Bonding trends across the series of tricarbonato-actinyl anions [(AnO2)(CO3)3]4- (An = U-Cm): the plutonium turn

Jian-Biao Liu; Guo P Chen; Wei Huang; David L Clark; W H Eugen Schwarz; Jun Li

doi:10.1039/c6dt03953g

Bonding trends across the series of tricarbonato-actinyl anions [(AnO₂)(CO₃)₃]^4- (An = U-Cm): the plutonium turn

Dalton Trans. 2017 Feb 21;46(8):2542-2550. doi: 10.1039/c6dt03953g.

Authors

Jian-Biao Liu¹, Guo P Chen², Wei Huang², David L Clark³, W H Eugen Schwarz⁴, Jun Li⁵

Affiliations

¹ College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in Universities of Shandong, Shandong Normal University, Jinan 250014, China and Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084, China. junli@tsinghua.edu.cn.
² Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084, China. junli@tsinghua.edu.cn.
³ Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
⁴ Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084, China. junli@tsinghua.edu.cn and Physical and Theoretical Chemistry, University of Siegen, 57068, Germany.
⁵ Department of Chemistry and Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084, China. junli@tsinghua.edu.cn and Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.

PMID: 28154870
DOI: 10.1039/c6dt03953g

Abstract

Actinyl-tricarbonato anions [(AnO₂)(CO₃)₃]^4- (An = U-Cm) in various environments were investigated using theoretical approaches of quantum-mechanics, molecular-mechanics and cluster-models. Cations and solvent molecules in the 2^nd coordination sphere affect the equatorial An←O_eq bonds more than the axial An[triple bond, length as m-dash]O_ax bonds. Common actinide contraction is found for calculated and experimental axial bond lengths of ₉₂U to ₉₄Pu, though no longer for ₉₄Pu to ₉₆Cm. The tendency of U to Pu forming actinyl(vi) species dwindles away toward Cm, which already features the preferred An^III/Ln^III oxidation state of the later actinides and all lanthanides. The well known change from d-type to typical U-Pu-Cm type and then to f-type behavior is labeled as the plutonium turn, a phenomenon that is caused by f-orbital energy-decrease and f-orbital localization with increase of both nuclear charge and oxidation state, and a non-linear variation of effective f-electron population across the actinide series. Both orbital and configuration mixing and occupation of antibonding 5f type orbitals increase, weakening the AnO_ax bonds and reducing the highest possible oxidation states of the later actinides.