The reaction of some tertiary phosphines with two mole equivalents of diiodine to produce the iodophosphonium triiodides [R3PI]I3; influence of R in causing subtle variations in solid state structures

Abstract

A variety of R₃PI₄ compounds have been synthesized and characterised by elemental analysis, NMR and visible spectroscopy. Apart from Ph₃PI₄, all are reported for the first time. X-Ray crystallographic studies on two of these materials, Prⁱ₃PI₄ and (Prⁿ₂N)₃PI₄, revealed different solid-state structures which are, in turn, different to both the two polymorphs of Ph₃PI₄ and Fc₃PI₄ (Fc = ferrocenyl) the crystal structures of which have been previously reported. The compound Prⁱ₃PI₄ exists as [(IPPrⁱ₃)₂I₃]I₃, which contains two [IPPrⁱ₃]⁺ cations independently weakly linked to one of the two terminal iodine atoms of the same triiodide anion. The structure also contains a discrete triiodide anion. The compound (Prⁿ₂N)₃PI₄ exhibits very little anion–cation interaction. Of the two molecules present in the asymmetric unit, one exhibits no anion–cation interaction, while the other shows only a very weak contact [d(I–I)] (cation–anion) = 3.944(2) Å.