Ce in the +4 oxidation state: Anion photoelectron spectroscopy and photodissociation of small CexOyHz− molecules

Abstract

The anion photoelectron (PE) spectra of a range of small mono-cerium molecular species, along with the CeO and CeO stoichiometric clusters, are presented and analyzed with the support of density functional theory calculations. A common attribute of all of the neutral species is that the Ce centers in both the molecules and clusters are in the +4 oxidation state. In bulk ceria (CeO), an unoccupied, narrow 4f band lies between the conventional valence (predominantly O 2p) and conduction (Ce 5d) bands. Within the CeO, CeOH, and Ce(OH) series, the PE spectra and computational results suggest that the Ce 6s-based molecular orbital is the singly occupied HOMO in CeO but becomes destabilized as the Ce 4f-local orbital becomes stabilized with increasing coordination. CeO, a hyperoxide, undergoes photodissociation with 3.49 eV photon energy to form the stoichiometric neutral CeO and O. In the CeO, CeO ,and CeO stoichiometric cluster series, the 6s destabilization with 4f stabilization is associated with increasing cluster size, suggesting that a bulk-like band structure may be realized with fairly small cluster sizes. The destabilization of the 6s-based molecular orbitals can be rationalized by their diffuse size relative to Ce-O bond lengths in a crystal structure, suggesting that 6s bands in the bulk may be relegated to the surface.

On the linear geometry of lanthanide hydroxide (Ln-OH, Ln = La–Lu)

“…In recent studies, Chick Jarrold and coworkers presented the structure and bonding of various lanthanide oxides and hydroxides, some of which involve multiple lanthanide-oxygen bonds. 1,14,[76][77] In agreement with our results, their experimental photoelectron spectroscopic studies and supporting DFT calculations have shown that Ln(I) complexes (e.g.…”

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

“…In recent studies, Chick Jarrold and coworkers presented the structure and bonding of various lanthanide oxides and hydroxides, some of which involve multiple lanthanide-oxygen bonds. 1,14,[76][77] In agreement with our results, their experimental photoelectron spectroscopic studies and supporting DFT calculations have shown that Ln(I) complexes (e.g. EuOH 1 ) favor a linear geometry, while lanthanide complexes with a higher coordination number (two or more hydroxide ligands coordinated to the lanthanide center) and corresponding higher lanthanide oxidation state (+2, +3, etc.)…”

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

“…yield bent Ln-O-H angles between 140 o and 160 o . 14,77 Table S2. Occupations of 4f, 5d, and 6s based non-bonding molecular orbitals of lanthanide hydroxides as described in the paper.…”