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 RbLaNb2O7 and CuX2 (X = Cl, Br) results in a new set of layered copper-oxyhalide perovskites, (CuX)LaNb 2O7. Rietveld structural analysis of X-ray powder diffraction data confirms the formation of a two-dimensional copper-halide network in the double-lay ered perovskite interlayer. This new structure type contains unusual CuO2X4 octahedra that corner-share with NbO6 octahedra from the perovskite slab a nd edge-share with each other along all four equatorial edges. Magnetic sus ceptibility measurements show that both products exhibit antiferromagnetic transitions below 40 K. Additionally, these materials are found to be low-t emperature phases, decomposing completely by 700 degrees C. The synthetic a pproach described in this work is significant in that it demonstrates how h ost structures can be used as templates in the directed low-temperature ass embly of extended metal--anion arrays.