The anhydrous material crystallizes in the CdCl motif, featuring octahedral coordination geometry at each Ni(II) center. NiI is prepared by dehydration of the pentahydrate.
NiI readily hydrates, and the hydrated form can be prepared by dissolution of nickel oxide, hydroxide, or carbonate in hydroiodic acid. The anhydrous form can be produced by treating powdered nickel with iodine.