Bis(imido) uranium(VI) trans- and cis-dichalcogenate complexes with the general formula U((NBu)-Bu-t)(2)(EAr)(2)(OPPh3)(2) (EAr = O-2-(BuC6H4)-Bu-t, SPh, SePh, TePh) and U((NBu)-Bu-t)(2)(EAr)(2)(R(2)bpy) (EAr = SPh, SePh, TePh) (R(2)bpy = 4,4'-disubstituted-2,2'-bipyridyl, R = Me, Bu-t) have been prepared. This family of complexes includes the first reported monodentate selenolate and tellurolate complexes of uranium(VI). Density functional theory calculations show that covalent interactions in the U-E bond increase in the trans-dichalcogenate series U(NtBu)(2)(EAr)(2)(OPPh3)(2) as the size of the chalcogenate donor increases and that both 5f and 6d orbital participation is important in the M-E bonds of U-S, U-Se, and U-Te complexes.