Two interpretations of the cerocene electronic ground state

Two alternative interpretations are given for the electronic ground state of bis-η8-annulene[8] cerium, cerocene, based on the same relativistic Douglas–Kroll–Hess complete active space all-electron wavefunction. Rotations in the spaces of the one- and many-electron wavefunctions, leaving the total energy invariant, show that the system can be viewed as a complex of a closed-shell Ce(IV) ion sandwiched by two aromatic annulene[8] dianions and bonded with a significant Ce 4f – ring π covalency, or as a Ce(III) ion with an almost atomic-like 4f1 subconfiguration, coupled to the unpaired electron in the rings highest energy occupied π orbitals in a Kondo-type fashion.