Metal ion-molecule reactions of Bk+: comparison with Pu+ and Tb+

Gas-phase reactions of the bare monopositive berkelium ion, Bk+, with several reagents were examined by a mass spectrometric technique adapted for the highly radioactive transuranium actinides. The earlier actinide ion, Pu+, and the homologous lanthanide ion, Tb+, were studied simultaneously to enable effective interpretation of the results in the context of the electronic structure and energetics of berkelium. Reactions with several alkenes, as well as butylamine and butyronitrile, revealed that the metal-ion mediated dehydrogenation efficiency decreased in the order: Tb+ > Pu+ > Bk+. The products included (π-bonded) organoberkelium products such as BkC8H8+, presumably the berkeliumcyclooctadienylide ''half-sandwich'' complex ion. The reactivity results are consistent with C-H activation by metal ion insertion to form C-M+-H activation complexes, and indicate that the a 5 f electron of ground state Bk+ must be promoted to a 6d orbital to provide two non-5 f valence electrons for the two covalent bonds in these σ-bonded organoberkelium intermediates. Reactions of Bk+ with hexafluoropropene, dimethylether and methylvinylether also indicated lower reactivities compared with Pu+ and Tb+. Products included berkelium alkoxide and fluoride molecular ions. The experiments reported here are an extension of a systematic study of gas-phase actinide ion chemistry, with Bk-249 now being the shortest-lived isotope for which such studies have been carried out (half-life = 320 days). The results are in accord with those for more reactive Cm+ and less reactive Cf+, which indicated essentially lanthanide-like behavior in this region of the actinide series and chemically inert (localized) 5 f electrons. Large differences between the gas-phase chemistries of Bk+ and Tb+ reflect substantial discrepancies between the electronic energetics of homologous members of the two series, consistent with spectroscopic measurements. Bond dissociation energies, BDE[M+-O], of 655 and 610 kJ mol-1 were for estimated for PuO+ and BkO+, respectively. (orig.)