Water-containing derivative phases of the Srn+1FenO3n+1 series

The n=1, 2, 3 and ∞ members of the homologous series Srn+1FenO3n+1 of layered iron oxides are investigated for their tendency to accept additional layers of water in their crystals. The phases possess a Ruddlesden–Popper-type SrO-(SrO-FeO2)n crystal structure, where the n=∞ limit is nothing but the perovskite structure. It is revealed that the n=1, 2 and 3 phases readily accommodate one or two layers of water between adjacent SrO layers, whereas the n=∞ member which lacks the SrO–SrO double-layer unit remains intact in the presence of water. The speed of the water intercalation process is found to decrease with increasing n. Among the layered water derivatives, the n=2 phase with two water molecules per formula unit, i.e. Sr3Fe2O7·2H2O, was found to be most stable.