Synthesis and Hydrolysis of Uranyl, Neptunyl, and Plutonyl Gas-Phase Complexes Exhibiting Discrete Actinide–Carbon Bonds

Abstract

Gas-phase organoactinyl complexes possessing discrete An−C bonds (An = U, Np, Pu) were synthesized in a quadrupole ion trap by endothermic decarboxylation of [AnO 2 (O 2 C−R) 3 ]− anion complexes in which a formally AnO 2 2+ actinyl core is coordinated by three carboxylate ligands, with R = CH 3 (methyl), CH 3 CC (1-propynyl), C 6 H 5 (phenyl), C 6 F 5 (pentafluorophenyl). Decarboxylation and competing ligand loss were studied computationally by density functional theory complementing experiment. Although decarboxylation was computed to be the energetically most favorable process in all cases, reduction from An(VI) to An(V) via neutral ligand loss was often prevalent, particularly for An = Np, Pu, presumably resulting from barriers associated with decarboxylation. Comparative hydrolysis rates of the An−C bonds were experimentally determined, and the chemical properties of these bonds were analyzed by the quantum theory of atoms in molecules. The measured hydrolysis rates differed by up to 3 orders of magnitude: the fastest was for [(CH 3 CC)UO 2 (O 2 C− CCCH 3 ) 2 ]− and the slowest for [(C 6 F 5 )PuO 2 (O 2 C−C 6 F 5 ) 2 ]− . There is a general correlation between hydrolysis exothermicity and hydrolysis rate. Prototypical hydrolysis reaction pathways computed for R = CH 3 (An = U, Np) reveal a mechanism in which an outer-sphere water becomes inner-sphere concomitant with transfer of an H atom to yield an OH ligand and CH 4 , with a net energy release of 170 kJ mol −1 and a transition state barrier of 45 kJ mol −1 for An = U. Infrared multiphoton dissociation spectra of selected complexes were acquired to confirm the predicted structures by agreement between the computed and observed vibrational frequencies. The experiment and theory results provide an evaluation of the comparative propensities for formation of the organoactinyls as a function of actinide and carboxylate and an assessment of the nature and stability toward hydrolysis of the primarily ionic An−C bonds.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

“…The m/z 388 product is, therefore, generated by a dissociation reaction that involves elimination of acetyloxyl radical, CH 3 -at the MS/MS stage are consistent with earlier CID studies [26,30], including an investigation of decarboxylation and synthesis of organometallic actinide (An) species performed using a 3-D quadrupole ion trap [26]. …”

“…More , had previously been prepared in a Bbottom-up^approach by insertion of U + into NO in an ion-molecule reaction [28], our experiments demonstrated that the species can also be created in a CID reaction. Formation of the nitrido species by transfer of N from cyanide was confirmed using precursors labeled with -in a 3-D quadrupole ion trap has been reported [26,30], and the structure of the species has been determined using infrared multiple-photon photodissociation (IRMPD) spectroscopy [31]. However, the experiments reported here demonstrate that the chemistry of product ions from both systems can be explored more accurately in the 2-D LIT.…”

Revealing Disparate Chemistries of Protactinium and Uranium. Synthesis of the Molecular Uranium Tetroxide Anion, UO4–

“…The IRMPD spectra were acquired using a QIT/MS similar to that previously employed to study uranyl-crown and organouranyl complexes. 39,40 The QIT/MS has been modified 41,42 such that the high-intensity tunable IR beam from FELIX can be directed onto the ion packet, resulting in multiphoton dissociation that is appreciable only when the IR frequency is resonant with a sufficiently intense absorption vibrational mode of the particular mass-selected complex being studied. The FEL produces ∼5 μs long IR pulses with an energy of ∼40 mJ/pulse at a repetition rate of 10 Hz.…”

Electronic structure theory to decipher the chemical bonding in actinide systems

“…As an illustrative example, we consider the gas-phase organoactinyl complexes possessing discrete An -C bonds (An = U, Np, Pu) recently synthesized by Dau et al [57] in a quadrupole ion trap by endothermic decarboxylation of [AnO 2 (O 2 C -R) 3 ] -anion complexes. A formally AnO 2 2+ actinyl core is coordinated by three carboxylate ligands, with R= CH 3 (methyl), CH 3 CC (1-propynyl), C 6 H 5 (phenyl), C 6 F 5 (pentafluorophenyl).…”

“…A formally AnO 2 2+ actinyl core is coordinated by three carboxylate ligands, with R= CH 3 (methyl), CH 3 CC (1-propynyl), C 6 H 5 (phenyl), C 6 F 5 (pentafluorophenyl). The chemical properties of these bonds were analysed by QTAIM [57]. Here, we calculate the partial atomic charges for the decarboxylation products, [(R)AnO 2 (O 2 C -R) 2 ] -with R = CH 3 and An=U.…”