Bis(pentafluorophenyl)thallium(III) compounds, (C6F5)2TIX (X = Br, Cl, 1 2SO4, OAc, etc.), are decomposed by iodide ions in boiling aqueous ethanol, aqueous methanol, or water with the formation of thallous iodide and pentafluorobenzene. Analogous reactions are possible with bromide or cyanide ions. However, reaction with acidified iodide or bromide ions gives the corresponding tetrahalothallate(III) complex. The formation of thallous iodide in reactions without added acid is attributed to intermediate formation of the tetraiodothallate(III) complex and base, which then interact to give thallous iodide. The ready decomposition of MTII4 (M = Bu4N or MePh3As) complexes by base to give thallous iodide has been demonstrated. Under suitable conditions, cleavage of bromobis(pentafluorophenyl)thallium(III) with iodide ions gives the triiodopentafluorophenylthallate(III) complex, which has been isolated as the tetrabutylammonium or the methyltriphenylarsonium salt. The new compounds (C6F5)2 TIX (X = I or CN) have been prepared by metathesis between sulphatodi[bis(pentafluorophenyl)thallium(III) and iodide or cyanide ions in water. They are considered to be dimeric with bridging iodide or cyanide groups.