Triaquocalcium(18-crown-6) heptaiodopentacuprate(I), triaquostrontium(18-crown-6) heptaiodopentacuprate(I), and triaquozinc(18-crown-6) heptaiodopentacuprate(I)

Ca(H₂O)₃(18-crown-6)Cu₅I₇ (I), Sr(H₂O)₃(18-crown-6)Cu₅I₇ (II), and Zn(H₂O)₃(18-crown-6)Cu₅I₇ (III) are isostructural solids with a polymeric array of Cu₅I₇ stoichiometry. The repeat unit may be understood as a distorted tetrahedron of four copper(I) atoms, bridged on two faces and three edges by iodide atoms, bridged on an additional edge by an I–Cu–I sequence and linked in polymeric series by this copper atom and one of the face-bridging iodide atoms. The three solid materials display no emission in the visible when excited in the ultraviolet. Comparison with other polymeric cuprous iodide materials that do emit suggests that the quenching of the expected emission may stem from short Cu–Cu interactions (2.4–2.5 Å) that represent a bonding interaction.