Complexation of actinyls by carboxylic acids as models for complexes with humic substances

INOR 106

Notker Roesch, roesch@ch.tum.de, Florian Schlosser, and Sven Krueger. Theoretische Chemie, TU Muenchen, Lichtenbergstrasse 4, 85748 Garching, Germany
We applied an all-electron relativistic density functional method to monocarboxylate complexes of actinyls in aqueous solution. Focusing on uranyl, we compared complexes with different carboxylic acids as well as different coordination modes of this functional group. Structural and energetic results were found to be similar for aliphatic and aromatic acids. Bidentate coordination is favored as a thermodynamic effect. Comparison to EXAFS results for carboxylic and humic acids shows that average equatorial U-O distances for uranyl are mainly determined by the coordination number. We discuss the implications of these findings for the actinyl complexation by humic substances.