Addition of the Cl ^- anions to the synthesis mixture stabilizes specific structures of uranyl complexes which results in new compounds with the unprecedented structural topologies. ((CH ₃) ₂CHNH ₃)[(UO ₂)(CrO ₄) · Cl(H ₂O)] is a new member of the small family of compounds based upon the Ur(X _mO _n) ₅ (X = Cl, Br, I) bipyramids. The structure is based upon uranyl chloride chromate layers that alternate with the layers of protonated amine molecules. The layers contain UrClO ₄ pentagonal bipyramids that share three of its equatorial corners with CrO ₄ tetrahedra. Topological analysis shows that the [(UO ₂)(CrO ₄)Cl(H ₂O)] ^- layer belongs to the same topology of interpolyhedral linkage as in a-UO ₂MoO4(H ₂O) ₂.This type of topology (linkage of 4-membered rings creating 8-membered rings) is known in silicate crystal chemistry as the topology of the [Si ₄O ₁₀] layers in the minerals of the apophyllite group. Their linkage via various intermediate units results in a large family of open-framework and pillared silicates.