A Quantum Mechanical Study of Ce(IV)-tetrakis(chatecolato) as a Model for Pu(IV) Coordination Chemistry

The increasing use of radioactive materials in private, medical, and weapons industries has generated interest in sequestering agents for use in oral chelation therapy and nuclear waste remediation, with particular interest in highly effective sequestering agents for Pu  and U.  Radioactivity and the complex chemical nature of Pu limits the ability to crystallize and study Pu complexes.  Fortunately, the lanthanides have been shown to be good models for studying aqueous actinide coordination chemistry.  In particular, the ionic size of Ce(IV) and the similarities between  coordination chemistries of Ce(IV) and Pu(IV) make Ce(IV) complexes good models for Pu(IV) complexes.  Chatecolato-based ligands have been designed specifically for Pu(IV) chelation, and the Ce(IV) – tetrakis(chatecholato) complex, consisting of Ce(IV) coordinated by four chatecholato ligands, has been crystallized.  This study focuses on a quantum mechanical treatment of the Ce(IV)-tetrakis(catecholato) complex to yield insights into its chemical nature.  Our calculations were carried out using density functional theory (DFT) with the B3LYP functional and the SDD basis sets.  Geometry optimization was performed, followed by a frequency calculation, yielding the equilibrium geometry, the vibrational frequencies and the infrared spectrum.    The calculated equilibrium geometry is compared to, and agrees with, existing crystallographic data.  The highest occupied molecular orbital (HOMO) – lowest occupied molecular orbital (LUMO) energy gap value (2.7 eV) suggests this complex is chemically stable.  The dipole moment is very small (0.0004 Debye), consistent with the complex’s highly symmetrical structure.  We predict similar chemical properties in the Pu(IV)-tetrakis(catecholato) complex.