Two porous iron phosphates were synthesized hydrothermaly from a reaction mixture of FeCl3:H3PO4:1,2-diaminoethane:H2O in the molar ratio 1:3:5:70. The chemical formulas indicate difference only in water content; however, the crystal structures and thermal behaviour of the iron phosphates are completely different. After the removal of 1,2-diaminoethane and water, both products exhibit structural transformation.