Direct synthesis and electron‐ionization positive‐ion mass spectrum of tetrakis(acetylacetonato)cerium(IV), Ce(C5H7O2)4

Abstract

AbstractCrystalline Ce(C5H7O2)4 has been synthesized directly from the reaction of hydrated cerium(IV) oxide with acetylacetone, (C5H8O2), and its electron‐ionization (EI) mass spectrom is reported. The compound exists as a monomer (mass 536) in the gaseous state. The mass spectrum, like those of M(C5H7O2)4 (M = Zr or Th) and CeL4 (L = fluorinated β‐diketonate), shows the dominant ion signal to be due to the [Ce(C5H7O2)3]+ ion that arises from the loss of one C5H7O2 from the molecular ion. An internal electron‐transfer affords [Ce(C5H7O2)3]+˙. Fragmentation of [Ce(C5H7O2)3]+˙ to [Ce(C5H7O2)2]+ is similar to that observed for the tris‐chelates of trivalent transition metals and La(C5H7O2)3. The ion [Ce(C5H7O2)2]+ ultimately breaks down to [CeO]+ through the sequential loss of three even‐electron neutral species, CH3COCHCCH2, H2O and CH3COCHCCH2 without invoking any further reduction of the Ce centre. Mechanisms are given for the loss of the three even‐electron species from the bis(acetylacetonato)cerium(III) ion fragment. Theoretical simulations of patterns of the fragment ions [Ce(C5H7O2)3]+˙, [Ce(C5H7O2)2]+˙, and [Ce(C5H7O2)OH]+ have been made and compared with those of the corresponding experimental results in support of the suggested mode of fragmentation.