CALCULATED PROPERTIES OF LANTHANOCENE ANIONS AND THE UNUSUAL ELECTRONIC-STRUCTURE OF THEIR NEUTRAL COUNTERPARTS

Selected lanthanocene anions M(C8H8)(2)(-) (M = Ce, Nd, Tb, Yb) and th eir neutral counterparts have been investigated with large-scale compl ete-active-space self-consistent field calculations followed by multir eference configuration interaction and averaged coupled-pair functiona l calculations. Relativistic effects were included by means of energy- consistent ab initio pseudopotentials. It is shown that, in contrast t o the neutral actinocenes (e.g., M = Th, U), all corresponding lanthan ocenes are best described as resulting from trivalent rather than tetr avalent central atoms. In addition, the independent-particle model fai ls to predict the unusual electronic ground states of the Ce, Nd, and Tb systems. The electron affinities of the still hypothetical lanthano cenes beyond the well-known cerocene are found to be almost independen t of the central metals and to be substantially higher than those of t he corresponding actinocenes. The differences in the electronic struct ure between lanthanocenes and actinocenes can be explained by the diff erent impacts of relativistic effects, especially on the metal d and f orbitals.