The
coordination structures of a series of uranyl–diamide complexes,
namely UO2(TMGA)2
2+, UO2(TMTDA)2
2+, and UO2(TMPDA)2
2+ (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)2
2+,
UO2(TMTDA)2
2+, and UO2(TMPDA)2
2+ 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–COcarbonyl, CH2–COcarbonyl, Cpyridine–COcarbonyl, 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)2
2+ and UO2(TMTDA)2
2+ complexes in the gas phase. For
UO2(TMPDA)2
2+, UO2
2+ is coordinated by two Ocarbonyl and one Npyridine from each TMPDA, which acts as a tridentate ligand.
The results from EXAFS analysis indicate that the coordination structures
of UO2(TMGA)2
2+, UO2(TMTDA)2
2+, and UO2(TMPDA)2
2+ in solution are similar to those in the gas phase.