The reaction of some tertiary phosphines with two mole equivalents of diiodine to produce the iodophosphonium triiodides [R3PI]I-3; influence of R incausing subtle variations in solid state structures

A variety of R3PI4 compounds have been synthesized and characterised by ele mental analysis, NMR and visible spectroscopy. Apart from Ph3PI4, all are r eported for the first time. X-Ray crystallographic studies on two of these materials, (Pr3PI4)-P-i and ((Pr2N)-N-n)(3)PI4, revealed different solid-st ate structures which are, in turn, different to both the two polymorphs of Ph3PI4 and Fc(3)PI(4) (Fc = ferrocenyl) the crystal structures of which hav e been previously reported. The compound (Pr3PI4)-P-i exists as [(IPPr3i)(2 )I-3]I-3, which contains two [IPPr3i](+) cations independently weakly linke d to one of the two terminal iodine atoms of the same triiodide anion. The structure also contains a discrete triiodide anion. The compound ((Pr2N)-N- n)(3)PI4 exhibits very little anion-cation interaction. Of the two molecule s 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) Angstrom.