Addition of E (E = 0.125S(8), Se) to [Cp-2*Co][U(O)(NR2)(3)] (R = SiMe3) in THF results in the isolation of the chalcogen-substituted uranyl analogues [Cp-2*Co][U(O)(E)(NR2)(3)] [E = S (1), Se (2)] in good yields. Similarly, addition of 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to [Cp-2*Co][U(O)(NR2)(3)] affords the uranyl complex [Cp-2*Co][UO2(NR2)(3)] (3). All of the complexes were fully characterized, including analysis by X-ray crystallography. They were also analyzed by density functional theory calculations to probe the changes in the U-E bond as group 16 is descended.