Absorption correction: multi-scan

R factor = 0.023; wR factor = 0.053; data-to-parameter ratio = 39.3. The asymmetric unit of the title salt, C6H20N4 2+2I, comprises half a 3,6-diazaoctane-1,8-diaminium dication plus an I anion. The dications are symmetrical and lie across crystal-lographic centres of inversion. In the crystal, the ions form a network involving mainly weak N—H I intermolecular interactions: two H atoms of the ammonium group form interactions with two I anions and the H atom of the secondary amine forms a weak interaction with a third I cation. The third ammonium H atom is hydrogen bonded to a secondary amine of an adjacent cation. The backbone of the cation does not form a uniformly trans chain, but is ‘kinked’ [C—N—C—C torsion angle = 71.5 (2)], probably to accom-modate the direct hydrogen bond between the ammonium group and the secondary amine in an adjacent cation. Related literature For the structure of a dihydrate of the title compound, toge-ther with its isostructural Cl and Br analogues, see Ilioudis et al. (2000)