Phosphorus pentaiodide

"PI5" redirects here; not to be confused with Pi5.

Phosphorus pentaiodide is a hypothetical inorganic compound with formula PI₅. The existence of this compound has been claimed intermittently since the early 1900s.^[2] The claim is disputed: "The pentaiodide does not exist (except perhaps as PI₃·I₂, but certainly not as [PI₄]⁺I⁻...)".^[3]

Phosphorus pentaiodide

Names
IUPAC name Phosphorus(V) iodide
Other names Pentaiodophosphorane Pentaiodophosphorus Phosphorus pentaiodide Tetraiodophosphonium iodide
Identifiers
CAS Number	66656-29-9 N
3D model (JSmol)	Interactive image
ChemSpider	10459963
PubChem CID	12617301
CompTox Dashboard (EPA)	DTXSID30504485
InChI InChI=1S/I5P/c1-6(2,3,4)5 Key: NCCBCEHAGCSKEA-UHFFFAOYSA-N
SMILES P(I)(I)(I)(I)I
Properties
Chemical formula	PI5
Molar mass	665.49611 g·mol−1
Appearance	Brown-black crystalline solid (disputed)[1]
Melting point	41 °C (106 °F; 314 K) (disputed)[1]
Related compounds
Related compounds	Phosphorus pentafluoride Phosphorus pentachloride Phosphorus pentabromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Claims

Phosphorus pentaiodide was reported to be a brown-black crystalline solid melting at 41 °C produced by the reaction of lithium iodide and phosphorus pentachloride in methyl iodide, however, this claim is disputed and probably generated a mixture of phosphorus triiodide and iodine.^[1][4]

Although phosphorus pentaiodide has been claimed to exist in the form of [PI₄]⁺I⁻ (tetraiodophosphonium iodide), experimental and theoretical data refutes this claim.^[5][1]

Derivatives

Unlike the elusive PI₅, the [PI₄]⁺ cation (tetraiodophosphonium cation) is widely known. This cation is known with the anions tetraiodoaluminate [AlI₄]⁻, hexafluoroarsenate [AsF₆]⁻, hexafluoroantimonate [SbF₆]⁻ and tetraiodogallate [GaI₄]⁻. ^[4][5]