Non-aqueous neptunium and plutonium redox behaviour in THF – access to a rare Np(III) synthetic precursor

Solvent exchange of NpCl₄(DME)₂ with THF proceeds simply to yield NpCl₄(THF)₃, whereas PuCl₄(DME)₂ is unstable in THF, partially decomposing to the mixed valent [Pu^IIICl₂(THF)₅][Pu^IVCl₅(THF)] salt. Reduction of NpCl₄(THF)₃ with CsC₈ ultimately afforded NpCl₃(py)₄, the only example of a structurally characterized solvated Np(III) halide. The method demonstrates a route to a well-defined Np(III) starting material without the need to employ scarcely available Np metal.