The photochemistry of potassium trisoxalatoferrate(III) trihydrate in the solid state

The gaseous and solid state products of decomposition on uv exposure of polycrystalline K ₃[Fe(C ₂O ₄) ₃]·3H ₂O have been investigated by mass-spectrometry, ir- and Mössbauer spectroscopy, and chemical and X-ray phase analysis. CO ₂ and CO are obtained as photoproducts. The volume ratio, CO:CO ₂, generated depends on the exposure conditions and approximately equals 1:3 on photodecomposition in air and 1:2 on decomposition in vacuum. Comparison of the experimental and literature data leads to the following conclusions. The Fe(II)-containing final products of photolysis, radiolysis, and low-temperature (250-260°) thermal decomposition are identical; FeC ₂O ₄ is missing among the principal final solid state products. Arguments are presented in favor of the view that the Fe(II)-containing final products of photodecomposition is a polymer of composition (K ₂[Fe(C ₂O ₄) ₂]) _n. On the basis of the experimental and literature data, the flow sheet and stoichiometry of the photodecomposition has been determined. A comparison is made of the spectral dependences of photoconductivity and of photolysis in air. The type of charge carrier is established. Questions related to the mechanisms of photodecomposition are discussed.