Formation of metal-anion arrays within layered perovskite hosts. Preparation of a series of new metastable transition-metal oxyhalides, (MCl)LaNb2O7 (M = Cr, Mn, Fe, Co)

A new series of transition-metal oxyhalides (MCl)LaNb 2 O 7 (M = Cr, Mn, Fe, Co) have been prepared by a simple topochemical route. Layered perovskite hosts (ALaNb 2 O 7 , A = Li, Na, K or Rb) were reacted with the corresponding anhydrous metal halides under mild reaction conditions (<400 °C). The compounds were examined by X-ray powder diffraction; the series appears to be isostructural with (CuCl)LaNb 2 O 7 , and the layer spacings, with the exception of M = Co, follow the trend expected from transition-metal cationic radii. Thermal analysis with differential scanning calorimetry (DSC) shows the materials to be metastable where all four compounds decompose exothermically above 690 °C.