Thermal decomposition of Prussian blue analogues of the type Fe[Fe(CN)5NO]

The structure and properties of the thermal decomposition products of Fe[Fe(CN)₅NO] · x H₂O (x = 5 ~ 6) have been studied by Mossbauer and FT-IR spectroscopy, X-ray diffraction, and conductivity measurements. The valence state and coordination environment of the iron ions change dramatically when the nitrosyl ligand is eliminated by heat-treatment under vacuum at 200 °C. The dark blue product obtained by heat-treatment under vacuum at 250 °C is characteristic of the mixed-valence state in Prussian blue analogues. The electrical conductivity of the dark blue product is higher by a factor of 103 than that of the starting material because of the mixed-valence state between Fe(III)[Fe(II)(CN)₅] and Fe(II)[Fe(III)(CN)₅]. Heat-treatment under vacuum at 350°C yields a new product Fe(II)[Fe(II)(CN)₄] the crystal structure of which is different from that of the starting material. The electrical conductivity of the decomposition product obtained at 350 °C is about 10⁵ times higher than that of the starting material.