Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

Reaction of K(DME)]Th{N(R)(SiMe₂CH₂)}₂(NR₂)] (R = SiMe₃) with 1 equiv. of U(NR₂)₃(NH₂)] (1) in THF, in the presence of 18-crown-6, results in formation of a bridged uranium–thorium nitride complex, K(18-crown-6)(THF)₂](NR₂)₃U^IV(μ-N)Th^IV(NR₂)₃] (2), which can be isolated in 48% yield after work-up. Complex 2 is the first isolable molecular mixed-actinide nitride complex. Also formed in the reaction is the methylene-bridged mixed-actinide nitride, K(18-crown-6)]K(18-crown-6)(Et₂O)₂](NR₂)₂U(μ-N)(μ–κ²-C,N–CH₂SiMe₂NR)Th(NR₂)₂]₂ (3), which can be isolated in 34% yield after work-up. Complex 3 is likely generated by deprotonation of a methyl group in 2 by NR₂]⁻, yielding the new μ-CH₂ moiety and HNR₂. Reaction of 2 with 0.5 equiv. of I₂ results in formation of a U^V/Th^IV bridged nitride, (NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (4), which can be isolated in 42% yield after work-up. The electronic structure of 4 was analyzed with EPR spectroscopy, SQUID magnetometry, and NIR-visible spectroscopy. This analysis demonstrated that the energies of 5f orbitals of 4 are largely determined by the strong ligand field exerted by the nitride ligand.

The heterobimetallic actinide nitride (NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (R = SiMe₃) has an m_J = 5/2 ground state and its highest energy 5f excited state is primarily 5f-N_nitride σ-antibonding in character.