Actinide Gas-Phase Chemistry:  Reactions of An⁺ and AnO⁺ [An = Th, U, Np, Pu, Am] with Nitriles and Butylamine

Abstract

Laser ablation with prompt reaction and detection was applied to study gas-phase reactions of actinide ions, An+ and AnO+ [An = Th, U, Pu, Np, Am], with nitriles and butylamine; Tb and Tm were included for comparison. Particular emphasis was on Np and Am as this is the region of the An series where a transition to Ln-like character is manifested. A goal was to assess the role of the coordinating N: site on actinide ion−molecule interactions. The results for the nitriles were generally reminiscent of those for reactions with alkenes and the inert character of Pu+ and Am+ with regard to dehydrogenation, despite adduct formation, indicated that C−H activation requires two non-5f electrons to produce a C−An+−H complex. With the butyronitriles and valeronitrile, Am+ produced AmC2H4 +, possibly via an “ion/dipole” interaction. Most MO+ exhibited only adduct formation with the nitriles although ThO+ was distinctively reactive, consistent with a description of Th as a quasi-d-block element. Both Np+ and Tb+ were substantially effective at dehydrogenating butylamine and Am+ exhibited a lesser degree of reactivity. Reactions of the MO+, TbO+, NpO+, and AmO+ with butylamine revealed a dramatic effect of oxo-ligation: AmO+ was at least as reactive as TbO+ and NpO+. It is postulated that the MO+ reactions proceeded via a multicentered intermediate without insertion into a C−H bond. Bis-complexes were produced with nitriles and butylamine, attesting to strong complexation with the :N functionality. An ancillary discovery was Am2 +−An dimers/clusters should elucidate the nature of actinide intermetallic bonding, including the role of 5f electrons.

Berkelium and californium organometallic ions

“…Because the ablation conditions are sufficiently energetic to produce substantial amounts of M + (ionization energy of M ≈ 600 kJ mol −1 ), a substantial population of excited state M + * should also be produced in the ablation plume. The finding of primarily ground state M + is, however, consistent with the results of metal ion -molecule reactions carried out using comparable ablation conditions [9][10][11][12][13][14]. We therefore postulate that the dominant M + /R association processes occur after partial expansion and concomitant cooling of the ablation plume.…”

“…Because significant amounts of oxide cluster ions do not generally appear upon ablation of binary actinide oxides [9][10][11][12][13][14], it is presumed that the clusters observed in the present study resulted from coalescence in the dense ablation plume by reactions such as: AnO + + AnO → An 2 O 2 + . The Cf 2 O + may have resulted from combination of Cf + and CfO, consistent with the tendency of Cf to exhibit reduced oxidation states and the dearth of CfO + .…”

“…A "monovalent" An + can readily form a single covalent bond, and a "divalent" An + two such bonds. For the gas-phase transuranium actinide ions, it has been established that the quasi-valence 5 f electrons are sufficiently localized and energetically "anchored" to the closed-core Rn nuclear/electronic assembly ([Rn]) that they do not actively participate in organometallic bonding [10][11][12][13][14]. The ground state electronic configurations of the free An + ions, Np + through Cf + , are [Rn]5 f n−1 7s 1 , with an exception being Cm + .…”

“…These reactions typically produce organoactinide complex ions via elimination of stable molecules such as H 2 [9][10][11][12][13][14]. The dominant products are generally well-represented as an An + electrostatically bonded to one or more unsaturated organic ligands via π-orbital interactions; none of the products were considered to involve direct σ-type bonding between the actinide and carbon.…”

Gas-phase transuranium chemistry: reactions of actinide ions with alcohols and thiols

“…As was found previously for butylamine, 37 An C and Ln C , which do not normally dehydrogenate alkanes, evidently did induce H 2 loss from the alkyl chain of propanol, to produce the -O-C 3 Several products resulting from presumably more complex, multi-step reaction mechanisms were identified, but can be only discussed speculatively. Of particular interest were the several organometallic species which evidently incorporated direct metal-carbon bonding.…”