Synthesis and characterization of a new open-framework mixed-valence aluminum–iron phosphate (C4H12N2)2[Fe2Al5(PO4)8(H2O)]

A new open-framework aluminum-iron phosphate (C4H12N2)(2)[Fe2Al5(PO4)(8)(H2O)] (denoted as FeAPO-CJ51), with mixed-valence iron (II, III) has been hydrothermally synthesized by using piperazine as the template. The three-dimensional framework of FeAPO-CJ51 is constructed by the connection of metal-centered MOn (M = Fe/Al, n = 4, 5, 6) polyhedra and PO4 tetrahedra, which contains interconnecting 8-ring channels along the [010] and [001] directions. Diprotonated piperazine cations locate in the 8-ring channels to compensate the negative charge of the anionic framework. Mossbauer and magnetic susceptibility measurements show that equal amounts of Fe2+ and Fe3+ are present in FeAPO-CJ51, which undergo the long-range antiferromagnetic interactions.