Because iodine is the largest, least electronegative, and most polarizable of the common halogens, it is also capable of forming stable polycoordinate high-valent (with a value of up to 7, IF7) compounds. The most common polyvalent organic iodine compounds are I(III) and I(V) species. The first stable polyvalent organic iodine compound, the trivalent PhICl2, was prepared by the German chemist C. H. C. Willgerodt in 1886.