Reduction Chemistry of Neptunium cyclopentadienide complexes: from structure to understanding

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 eta5-coordination around the NpIII centre; additionally in [Np(Cp)3] and K[Np(Cp)4] one Cp ring establishes a mu-eta1-interaction to one C atom of a neighbouring NpCp3 unit. The solid state structure of K[NpCp4] is unique in containing two different types of metal-Cp coordination geometries in the same crystal. NpIIICp4 units are found exhibiting four units of eta5-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 the putative neptunium(II) K(2.2.2 cryptand)[Np(Cp')3] that is thermally unstable above -10 °C like its U and Th congeners. 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.

DUTKIEWICZ Michal Seweryn;  APOSTOLIDIS Christos;  WALTER Olaf;  ARNOLD Polly L.; 

2017-04-10

ROYAL SOC CHEMISTRY

JRC105590

2041-6520,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC105590,   

10.1039/c7sc00034k,