Attempts have been made to synthesise thio-fluoride species of tantalum, osmium and iridium. The reaction of tantalum thiotrichloride and tri- bromide with an excess of anhydrous HF yields [SH3]+ [Ta2F11]-. When anhydrous HF is added to a solution of TaSX3 (X =C1 or Br) in aceto- nitrile an oil is formed which contains =NH and ENH+. The thermal reactions of the hexafluorides of osmium and iridium with zinc and boron sulphides yield the adducts SF4.MF5 (M=Os or Ir). Infra-red and X-ray powder diffraction studies indicate that they have contributions to the bonding from the ionic formulations [SF3]+ [MF6]-. The reaction of MF6 with antimony sulphide in anhydrous HF gives only lower oxidation-state fluorides. The reaction of the alkali metal fluorides with tungsten thiotetra-fluoride in anhydrous HF has yielded the first examples of solids containing [W2S2F9]- and [WSF5]-, viz. M+[W2S2F9]- (M=Li, Na, K, Rb or Cs) and M+[WSF5]- (M=Rb or Cs). Nitrosyl fluoride reacts rapidly with tungsten thiotetrafluoride to yield [NO]+ [WOF5]-, [NO]2+ [WF8]2- and sulphuryl fluoride. However, a low-temperature n.m.r. study has shown that the reaction initially yields [W2S2F9]- and [WSF5]-. Tungsten oxidetetrafluoride reacts with an excess of sulphur tetra-fluoride to give [SF3]+ [W2O2F9]-. X-ray powder diffraction, infra-red and n.m.r. studies have shown that fluorine bridging between [SF3]+ and [W2O2F9]- in the solid state or in solution in sulphur dioxide is minimal. The reaction between tungsten thiotetrafluoride and sulphur tetrafluoride yields only tungsten hexafluoride and sulphur. Xenon difluoride reacts violently with tungsten thiotetrafluoride in the solid state to yield tungsten hexafluoride, xenon and fluorides of sulphur. When the reaction is conducted in sulphuryl chloride fluoride at low-temperature a red-brown solution is formed. This has been shown to consist of tungsten hexafluoride and the radical cation, S8+. by n.m.r. and e.s.r. spectroscopy. The standard enthalpy of formation of tungsten thiotetrafluoride has been determined by hydrolysis in alkaline media.