Carbon–sulfur bond strength in methanesulfinate and benzenesulfinate ligands directs decomposition of Np(v) and Pu(v) coordination complexes. Issue 10 (26th February 2020) - Vallet, Valérie
Abstract : Adjusting intra-ligand bond strengths in actinide sulfinate complexes directs towards alternative cleavage of carbon–sulfur or actinide–sulfinate bonds. Abstract : Gas-phase coordination complexes of actinyl(v ) cations, AnO2 +, provide a basis to assess fundamental aspects of actinide chemistry. Electrospray ionization of solutions containing an actinyl cation and sulfonate anion CH3 SO2 − or C6 H5 SO2 − generated complexes [(An V O2 )(CH3 SO2 )2 ] − or [(An V O2 )(C6 H5 SO2 )2 ] − where An = Np or Pu. Collision induced dissociation resulted in C–S bond cleavage for methanesulfinate to yield [(An V O2 )(CH3 SO2 )(SO2 )] −, whereas hydrolytic ligand elimination occurred for benzenesulfinate to yield [(An V O2 )(C6 H5 SO2 )(OH)] − . These different fragmentation pathways are attributed to a stronger C6 H5 -SO2 − versus CH3 -SO2 − bond, which was confirmed for both the bare and coordinating sulfinate anions by energies computed using a relativistic multireference perturbative approach (XMS-CASPT2 with spin–orbit coupling). The results demonstrate shutting off a ligand fragmentation channel by increasing the strength of a particular bond, here a sulfinate C–S bond. The [(An V O2 )(CH3 SO2 )(SO2 )] − complexes produced by CID spontaneously react with O2 to eliminate SO2, yielding [(AnO2 )(CH3 SO2 )(O2 )] −, a process previously reported for An = U and found here for An = Np and Pu. Computations confirm that the O2 /SO2 displacement reactions should be exothermic or thermoneutral for all three An, as was experimentally established. The computations furthermore reveal that the products are superoxides [(An V O2 )(CH3 SO2 )(O2 )] − for An = Np and Pu, but peroxide [(U VI O2 )(CH3 SO2 )(O2 )] − . Distinctive reduction of O2 − to O2 2− concomitant with oxidation of U(v ) to U(vi ) reflects the relatively higher stability of hexavalent uranium versus neptunium and plutonium.