Synthesis of Non-Aqueous Neptunium(III) Halide Solvates from NpO2

Lewis base adducts of NpCl4

Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl4(DME)2. Using acetonitrile and pyridine, NpCl4(MeCN)4 (1) and NpCl4(pyr)4 (2) were isolated, respectively. Addition of t-butylbipyridine and triphenylphosphine oxide generated the respective Lewis base adducts, NpCl4(tBuBipy)2 (3) and NpCl4(OPPh3)2 (4). All species were fully characterized using spectroscopic and structural analyses.

Expanding Transuranium Organoactinide Chemistry: Synthesis and Characterization of (Cp'3M)2(μ-4,4'-bpy) (M = Ce, Np, Pu)

Dinuclear, organometallic, transuranium compounds, (Cp'₃M)₂(μ-4,4'-bpy) (Cp'^- = trimethylsilylcyclopentadienide, 4,4'-bpy = 4,4'-bipyridine, M = Ce, Np, Pu), reported herein provide a rare opportunity to probe the nature of actinide-carbon bonding. Significant splitting of the f-f transitions results from the unusual coordination environment in these complexes and leads to electronic properties that are currently restricted to organoactinide systems. Structural and spectroscopic characterization in the solid state and in solution for (Cp'₃M)₂(μ-4,4'-bpy) (M = Np, Pu) are reported, and their structural metrics are compared to a cerium analogue.

Neptunium Alkoxide Chemistry: Expanding Alkoxides to the Transuranium Elements

Two oxo-containing neptunium(IV) tert-butoxides, [Np₃O(O^tBu)₁₀] (1) and [K₄Np₂O(O^tBu)₁₀] (2), were synthesized using the ligand substitution between neptunium(IV) silylamides and HO^tBu, whereas the salt metathesis between [NpCl₄(DME)₂] (DME = dimethoxyethane) and various amounts of LiO^tBu resulted in the formation of oxo-free alkoxides [Np(O^tBu)₄(py)₂] (3; py = pyridine) and [Li(THF)]₂[Np(O^tBu)₆] (4; THF = tetrahydrofuran). These complexes are the first structurally characterized neptunium(IV) alkoxides using single-crystal X-ray diffraction and solid-state absorption spectroscopy, which provide data for the development of anhydrous metal-organic neptunium chemistry.

[AnI3(THF)4] (An = Np, Pu) Preparation Bypassing An0 Metal Precursors: Access to Np3+/Pu3+ Nonaqueous and Organometallic Complexes

Direct comparison of homologous molecules provides a foundation from which to elucidate both subtle and patent changes in reactivity patterns, redox processes, and bonding properties across a series of elements. While trivalent molecular U chemistry is richly developed, analogous Np or Pu research has long been hindered by synthetic routes often requiring scarcely available metallic-phase source material, high-temperature solid-state reactions producing poorly soluble binary halides, or the use of pyrophoric reagents. The development of routes to nonaqueous Np³⁺/Pu³⁺ from widely available precursors can potentially transform the scope and pace of research into actinide periodicity. Here, aqueous stocks of An⁴⁺ (An = Np, Pu) are dehydrated to well-defined [AnCl₄(DME)₂] (DME = 1,2-dimethoxyethane), and then a single-step halide exchange/reduction employing Me₃SiI produces [AnI₃(THF)₄] (THF = tetrahydrofuran) in a high to nearly quantitative crystalline yield (with I₂ and Me₃SiCl as easily removed byproducts). We demonstrate the synthetic utility of these An-iodide molecules, prepared by metal⁰-free routes, through characterization of archetypal complexes including the tris-silylamide, [Np{N(SiMe₃)₂}₃], and bent metallocenes, [An(C₅Me₅)₂(I)(THF)] (An = Np, Pu)─chosen because both motifs are ubiquitous in Th, U, and lanthanide research. The synthesis of [Np{N(Se═PPh₂)₂}₃] is also reported, completing an isomorphous series that now extends from U to Am and is the first characterized Np³⁺-Se bond.