Thermal and structural changes of lanthanum hexacyanocobaltate(III) pentahydrate, La[Co(CN)6]⋅5H2O were investigated by means of thermal analysis, visible electronic spectra, IR, powder X-ray diffraction, EXAFS and TG-MS.
The dehydration of La[Co(CN)6]⋅5H2O proceeded reversibly through three steps and steps corresponded to the losses of H2O, 3H2O and H2O, and the enthalpy changes for these steps were 51.3, 211.0 and 38.7 kJ mol−1, respectively.
After the dehydration, the colour of the anhydride changed from white to blue around 290C and an abrupt mass loss occurred
at 350C. The colour change seems to be attributable to the change of coordination geometry around the Co ions from an octahedral
structure to a tetrahedral one. LnCoO3 was obtained as a final product by heating the sample to 1000C.