Bis(pentafluorophenyl) thallium(III) bromide has been prepared from pentafluorophenylmagnesium bromide and thallic chloride, and converted into the corresponding fluoride, chloride, nitrate, acetate, trifluoroacetate, and sulphate. The compounds have low conductances in acetone, and the majority are monomeric. The chloride, bromide, and acetate have low conductances in methanol, but the fluoride, trifluoroacetate, and nitrate are highly ionised. The sulphate is a strong electrolyte in water. In benzene, the chloride and bromide are dimeric. In the solid, the bromide, chloride, and fluoride are probably dimeric, the nitrate contains ionic or weakly co-ordinated nitrate groups, while the sulphate has bridging bidentate sulphate groups. With 2,2′-bipyridyl (bipy) and 1,10-phenanthroline (o-phen) , complexes of the type (C 6F 5) 2 (bipy or o-phen)TlX (X is Cl, Br, NO 3, and CF 3·CO 2) are formed. Infrared data indicate these probably contain five co-ordinate thallium. The bipyridyl complexes arc very weak electrolytes in acetone and molecular weights are consistent with slight ionisation. The phenanthroline complexes are nonelectrolytes and monomeric. In methanol, all complexes are moderately or highly ionised. Representative complexes are monomeric or slightly associated in benzene. An unstable complex, (C 6F 5) 2py 2TlBr, has also been prepared. Complexes of the type Q[(R f) 2TlX 2] (Q is Ph 4P, Et 4N; X is Cl, Br) have been prepared and are 1:1 electrolytes in acetone and methanol. The infrared spectra of the chloro-complexes are consistent with the presence of the tetrahedral (C 6F 5) 2TlCl 2 - ion. (C 6F 2) 2TlBr reacts with sodium tetraphenylborate, triphenylbismuth, and diphenylmercury with the formation of diphenylthallium bromide.