Synthesis and crystal structures of iron hydrogen phosphates.

Three new iron hydrogen phosphate compositions have been synthesised under hydrothermal conditions; Fe(II)2O(HPO4) ( 1), (NH4)3Fe(III)3(HPO4)6 ( 2) and Fe1.34(III)(PO4)OH0.96 ( 3). 1 and 2 have framework structures constructed from FeO6 octahedra and HPO4/PO4 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 HPO4 groups. Crystals of 3 grow as 30 m 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 NH4+, for battery applications is discussed.