“…Considering existing knowledge on XI 4 type crystals [14,15,16,17,18,19] that possess a cubic symmetry, this unusual structure has been explained by the close packing of I atoms and by an intermolecular I − I bond [11]. The observed large value of the ionization potential, found by ultraviolet spectroscopy, was explained also by the presence of this bond [20]. Recently, this system was exploited as a model for packing tetrahedra [19].…”