(UO2)2[UO4(trz)2](OH)2: A U(VI) Coordination Intermediate between a Tetraoxido Core and a Uranyl Ion with Cation–Cation Interactions

A uranyl triazole (UO2)2[UO4(trz)2]­(OH)2 (1) (trz = 1,2,4-triazole) was prepared using a mild solvothermal reaction of uranyl acetate with 1,2,4-triazole. Single-crystal X-ray diffraction analysis of 1 revealed it contains sheets of uranium–oxygen polyhedra and that one of the U­(VI) cations is in an unusual coordination polyhedron that is intermediate between a tetraoxido core and a uranyl ion. This U­(VI) cation also forms cation–cation interactions (CCIs). Infrared, Raman, and XPS spectra are provided, together with a thermogravimetric analysis that demonstrates breakdown of the compound above 300 °C. The UV–vis–NIR spectrum of 1 is compared to those of another compound that has a range of U­(VI) coordination enviromments.