Multiple Bonding in Lanthanides and Actinides: Direct Comparison of Covalency in Thorium(IV)- and Cerium(IV)-Imido Complexes

A series of thorium­(IV)-imido complexes was synthesized and characterized. Extensive experimental and computational comparisons with the isostructural cerium­(IV)-imido complexes revealed a notably more covalent bonding arrangement for the CeN bond compared with the more ionic ThN bond. The thorium-imido moieties were observed to be 3 orders of magnitude more basic than their cerium congeners. More generally, these results provide unique experimental evidence for the larger covalent character of 4f05d0 Ce­(IV) multiple bonds compared to its 5f06d0 Th­(IV) actinide congener.