Highly porous uranyl compounds in which SO₄^2- or SeO₄^2- ions link adjacent U centers were prepared by using a crown ether as template. The uranyl sulfate (see picture; U- and S-centered polyhedra are yellow and green, respectively) has the lowest density so far reported for actinide oxide frameworks, while the uranyl selenate forms tubules that are separated by columns of [(H₃O)@([18]crown-6)]⁺ complex cations. (Figure Presented)