in which the central atom exhibits a high coordination number. The other larger halide ions show this tendency to a greatly diminished extent and the complexes formed are usually less stable,although certain metals (e.g. mercury) from iodo-complexes,for example which are more stable than fluoro- or chloro- complexes.In certain cases there is insufficient space around the atom for as many iodine atoms as for other halogens, for example phosphorus forms pentahalides with fluorine,chlorine and bromine (and in the case of fluorine the ion,but no pentaiodine.The large size of iodine also accounts for the fact that there are few complexes with more than four iodine ligands.