Enthalpies of formation of europium alkoxides: What lessons can be drawn from them

• First time measurement of europium(II) alkoxides enthalpy of formation.
• Calculation of alkoxides thermochemical radii and M–O distances in this environment.
• Comparison of experimental EXAFS distance with the calculated ones.
• Hints on the type of bond existing in these compounds.
• Correlation of bond type and possible use as catalysts.

The synthesis and characterization of two europium alkoxides, Eu(OCH3)2 and Eu(OC2H5)2, were described. For the first time the enthalpies of formation of divalent lanthanide alkoxides were determined by using reaction-solution calorimetry. The values obtained are ΔfH0ΔfH0 [Eu(OCH3)2,cr] = −850.5 ± 5.0 kJ/mol and ΔfH0ΔfH0 [Eu(OC2H5)2,cr] = −902.5 ± 5.5 kJ/mol, respectively. Since these compounds have a large use as catalysts or catalysts precursors, the first step of the reaction of them with CO2 was addressed, which permits to have an idea of the kind of bond involved in those compounds. Moreover, insertion of CO2 in the europium oxygen bond and formation of metal carboxylate complexes, is in both cases presumably bidentate.