High-Energy Organometallic Chemistry of Curium:  Laser Ablation of Cm₇O₁₂ Dispersed in Polyimide

Abstract

Gas-phase curium organometallic ions were synthesized by metal/polymer co-ablation. Vacuum laser ablation of a dilute dispersion of curium oxide in polyimide resulted in several organocurium ions, evidently formed by nucleation of Cm+ and various neutral polymer fragment radicals in the ablation plume. The compositions and abundances of simple species, such as CmC2 +, CmC2H+, and CmCN+, can be rationalized on the basis of the electronic structure and energetics of the curium ion, Cm+. The results for curium are in accord with a general thermochemical model previously employed to understand the organometallic speciation of preceding actinides. The identification of the above-specified species, along with several larger organocurium ions, extends the realm of organoactinide chemistry; specifically, it represents identification of a series of unique curium complexes which presumably incorporate substantially covalent (σ) Cm−C bonding. Also identified in the ablation plume were small clusters incorporating two or three curium atoms. Simple clusters, such as Cm3O4 +, reveal a trivalent, lanthanide-like character for curium and reflect the tendency toward bulk, solid-state chemical behavior upon coalescence of only a few atoms. Finally, a notable ancillary observation was the formation of several clusters in which C2 evidently substituted sequentially for an O atom, revealing the pseudo-oxygen character of the dicarbide moiety.

Berkelium and californium organometallic ions

“…Non-organometallic divalent species identified were: An + =O (oxide), and HO−An + −OH (dihydroxide). These assignments have been discussed in detail elsewhere in the context of MPCA of lighter actinides [1][2][3][4]. As expected in a plume environment with a plethora of radical fragments, bare and oxo-ligated metal ions can combine to produce additional products, as evidenced by the continuum of peaks in Fig.…”

“…2. Although the structures of the identified species cannot be positively assigned based on the MPCA mass spectra alone, it has been concluded [1][2][3][4] that the primary organoactinide ions are consistent with the formation of one or two direct An + −C covalent-type bonds of indeterminate degree of ionicity. The singly-bonded (monovalent actinide center) species are represented as An + −R 1 , and the doubly-bonded (divalent actinide) species as An + =R 2 or R 1 −An + −R 1 .…”

“…The monovalent An + ([Rn]5 f n−1 7s 1 ) possess a chemically available electron, "external" to the localized 5 f n−1 partially filled shell, which effectively combines with the radical carbon in species such as • C ≡ CH and • C ≡ N to produce complexes such as acetylides (An + −C ≡ CH) and cyanides (An + −C ≡ N). The special case of Cm + has been discussed elsewhere [4]; essentially, the ion energetics are such that nominally inert ground state of Cm + is easily excited to the monovalent state ([Rn]5 f 8 7s 1 ), only 25 kJ mol −1 higher in energy; the intrinsically inert character of the [Rn]5 f 7 7s 2 ground state not manifested in MPCA.…”

“…It has been demonstrated that a variety of gas-phase organometallic ions can be synthesized by laser ablation of a dispersion of a metal oxide in polyimide [1][2][3][4]. This metal/polymer co-ablation (MPCA) approach has been particularly effective for synthesizing new organometallic ions comprising members of the f -element lanthanide (Ln) and actinide (An) series.…”

“…This metal/polymer co-ablation (MPCA) approach has been particularly effective for synthesizing new organometallic ions comprising members of the f -element lanthanide (Ln) and actinide (An) series. Studies have been carried out with several lanthanides and the actinides: thorium and uranium [1], neptunium and plutonium [2], americium [3], and curium [4]. A specific advantage of this approach for α-emitting, transuranium nuclides is that only a milligram or less of material is needed.…”