Laser Ablation Synthesis of Lanthanide Oxide Cluster Ions Incorporating a Heterovalent Metal

Lanthanide (Ln) oxide cluster ions produced directly by excimer laser ablation of oxalates into vacuum were investigated by time-of-flight mass spectrometry. Whereas previous studies in our laboratory identified pure Ln m O n + and mixed Ln m 1 Ln‘ m 2 O n +, the present work focused on analogous clusters incorporating an alkaline earth (A) or transition (T) metal: {Ln m O n · p AO} + and {Ln m O n ·TO 2 } + (Ln = La, Tb, Ho or Yb; A = Ca or Sr; T = Ta, Zr, or Hf). The formation of atomically combined clusters from physical mixtures of a solid lanthanide oxalate with a heterovalent metal oxide supports gas-phase coalescence as the dominant formation mechanism (vs direct cluster ejection). The stoichiometries and abundance distributions of the bimetallic oxide cluster ions are interpreted in the context of their chemical and structural constitutions. Ion abundance maxima for {LnO·3AO} + are consistent with an ionically bonded cuboid microlattice; this cubic structure type may also pertain to related binary Ln m O n + . Distinctive abundances (stabilities) of such compositions as {Ln 3 O 4 ·2AO} + and {Ln 5 O 7 ·AO} + suggest similar cuboid structures there. It was found that ZrO 2 and HfO 2 formed adducts with oxidatively saturated binary Ln m O n + which had been identified previously, producing new bimetallic oxide clusters. In contrast, Ta(V) incorporation was found to result in entirely novel cluster stoichiometries. Apparently, ZrO 2 /HfO 2 ionically coordinates intrinsically stable Ln m O n +, whereas Ta(V) induces singular cluster ions which incorporate Ta−O−Ln bonding. No binary A m O n + or T m O n + cluster ions were observed, emphasizing the distinctive stability of lanthanide oxide clusters.