Actinide-Pnictide Chemistry: A Uranium Primary Alkyl Stibinide and a Diuranium Hexaantimonide-Tetralithium Zintl Cluster

Abstract

Structurally characterised U−Sb bonds are rare. Here, the synthesis and characterisation of [U(Tren^DMBS){Sb(H)C(H)(SiMe₃)₂}] (5, Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t)₃) and [{U(Tren^TIPS)}₂{Sb₃(μ₆-Li)(μ-Li[THF]₂)₃Sb₃}] (6, Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃) are reported. Complex 5 is an unprecedented primary stibinide actinide complex and 6 can be formulated as containing a unique triple decker 20 skeletal-electron distorted closo tricapped Zintl cluster (Sb₃Li₄Sb₃)²⁻ that is analogous to the D_3h closo tricapped trigonal prism form of [Ge₉]²⁻. Quantum chemical calculations emphasise polar U−Sb bonding in 5 and 6, and that viewing (Sb₃Li₄Sb₃)²⁻ as a single unit rather than two distinct but contiguous (Sb₃)³⁻ units, themselves unprecedented in molecular actinide chemistry, is valid due to the presence of three weak (Sb₃)⋯(Sb₃) (3, −1)-bond critical points. Complexes 5 and 6 highlight the challenges of preparing polar U−Sb bonds and the underlying tendency for unpredictable cluster formation with Sb.