Gas-phase coordination complexes of multiply-charged metal cations provide opportunities to probe fundamental properties of metal complexes in the absence of perturbations due to solvent or lattice, and with the ability to isolate and interrogate specific discrete ions. An effective technique for producing cation complexes is electrospray ionization (ESI), whereby a ligated metal ion is transferred from solution to gas. There are many reports of dipositive metal ions from solution to gas by ESI, fewer examples of tripositives, and heretofore no tetrapositive metal ions by ESI. As the metal ion charge increases, the probability of survival from solution to gas diminishes due to Coulomb explosion of the complex to reduced charged fragments; highly charged metal ions are furthermore susceptible to gas-phase ion-molecule reactions such as hydrolysis. By employing a strongly complexing and protective tridentate oxygen-donor ligand, L, we have employed ESI to produce stable gas-phase tetrapositive metal ion complexes An(L)34+, where An = Th, U, Np or Pu. Fragmentation and charge-reduction of these and other multiply charged cations by collision induced dissociation and electron transfer dissociation reveal underlying aspects of metal ion chemistry, including variations across the actinide series for the tetravalent An4+ ions. Computational studies provide insights into the structures and bonding in multiply charged metal ion complexes, and their fragmentation/reduction patterns. Gas-phase behavior of metal ion complexes parallels that in condensed phase; solution chemistry can be elucidated by this type of gas-phase experiment and theory.

Formation and chemistry of multiply-charged gas-phase actinide cation complexes

247th National Meeting (2014)

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