The treatment of dilute aqueous solutions of [hydroxy(tosyloxy)iodo]benzene with aqueous Mg(ClO4)(2) produced thin elongated-hexagonal plates exhibiting a supramolecular structure in which tetra-mu-oxopentaiodanyl dication repeat units are joined to each other by significantly ionic bonds and each unit is associated with two perchlorate ions. The linearly extended cationic structure is formed from the 12-atom hexagonal rings of alternating iodine and oxygen atoms, a novel structure. Each 12-membered ring forms a nearly planar hexagonal shape with sides defined by almost linear O-I-O segments (175.7 +/- 1.6)degrees. The apexes are occupied by bridging oxide ligands where the I-O-I angles deviate only slightly from an ideal 120 degrees hexagonal angle (116.8 +/- 1.2)degrees, consistent with sp(2) hybridization of the bridging oxygen atoms that participate in three-center four-electron bonds with iodine. These 12-atom hexagons are slightly "chair" distorted at the oxygen atoms. The planes of the rings are separated by layers containing the phenyl rings. The perchlorate ions reside in void spaces created by the three-up, three-down arrangement of the phenyl rings around each 12-membered I-O ring and are positioned directly above and below the I-O rings.