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.