Coordination of 2,2′-(Trifluoroazanediyl)bis(N,N′‑dimethylacetamide) with U(VI), Nd(III), and Np(V): A Thermodynamic and Structural Study

• Published in: Inorganic chemistry 2019-12, Vol.58 (23), p.15962-15970
• Main Authors: Gao, Yang, Parker, Bernard F, Dau, Phuong V, Dau, Phuong D, Lohrey, Trevor D, Gibson, John K, Arnold, John, Teat, Simon J, Melchior, Andrea, Zhang, Zhicheng, Rao, Linfeng
• Format: Article
• Language: English
• Subjects: Amine-bridged diacetamide; Complexation; Coordination mode; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Neodymium; Neptunium; Thermodynamics; Uranium
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b02469

Thermodynamic properties of the complexation of 2,2′-(trifluoroazanediyl)­bis­(N,N′-dimethylacetamide) (CF3ABDMA) with U­(VI), Nd­(III), and Np­(V) have been studied in 1.0 M NaNO3 at 25 °C. Equilibrium constants of the complexation were determined by potentiometry and spectrophotometry. In comparison with a series of structurally related amine-bridged diacetamide ligands, including 2,2′-(benzylazanediyl)­bis­(N,N′-dimethylacetamide) (BnABDMA), 2,2′-azanediylbis­(N,N′-dimethylacetamide) (ABDMA), and 2,2′-(methylazanediyl)­bis­(N,N′-dimethylacetamide) (MABDMA), CF3ABDMA forms weaker complexes with U­(VI), Nd­(III), and Np­(V) due to the lower basicity of the center N atom in CF3ABDMA resulting from the attachment of the strong electron-withdrawing CF3- moiety. The complexation strength of CF3ABDMA with the three metal ions follows the order: UO2 2+ > Nd3+ > NpO2 +, consistent with the order of the “effective” charges of the metal ions. Structural information on the U­(VI)/CF3ABDMA complexes in solution and in solid was obtained by theoretical computation, single crystal X-ray diffractometry, 19F NMR, and electrospray ionization mass spectrometry. The structural data indicate that, similar to the three previously studied amine-bridged diacetamide ligands (BnABDMA, ABDMA, and MABDMA), the CF3ABDMA ligand coordinates to UO2 2+ in a tridentate mode, through the center nitrogen and the two amide oxygen atoms.