Synthesis and crystal structures of iron hydrogen phosphates

Three new iron hydrogen phosphate compositions have been synthesised under hydrothermal conditions; Fe(ii)O(HPO) (1), (NH )Fe(iii)(HPO) (2) and Fe(iii)(PO)OH (3). 1 and 2 have framework structures constructed from FeO octahedra and HPO /PO tetrahedra containing cavities; in the case of 2, these are occupied by ammonium cations while in 1 they are cross linked by hydrogen bonding involving the HPO groups. Crystals of 3 grow as 30 μm octahedral "jackstones" and this synthetic material adopts the structure from the Lipscombite solid solution. Thermal decomposition of these materials yields simple iron phosphates and the potential of these compounds and their derivatives, formed for example through Li-ion exchange of NH, for battery applications is discussed.