Coupled Cluster Studies of Platinum-Actinide Interactions. Thermochemistry of PtAnOn+ (n=0-2 and An = U, Np, Pu)

Accurate Pt-An bond dissociation enthalpies (BDEs) for PtAnO(n+) (An = U, Np, Pu and n = 0-2) and the corresponding enthalpies for the Pt + OAnO(n+) substitution reactions have been studied for the first time using an accurate composite coupled cluster approach. Analogous O-AnO(n+)' bond dissociation enthalpies are also presented. To make the study possible, new correlation consistent basis sets optimized using the all-electron third-order Douglas-Kroll-Hess (DKH3) scalar relativistic Hamiltonian are developed and reported for Pt and Au, with accompanying benchmark calculations of their atomic ionization potentials to demonstrate the effectiveness of the new basis sets. For the charged PtAnO(n+) species (n 1, 2), a low-spin state (LSS) for which the Pt-An sigma bond is doubly occupied is studied together with a high-spin state (HSS) obtained by unpairing the sigma bond orbital and placing one electron into the An Sf shell. The relative energies of the two spin states have been compared and qualitatively assessed via natural population and natural bond analyses. The enthalpies for the Pt substitution reactions, i.e., Pt + OAnO(n+) -> PtAnO(n+) + O, are calculated to range from about 14-62 kcal/mol, and the Pt-AnO(n+) bond dissociation enthalpies range from about 78-149 kcal/mol for the ground electronic states. For the PtAnO(+) species, the LSSs were all predicted to be the ground state, whereas the PtAnO(2+) molecules all favored the HSSs. The prediction for PtUO2+ is consistent with previous theoretical findings. The natural bond orbital analyses indicate a triple bond between An and O, with a double to quadruple bond between the An and Pt.

Automated summary

Accurate Pt-An bond dissociation enthalpies and substitution reactions for PtAnO(n+) have been studied for the first time using a composite coupled cluster approach. The calculations show a triple bond between An and O, and a double to quadruple bond between An and Pt.