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Gallium triiodide can be reduced with gallium metal to give a green-colored solid called "gallium(I) iodide." The nature of this species is unclear, but it is useful for the preparation of compounds of gallium(I) and galium(II) and is reported as useful in organic syntheses.
References
C. Brünig, S. Locmelis, E. Milke, M. Binnewies, "Chemischer Transport fester Lösungen. 27. Mischphasenbildung und chemischer Transport im System ZnSe/GaAs" Zeitschrift für anorganische und allgemeine Chemie 2006, 632, 6 , 1067 - 1072. doi:10.1002/zaac.200600008
Baker, Robert J.; Jones, Cameron. ""GaI": A versatile reagent for the synthetic chemist" Dalton Transactions (2005), (8), pp. 1341-1348. doi:10.1039/b501310k
GaI: A new reagent for chemo- and diastereoselective C–C bond forming reactions, Green SP, Jones C., Stasch A., Rose R.P, New J. Chem., 2007, 31, 127 - 134, doi:10.1039/b613669a