Experimental and computational investigation of the intrinsic reactions of [UIVF2(CCH)]+: formation of [UIVF2(O2CR)]+, [UIVF(O2CR)2]+, & [UIV(O2CR)3]+ by reactions with carboxylic acids

Abstract

While there is extensive literature on the intrinsic reactions of gas-phase ions containing, for example, U^I, U^II and U^VI, there is far less information about species with the element in middle oxidation states such as U^III and U^IV. This is in part due to the difficulty in preparing such species in the gas phase. We report here the first of a series of studies we have conducted to probe the gas-phase reactivity of a formally U^IV species, [UF₂(CCH)]⁺ created from a U^VI precursor using a preparative tandem mass spectrometry. The [UF₂(CCH)]⁺ ion was isolated in a quadrupole ion trap mass spectrometer modified to allow the investigation of ion-molecule reactions. Ion-molecule reactions between [UF₂(CCH)]⁺ and formic, acetic, propionic, and acrylic acid (independently) caused elimination of HCCH and/or HF to create a series of formally U^IV carboxylate species with general formula [UF_n(O₂CR)_m]⁺ (n = 0, 1, 2 and m = 1, 2, 3). To the best of our knowledge, this is the first reported synthesis in the gas phase of these types of species. The reactions which produce the new carboxylate ions were explored using density functional theory calculations, and computed reaction energies are in good agreement with the experimentally derived ion-molecule reaction mass spectra.