Synthesis and crystal structures of iron hydrogen phosphates

Abstract

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 Fe_1.34(III)(PO₄)OH_0.96 (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 HPO₄groups. 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 NH₄⁺, for battery applications is discussed.