Assembly of Metal−Anion Arrays within a Perovskite Host. Low-Temperature Synthesis of New Layered Copper−Oxyhalides, (CuX)LaNb₂O₇, X = Cl, Br

A low-temperature topotactic route is used to assemble metal−anion arrays within a perovskite host. Ion exchange between RbLaNb 2 O 7 and CuX 2 (X = Cl, Br) results in a new set of layered copper−oxyhalide perovskites, (CuX)LaNb 2 O 7 . Rietveld structural analysis of X-ray powder diffraction data confirms the formation of a two-dimensional copper−halide network in the double-layered perovskite interlayer. This new structure type contains unusual CuO 2 X 4 octahedra that corner-share with NbO 6 octahedra from the perovskite slab and edge-share with each other along all four equatorial edges. Magnetic susceptibility measurements show that both products exhibit antiferromagnetic transitions below 40 K. Additionally, these materials are found to be low-temperature phases, decomposing completely by 700 °C. The synthetic approach described in this work is significant in that it demonstrates how host structures can be used as templates in the directed low-temperature assembly of extended metal−anion arrays.