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Inorg Chem. 2018 Jun 18;57(12):6965-6972. doi: 10.1021/acs.inorgchem.8b00654. Epub 2018 Jun 5.

Complexation of NpO2+ with Amine-Functionalized Diacetamide Ligands in Aqueous Solution: Thermodynamic, Structural, and Computational Studies.

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Chemical Sciences Division , Lawrence Berkeley National Laboratory , 1 Cyclotron Road , Berkeley , California 94720 , United States.
College of Nuclear Science and Technology , Harbin Engineering University , 150001 Harbin , China.
Department of Chemistry , University of California-Berkeley , Berkeley , California 94720 , United States.
Dipartimento Politecnico di Ingegneria e Architettura , Università di Udine, Laboratori di Chimica , via delle Scienze 99 , 33100 Udine , Italy.


Complexation of Np(V) with three structurally related amine-functionalized diacetamide ligands, including 2,2'-azanediylbis( N, N'-dimethylacetamide) (ABDMA), 2,2'-(methylazanediyl)bis( N, N'-dimethylacetamide) (MABDMA), and 2,2'-(benzylazanediyl)bis( N, N'-dimethylacetamide) (BnABDMA), in aqueous solutions was investigated. The stability constants of two successive complexes, namely, NpO2L+ and NpO2L2+, where L stands for the ligands, were determined by absorption spectrophotometry. The results suggest that the stability constants of corresponding Np(V) complexes follow the trend: MABDMA > ABDMA ≈ BnABDMA. The data are discussed in terms of the basicity of the ligands and compared with those for the complexation of Np(V) with an ether oxygen-linked diacetamide ligand. Extended X-ray absorption fine structure data indicate that, similar to the complexation with Nd3+ and UO22+, the ligands coordinate to NpO2+ in a tridentate mode through the amine nitrogen and two oxygen atoms of the amide groups. Computational results, in conjunction with spectrophotometric data, verify that the 1:2 complexes (NpO2(L)2+) in aqueous solutions are highly symmetric with Np at the inversion center, so that the f-f transition of Np(V) is forbidden and NpO2(L)2+ does not display significant absorption in the near-IR region.

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