Thermal decomposition of RE(C₂H₅CO₂)₃·H₂O (RE = Dy, Tb, Gd, Eu and Sm)

The thermal decomposition of Dy(III), Tb(III), Gd(III), Eu(III), and Sm(III) propionate monohydrates was studied in argon by means of simultaneous differential thermal analysis and thermogravimetry, infrared-spectroscopy, X-ray diffraction, and optical microscopy. After dehydration, which takes place below 120 °C, all salts decompose into dioxycarbonates with simultaneous release of CO2 and C2H5COC2H5 (3-pentanone) between 250 and 460 °C.

However, whereas the anhydrous Dy-, Tb-, and Gd-propionates appear to transform into RE2O2CO3 (rare earth [RE] = Dy, Tb, Gd) in a single step, an intermediate stage involving a RE2O(C2H5CO2)4 composition was evidenced in the case of the Eu- and Sm-propionates. For all compounds, further decomposition of RE2O2CO3 into the corresponding sesquioxides (RE2O3) is accompanied by the release of CO2.

The thermal decomposition of Dy- and Tb-propionates occurs entirely in the solid state. In contrast the dehydrated Gd-, Eu-, and Sm-propionates melt at increasingly higher temperatures. Evidence for recrystallization was found in conjunction with the onset of decomposition of these three propionates.