Electronic structure of hydrated cerium(III). An INDO/S-CI molecular orbital study including spin-orbit interaction

INDO/S-CI calculations including spin-orbit interaction have been performed on model complexes [Ce(H₂O)_n]³⁺, n = 8, 9, to rationalize the electronic structure and the spectrum of hydrated Ce(III). We present the first molecular orbital investigation that calculates the transition energies and oscillator strengths for the cerium 8-fold and 9-fold coordinated hydrates and gives a quantitative interpretation of the solution spectrum. The transition moments and energies of the five observed 4f → 5d strong bands are very well reproduced by using an enneahydrated model complex with a distorted tricapped trigonal prismatic geometry. The influence of some structural variations of the enneahydrate on the spectrum are discussed and other more symmetric structures of the solvation shell are ruled out on account of the calculated transition energies. An additional weak band in the solution spectrum is attributed to an octacoordinated complex as a dissociative product.