The reaction of uranyl and lanthanide nitrates with cucurbit[6]uril (CB6) in the presence of perrhenic acid and under hydrothermal conditions yields the novel heterometallic uranyl-lanthanide molecular complexes [UO(2)Ln(CB6)(ReO4)(2)(NO3)(H2O)(7)](ReO4)(2) (Ln = Sm, Eu, Gd, Lu). Both metal cations are bound to carbonyl groups of the same CB6 portal, one for UO22+ and two for Ln(3+). The uranium atom is also bound to one monodentate perrhenate ion and three aquo ligands, while the lanthanide is bound to one monodentate perrhenate and one nitrate ions, and four aquo ligands. Not only are these complexes rare examples of ReO4- bonding to f element ions, but the perrhenate bound to Ln is included in the CB6 cavity, thus providing the first case of inclusion of a tetrahedral oxoanion in this macrocycle.