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

Abstract

Abstract 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(C 8 H 8 ) 2 and thorocene Th(C 8 H 8 ) 2 . Whereas for a single-determinant wavefunction thorocene may be pictured as a Th IV compound, i.e. a Th 4+ closed-shell ion complexed by two aromatic C 8 H 8 2− ligands, cerocene is to a first approximation a Ce III compound, i.e. a Ce 3+ ion with a 4f 1 configuration and two C 8 H 8 1.5− ligands. When cerocene is described by a multi-determinant wavefunction admixture of the Ce 4+ (C 8 H 8 2− ) 2 configuration leads to a 1 A 1g 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.