The iodide-containing layered double hydroxides (LDHs) of Mg and Zn with Al crystallize by the inclusion of extensive positional disorder of I(-) ions in the interlayer region. I(-) ion given its poor charge to size ratio can neither screen effectively the positive charge nor participate in H-bonding with the metal hydroxide layers. Thereby the I(-) ions are not stabilized in sites close to the seat of positive charge of the metal hydroxide layers (6c), nor in sites that facilitate H-bonding (3b or 18h). On the other hand, OH(-) from water can do both and effectively displaces I(-) from the interlayer.