Nitrogen-rich Compounds of the Actinoids: Dioxouranium(VI) 5,5′-Azobis[tetrazolide] Pentahydrate and Its Unusually Small Uranyl Angle

Uranyl­(VI) 5,5′-azobis­[tetrazolide] pentahydrate
was synthesized
and characterized using X-ray crystallography, elemental analysis,
UV/vis, MIR, FIR, and Raman spectroscopy. It is the second-most nitrogen
rich compound of uranium (26.72 wt % N) and only the second structurally
characterized uranium complex with a tetrazole ligand described in
the literature. The compound’s structure is characterized by
an exceptionally small uranyl angle of 172.4(1)°, which provides
information on the coordination properties of tetrazole ligands as
they affect the donor’s environment by strong steric and perhaps
electrostatic repulsion. The compound showed luminescence under excitation
with a near UV laser. The mean lifetime of its excited state was shorter
than in the case of UO2(NO3)2·6H2O, indicating quenching by the ligand. Despite its high nitrogen
content (and thus potentially explosive character), the title compound
proved to be stable even under neutron radiation causing induced fission
processes.