K2NiF4-type materials have attracted significant interest for a wide range of applications. While perovskite-based Fe oxide fluorides tend not to be thermally stable, e.g. SrFeO2F, related K2NiF4 oxide fluorides have been reported to show good thermal stability, Sr2FeO3F. However the related Co based system, Sr2CoO3F, can only be synthesised by a high pressure route, which limits potential applications. Recently we have shown that the latter phase can be stabilised at ambient pressure by suitable doping strategies. This proposal is targeted at elucidating the crystal and magnetic structures of these new phases, along with the related Fe based systems.