 0.05 mm see -1. Infrared spectra were recorded on a Perkin-Elmer infrared spectrophotometer. DT A and TG were done on a derivatograph (MoM. Hungary). The ferrous oxalate (FeC 2 0 4 2H 2 0) (I) and ferric nitrate (II) were heated at different temperatures and were labelled as la and IIa at room temperature, Ib, lIb (at 100); Ie. lIe (at 200); Id. lId (at 300'); Ie, lIe (at 400); If, IIf (at 500); lg, IIg (at 800'); and Ih, IIh (at 900 C) respectively. Mossbauer spectra of ferrous oxalate sample Ia exhibits a doublet having an isomer shift of 1.40 mm see - t and quadrupole splitting values of 1.79 mm see - t in agreement with the values reported in literature". These parameters indicate that iron in this sample is in high spin state having + 2 oxidation state. The large value of quadrupole splitting is due to the asymmetric distribution of electrons in the valence shell and different ligands attached to iron atom (water and oxalate). Infrared spectrum of la exhibits bands at 3100-3400 and at 1640 em -1, due to the presence of water and oxalate group. The room temperature Mossbauer spectrum of ferric nitrate sample (Ila) is not a sharp single line but has a complex intensity distribution which is due to spin lattice relaxation to. This spectrum is similar to the spectrum of potassium ferrioxalate ll . A rough approximation of the isomer shift of 0.35 mm see t shows that iron in IIa is in high spin state in 3 + oxidation state. The oxalate sample (Ib) does not show any change in its Mossbauer spectrum when compared with that of sample (la). However the intensity of IR band at 3300- 3600 em -I due to water molecules decreases as compared to that of la showing partial loss of water molecules. This is supported by TG and an endothermic peak '" 120° in its DT A. The nitrate sample lIb got Iiquified at lOoue. It is evident from the above observations that only water is lost from ferrous oxalate at 100 G e. The Mossbauer spectra of oxalate and nitrate samples Ic and lIe respectively are different from those of la and IIa. The values of isomer shift and quadrupole splitting for Ie (0.50 and 0.62 mm see - t respectively) are in agreement with the reported values 12 but lower than those of the samples la. These values indicate that iron in sample Ie is III + 3 high spin state, probably due to the formation of ferric oxalate. Alongwith the doublet slight formation of six-line pattern due to formation of il-Fe203 also appears in the Mossbauer spectrum of Ie. The Mossbauer spectrum of nitrate sample IIc exhibits a six-line pattern having isomer shift 0.63 mm see -I,
