Introduction Click to copy section linkSection link copied! Complexes of high-valent uranium (>+4 oxidation state) are commonly observed in linear dioxo (uranyl, [O = Un+=O]m+, n = 5, 6; m = n–4) complexes. (1,2) Aside from uranyl complexes, several U6+ mono-oxo or -imido complexes are known, as well as neutral, pseudo-octahedral hexa-halide, alkoxide, alkyl, and amide complexes.