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

Abstract

AbstractTopochemical reduction of the n = 2 Ruddlesden‐Popper oxide, LaSr2CoRuO7, yields LaSr2CoRuO5.3, a phase containing (Co/Ru)O4 squares which share corners to form 1D infinite double‐chains. In contrast, fluorination of LaSr2CoRuO7 yields the oxyfluoride LaSr2CoRuO5.5F3.5, which can then be reduced to form LaSr2CoRuO4.5F1.5. This reduced oxyfluoride is almost isoelectronic with LaSr2CoRuO5.3, but LaSr2CoRuO4.5F1.5 has a crystal structure in which the (Co/Ru)O4 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 LaSr2CoRuO5.3 and LaSr2CoRuO4.5F1.5 adopt glassy magnetic states at low temperature, but the magnetic interactions present in LaSr2CoRuO5.3 appear to be significantly stronger than those in LaSr2CoRuO4.5F1.5, attributable to the differing dimensionality of the transition‐metal connectivity. The structural features of LaSr2CoRuO5.5F3.5 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.