Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH2.76O3.89 (Adams' catalyst) and dehydrated oxide PtO2.52 at T=298.15 K were determined to be -519.6+/-1.0 and -101.3 +/-5.2 kJ mol(-1), respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO2 was estimated to be -80 kJ mol(-1) based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol(-1) at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric.