Bis(isopropyltriphenylphosphonium) di-μ-iodido-bis[iodidocopper(I)]

The title compound, (C21H22P)2[Cu2I4], prepared from reaction between copper powder, iodine and isopropyl triphenylphosphonium iodide in hydroxyacetone (acetol), shows an already known Cu2I4 2− anion with a planar conformation [Cu—I range = 2.5108 (3)–2.5844 (3) Å and I—Cu—I range = 110.821 (10)–125.401 (10)°].

Financial support from the Swedish Research Council is gratefully acknowledged.

Comment
Copper halide complexes have been of great interested due to their wide structural variation. The copper atoms can be in trigonal or tetrahedral geometry and this is the main reason for so many structure variations.
A search in Cambridge Structural Database shows 20 different structures containing [Cu 2 I 4 ] 2as the anion, the major difference between these are that different cations are employed in the structures. [Cu 2 I 4 ] -2 unit can be in two different forms, planar or bent.
By reacting copper powder, iodine and isopropyltriphenylphosphonium iodide in hydoxyacetone under nitrogen atmosphere and reflux colorless parallelepiped crystals are formed. X-ray crystallography shows that the mentioned crystals contain the well known [Cu 2 I 4 ] 2as the anion and isopropyltriphenylphosphonium as the cation.
The anion shows some variation in the Cu-I distance 2.5108 (3)

Experimental
Isopropyl triphenylphosphonium iodide (2.711 mmol), iodine (5.011 mmol) and copper powder (20.056 mmol) were mixed and heated under reflux in hydroxyacetone (50 ml) under a nitrogen atmosphere. After 3 hours the solution became pale yellow. The mixture was filtered while hot and solution was kept at 6°C. Well shaped parallelepiped crystals formed over the course of several days.

Refinement
The structures were solved by charge-flipping, giving the I, Cu, P and main part of the C positions. The remaining C positions were found using difference Fourier analysis. All non-hydrogen positions were refined using full matrix least squares. The hydrogen atoms were located by geometrical methods and were allowed to ride, with C-H = 1.00Å and U eq = 1.2U iso (C).
supplementary materials sup-2 Figures   Fig. 1. Molecular structure and atom-labelling scheme for the anion and cation respectively in (I). Non-H atoms are shown as 50% probability displacement ellipsoids.