Controlling the Regioselectivity of Topochemical Reduction Reactions Through Sequential Anion Insertion and Extraction

Abstract Topochemical reduction of the n = 2 Ruddlesden‐Popper oxide, LaSr 2 CoRuO 7 , yields LaSr 2 CoRuO 5.3 , a phase containing (Co/Ru)O 4 squares which share corners to form 1D infinite double‐chains. In contrast, fluorination of LaSr 2 CoRuO 7 yields the oxyfluoride LaSr 2 CoRuO 5.5 F 3.5 , which can then be reduced to form LaSr 2 CoRuO 4.5 F 1.5 . This reduced oxyfluoride is almost isoelectronic with LaSr 2 CoRuO 5.3 , but LaSr 2 CoRuO 4.5 F 1.5 has a crystal structure in which the (Co/Ru)O 4 squares are connected into 2D infinite sheets. Thus, by following a fluorinate‐then‐reduce reaction scheme, the regiochemistry of topochemical reduction reactions can be modified, and compounds with different transition‐metal‐centre interconnectivity can be prepared. Both LaSr 2 CoRuO 5.3 and LaSr 2 CoRuO 4.5 F 1.5 adopt glassy magnetic states at low temperature, but the magnetic interactions present in LaSr 2 CoRuO 5.3 appear to be significantly stronger than those in LaSr 2 CoRuO 4.5 F 1.5 , attributable to the differing dimensionality of the transition‐metal connectivity. The structural features of LaSr 2 CoRuO 5.5 F 3.5 that modify the regioselectivity of the topochemical reduction reaction appear to be common to many fluorinated Ruddlesden‐Popper oxides, suggesting this fluorinate‐then‐reduce strategy could be used to prepare a range of “infinite‐layer” reduced phases which cannot be made by direct reduction of Ruddlesden‐Popper oxide precursors.