Coordination Structures of the Uranyl(VI)-Diamide Complexes: A Combined Mass Spectrometric, EXAFS Spectroscopic, and Theoretical Study

Xiuting Chen; Qingnuan Li; Yu Gong

doi:10.1021/acs.inorgchem.9b00047

Coordination Structures of the Uranyl(VI)-Diamide Complexes: A Combined Mass Spectrometric, EXAFS Spectroscopic, and Theoretical Study

Inorg Chem. 2019 May 6;58(9):5695-5702. doi: 10.1021/acs.inorgchem.9b00047. Epub 2019 Mar 25.

Authors

Xiuting Chen^{1

2}, Qingnuan Li¹, Yu Gong¹

Affiliations

¹ Department of Radiochemistry, Shanghai Institute of Applied Physics , Chinese Academy of Sciences , Shanghai 201800 , China.
² School of Nuclear Science and Technology , University of Chinese Academy of Sciences , Beijing 100049 , China.

PMID: 30908025
DOI: 10.1021/acs.inorgchem.9b00047

Abstract

The coordination structures of a series of uranyl-diamide complexes, namely UO₂(TMGA)₂²⁺, UO₂(TMTDA)₂²⁺, and UO₂(TMPDA)₂²⁺ (TMGA: N, N, N', N'-tetramethylglutaramide; TMTDA: N, N, N', N'-tetramethyl-3-thiodiglycolamide; TMPDA: N, N, N', N'-tetramethylpyridine-2,6-dicarboxamide), in the gas phase and solution were studied by electrospray ionization (ESI) mass spectrometry, density functional theory (DFT) calculations, and extended X-ray absorption fine structure (EXAFS) spectroscopy. ESI of UO₂Cl₂-TMGA, UO₂Cl₂-TMTDA, and UO₂Cl₂-TMPDA solutions produced UO₂(TMGA)₂²⁺, UO₂(TMTDA)₂²⁺, and UO₂(TMPDA)₂²⁺ as the major complexes in the gas phase. The gas-phase fragmentation patterns of these three complexes upon collision-induced dissociation (CID) are quite similar, and the products arising from (CH₃)₂N-CO_carbonyl, CH₂-CO_carbonyl, C_pyridine-CO_carbonyl, and CH₂-CH₂/S bond cleavages were identified, which agree with the degradation patterns of diamides upon γ irradiation in solution. DFT calculations revealed similar bidentate coordination modes of TMGA and TMTDA in the UO₂(TMGA)₂²⁺ and UO₂(TMTDA)₂²⁺ complexes in the gas phase. For UO₂(TMPDA)₂²⁺, UO₂²⁺ is coordinated by two O_carbonyl and one N_pyridine from each TMPDA, which acts as a tridentate ligand. The results from EXAFS analysis indicate that the coordination structures of UO₂(TMGA)₂²⁺, UO₂(TMTDA)₂²⁺, and UO₂(TMPDA)₂²⁺ in solution are similar to those in the gas phase.