The arenesulphinatodiorganothallium(III) complexes R2Tl(O2SR’) (R = Et, Me, Ph, or C6F5; throughout R’ = Ph or p-MeC6H4) have been prepared by reaction of the appropriate diorganothallium(III) halides and silver arenesulphinates, and gave the complexes Et2(phen)Tl(O2SR’), impure Me2(phen)Tl(O2SR’), Ph2(phen or bpy)Tl(O2SR’), (C6F5)2(phen, bpy, py, or Ph3PO)Tl(O2SR’), and (C6F5)2Ph3AsOTl(O2SPh) on reaction with the appropriate ligands. Attempts to prepare R2(bpy)Tl(O2SPh) (R = Et or Me), (C6F5)2Ph3AsOTl(O2S-p-MeC6H4), (C6F5)2Ph3PTl(O2SPh), and Ph2(Ph3AsO)Tl(O2SPh) failed. The complexes Et2Tl(O2SR’) are dimeric with bridging O-sulphinate groups in chloroform, and weak association of the dimeric units is considered to occur in the solid state. Conclusions are more tentative for R2Tl(O2SR’) (R = Me, Ph, or C6F5) derivatives, since insolubility prevented molecular weight and infrared measurements in solvents of low polarity. However, associated structures with bridging bidentate O-sulphinate groups are likely, and sulphur-oxygen stretching frequencies suggest Me2Tl(O2SR’) and Ph2Tl(O2SR’) have structures similar to Et2Tl(O2SR’). The complexes R2LTl(O2SR’) have monomeric structures with O-sulphinate ligands. For L = phen or bpy, the sulphinate groups are either unidentate, giving five-coordinate thallium, or bidentate, giving six-coordinate thallium, and for L = py, Ph3PO, or Ph3AsO, unidentate sulphinate groups and four-coordinate thallium are likely.