Investigation of Uranyl Nitrate Ion Pairs Complexed with Amide Ligands using Electrospray Ionization Ion Trap Mass Spectrometry and Density Functional Theory
Ion populations formed from electrospray of uranyl nitrate solutions containing different amides vary depending on ligand nucleophilicity and steric crowding at the metal center. The most abundant species were ion pair complexes having the general formula [UO2(NO3)(amide)n=2,3]+, and complexes containing the amide conjugate base, reduced uranyl UO2+, and a 2+ charge were also formed. The formamide experiment produced the greatest diversity of species that stems from weaker amide binding leading to dissociation and subsequent solvent coordination or metal reduction. Experiments using methyl formamide, dimethyl formamide, acetamide, and methyl acetamide produced ion pair and doubly charged complexes that were more abundant, and less abundant complexes containing solvent or reduced uranyl. This pattern is reversed in the dimethylacetamide experiment, which displayed reduced doubly charged complexes and augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that inter-ligand repulsion distorts the amide ligands out of the uranyl equatorial plane, and that complex stabilities do not increase with increasing amide nucleophilicity. Elimination of an amide ligand largely relieves the interligand repulsion, and the remaining amide ligands become closely aligned with the equatorial plane in the structures of the bis-amide ligands. The studies show that the phenomenological distribution of coordination complexes in a metal-ligand electrospray experiment is a function of both ligand nucleophilicity and interligand repulsion, and that the latter factor begins exerting influence even in the case of relatively small ligands like the substituted methyl-formamide and –acetamide ligands.
- Research Organization:
- Idaho National Laboratory (INL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC07-05ID14517
- OSTI ID:
- 1020284
- Report Number(s):
- INL/JOU-10-20093
- Journal Information:
- Journal of Physical Chemistry A, Journal Name: Journal of Physical Chemistry A Journal Issue: 15 Vol. 115
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACETAMIDE
AMIDES
DISSOCIATION
DISTRIBUTION
FORMAMIDE
FUNCTIONALS
ION PAIRS
IONIZATION
MASS SPECTROSCOPY
SOLVENTS
URANYL COMPLEXES
URANYL NITRATES
amide
coordination complex
density functional theory
electrospray ionization
mass spectrometry
uranium
uranyl