Mixed metal oxalate hydrazines

Mixed metal oxalate hydrazines containing iron as the common metal are prepared either from metal powders or metal salts. Stoichiometric quantities of the respective metal powders are dissolved in a solution of 

Mixed metal oxalate hydrazines of Mg and Co can also be obtained by the reaction of mixed metal oxalate hydrates MFe2(C204)3-6H20 with excess hydrazine hydrate [16,17]. 

Similar to the above, mixed metal oxalate hydrazines can be prepared with cobalt being the common metal. Stoichiometric quantities of the respective metal powders of magnesium and nickel are dissolved in a solution of ammonium oxalate in hydrazine hydrate. It takes a few hours for the metal powders to completely disperse into the solution. After their complete dissolution, alcohol is added to precipitate out the complex. The precipitate is further washed with alcohol and diethyl ether [18]  

The IR spectra of mixed metal oxalate hydrazines confirm the presence of coordinated oxalate and hydrazine groups. The spectra have characteristic absorptions of bidentate oxalate at 1650, 1320, 1300, and 

These complexes are crystalline solids with characteristic colors. As the reactions are carried out under reducing conditions, iron is present as Fe in these complexes. The presence of Fe makes them rather susceptible to atmospheric oxidation and they are unstable and decompose on storage, losing hydrazine. They need to be prepared and stored in an atmosphere of nitrogen. Table 3.15 gives the thermal decomposition temperatures of the complexes. 

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The mixed metal oxalate hydrazines exhibit autocatalytic behavior, and the product of combustion is the spinel MFe204. Interestingly, the precursors ignite while undergoing suction filtration if allowed to dry. 

Gajapathy, D. and Patil, K.C. (1983) Mixed metal oxalate hydrazinates as compound precursors to spinel ferrites. Materials Chemistry and Physics, 9, 423-438. 

Patil, K.C., Gajapathy, D., and Pai Verneker, V.R. (1983) Low temperature cobaltite formation using mixed metal oxalate hydrazine precursor. Journal of Materials Science Letters, 2, 272-274. 

When an aqueous solution of the metal salt of Fe, Co, and Ni is mixed with ammonium oxalate in hydrazine hydrate, the corresponding metal oxalate hydrazines are precipitated ... 

The formation of cobaltites (MC02O4) from the combustion of mixed metal oxalate/acetate hydrazine complexes and solid solutions of hydra-zinium metal hydrazine carboxylate hydrates have been discussed in Chapters 3 and 4, respectively (Sections 3.2.4.1, 3.2.6 and 4.6). The final product, confirmed by X-ray diffraction pattern, shows the characteristics of cobaltite spinels. Similar to cobaltites, mixed metal oxalate/acetate hydrazines complexes undergo single-step decomposition to form... 

Mixed metal oxalate hydrates do not yield ferrites at such low temperatures. However, complex formation with hydrazine makes it possible to obtain ferrites from the oxalates precursors at low temperatures of —150 °C. This shows that the exothermic decomposition of hydrazine plays a vital role in the formation of these spinels at such temperatures. Properties of the ferrites formed are summarized in Table 6.7. 

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