Phosphorus pentaiodide is a hypothetical inorganic compound with formula PI5.

The existence of this compound has been claimed intermittently since the early 1900s.

[3] 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.

This cation is known with the anions tetraiodoaluminate [AlI4]−, hexafluoroarsenate [AsF6]−, hexafluoroantimonate [SbF6]− and tetraiodogallate [GaI4]−.

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