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

Yang Gao; Bernard F Parker; Phuong V Dau; Phuong D Dau; Trevor D Lohrey; John K Gibson; John Arnold; Simon J Teat; Andrea Melchior; Zhicheng Zhang; Linfeng Rao

doi:10.1021/acs.inorgchem.9b02469

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

Inorg Chem. 2019 Dec 2;58(23):15962-15970. doi: 10.1021/acs.inorgchem.9b02469. Epub 2019 Nov 12.

Authors

Yang Gao^{1

2}, Bernard F Parker^{1

3}, Phuong V Dau¹, Phuong D Dau¹, Trevor D Lohrey^{1

3}, John K Gibson¹, John Arnold^{1

3}, Simon J Teat⁴, Andrea Melchior⁵, Zhicheng Zhang¹, Linfeng Rao¹

Affiliations

¹ Chemical Sciences Division , Lawrence Berkeley National Laboratory , 1 Cyclotron Road , Berkeley , California 94720 , United States.
² College of Nuclear Science and Technology , Harbin Engineering University , Harbin 150001 , China.
³ Department of Chemistry , University of California - Berkeley , Berkeley , California 94720 , United States.
⁴ Advanced Light Source , Lawrence Berkeley National Laboratory , 1 Cyclotron Road , Berkeley , California 94720 , United States.
⁵ Dipartimento Politecnico di Ingegneria e Architettura , Università di Udine, Laboratori di Chimica , via delle Scienze 99 , 33100 Udine , Italy.

PMID: 31713423
DOI: 10.1021/acs.inorgchem.9b02469

Abstract

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: UO₂²⁺ > 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 UO₂²⁺ in a tridentate mode, through the center nitrogen and the two amide oxygen atoms.