Formally tetravalent cerium and thorium compounds: a configuration interaction study of cerocene Ce(C8H8)2 and thorocene Th(C8H8)2 using energy-adjusted quasirelativistic ab initio pseudopotentials Original Research Article

Large-scale state-averaged multi-configuration self-consistent field, configuration interaction, averaged coupled-pair functional and spin-orbit configuration interaction calculations have been carried out for the ground states and low-lying excited states of the bis(cyclooctatetraene)f-element sandwich complexes cerocene Ce(C8H8)2 and thorocene Th(C8H8)2. Whereas for a single-determinant wavefunction thorocene may be pictured as a ThIV compound, i.e. a Th4+ closed-shell ion complexed by two aromatic C8H82− ligands, cerocene is to a first approximation a CeIII compound, i.e. a Ce3+ ion with a 4f1 configuration and two C8H81.5− ligands. When cerocene is described by a multi-determinant wavefunction admixture of the Ce4+ (C8H82−)2 configuration leads to a 1A1g ground state of the same symmetry as in thorocene. For both 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.