The structure of triphenylphosphorus–diiodine, Ph 3 PI 2 , the first crystallographically characterised dihalogen derivative of a tertiary phosphine

Triphenylphosphine reacts with diiodine in dry diethyl ether to produce Ph3PI2, shown by X-ray crystallography to be a molecular four-coordinate compound Ph3P–I–I, and not the five-coordinate Ph3PI2 or the ionic [Ph3PI]+I–, previously thought to be the only possible solid-state structures for such a compound.