Density functional theory investigations on the binding modes of amidoximes with uranyl ions†
Density functional theory (DFT) calculations have been carried out to examine the relative facilities of different coordination modes of aromatic amidoximes (AOs) with UO2(NO3)2. Various η1-, η2- and chelated κ2-coordination modes of the possible neutral AO, tautomerized neutral (TAO, with the hydroxylic hydrogen transferring to the oximic nitrogen atom) and anionic amidoxime (AAO, formed by the deprotonation of AO) were examined. The results indicate that η1-O of the TAO and η1-O/η2-NO of AAO are the most plausible coordination modes. Three types of uranyl complexes, i.e. UO2(NO3)2(TAO)(AAO), UO2(NO3)2(AAO)2 and UO2(EtOH)2(AAO)2 are the predominant binding structures. The good consistency between the calculation results and the experimental observations verifies the proposed conclusions.