FORMALLY TETRAVALENT CERIUM AND THORIUM COMPOUNDS - A CONFIGURATION-INTERACTION STUDY OF CEROCENE CE(C8H8)(2) AND THOROCENE TH(C8H8)(2) USING ENERGY-ADJUSTED QUASI-RELATIVISTIC AB-INITIO PSEUDOPOTENTIALS

Large-scale state-averaged multi-configuration self-consistent field, configuration interaction, averaged coupled-pair functional and spin-o rbit configuration interaction calculations have been carried out for the ground states and low-lying excited states of the bis(cyclooctatet raene)f-element sandwich complexes cerocene Ce(C8H8)(2) and thorocene Th(C8H8)(2). Whereas for a single-determinant wavefunction thorocene m ay be pictured as a Th-IV compound, i.e. a Th4+ closed-shell ion compl exed by two aromatic C8H82- ligands, cerocene is to a first approximat ion a Ce-III compound, i.e. a Ce3+ ion with a 4f(1) configuration and two C8H81.5- ligands. When cerocene is described by a multi-determinan t wavefunction admixture of the Ce4+ (C8H82-)(2) configuration leads t o a (1)A(1g) ground state of the same symmetry as in thorocene. For bo th compounds results for the metal-ring distance, the symmetric metal- ring stretching frequency, the photoelectron spectrum and the optical spectrum are compared to experimental data.