Reduction Chemistry of Neptunium cyclopentadienide complexes: from structure to understanding

Michał Dutkiewicz, Christos Apostolidis, Olaf Walter, Polly Louise Arnold

Research output: Contribution to journalArticlepeer-review

Abstract

Neptunium complexes in the formal oxidation states II, III, and IV supported by cyclopentadienyl ligands are explored, and significant differences between Np and U highlighted as a result. A series of neptunium(III) cyclopentadienyl (Cp) complexes [Np(Cp)3], its bis-acetonitrile adduct [Np(Cp)3(NCMe)2], plus its KCp adduct K[Np(Cp)4] and [Np(Cp')3] (Cp' = C5H4SiMe3) have been made and characterised providing the first single crystal x-ray analyses of NpIII Cp complexes. In all NpCp3 derivatives there are three Cp rings in η5-coordination around the NpIII centre; additionally in [Np(Cp)3] and K[Np(Cp)4] one Cp ring establishes a μ-η1-interaction to one C atom of a neighbouring Np(Cp)3 unit. The solid state structure of K[Np(Cp)4] is unique in containing two different types of metal-Cp coordination geometries in the same crystal. NpIII(Cp)4 units are found exhibiting four units of η5-coordinated Cp rings like in the known complex [NpIV(Cp)4], the structure of which is now reported. A detailed comparison of the structures gives evidence for the change of ionic radii of ca. -8 pm associated with change in oxidation state between NpIII and NpIV. The rich redox chemistry associated with the syntheses is augmented by the reduction of [Np(Cp')3] by KC8 in the presence of 2.2.2 cryptand to afford a neptunium(II) complex that is thermally unstable above -10 °C like the UII and ThII complexes K(2.2.2 cryptand)[Th/U(Cp')3]. Together, these spontaneous and controlled redox reactions of organo-neptunium complexes, along with information from structural characterisation, show the relevance of organometallic Np chemistry to understanding fundamental structure and bonding in the minor actinides.
Original languageEnglish
JournalChemical Science
Early online date30 Jan 2017
DOIs
Publication statusE-pub ahead of print - 30 Jan 2017

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