Thermochemistry of bis[η8-cyclooctatetraene]thorium and bis[η8-cyclooctatetraene]uraium

Combustion heat ΔHc0 of bis[η8-cyclooctatetraene]thorium (thorocene) has been determined for the first time and ΔHc0 for bis[η8-cyclooctatetraene]uranium (uranocene) has been refined. On the basis of the data obtained using the results of tensiometric experiments the standard formation enthalpies of the compounds studied in condensed and gaseous states and mean dissociation energies of actinide-cyclooctatetraene bonds are calculated. It is pointed out that metal-ligand chemical bond in the compounds is the strongest one among the known sandwich complexes. Comparative evaluation of dissociation energies of all bonds in thorocene and uranocene shows that the mean energy of carbon-hydrogen bond is the determining factor of thermal destabilization of molecules in the compounds studied