Open-framework iron phosphates: Syntheses, structures, sorption studies and oxidation catalysisThis article is based (partly) on a presentation which will be made at the European Research Conference (EURESCO) on "Molecular Crystal Engineering - EuroConference on Design and Preparation of Molecular Materials" (Acquafredda di Maratea, Italy, 31 May - 5 June 2003) organised by the European Science Foundation and supported by the European Commission, Research DG, Human Potential Programme, High-Level Scientific Conferences, Contract HPCF-CT-2002-00270. This information is the sole responsibility of the author(s) and does not reflect the ESF or Community's opinion. The ESF and the Community are not responsible for any use that might be made of data appearing in this publication.

The iron phosphates [C4H12N2][FeII(H2O)6](HPO4)2 (1), 3∞{[NH4][FeIII2(OH)(PO4)2(H2O)]·H2O} (2) and 3∞{[C4H12N2][FeIII3(PO4)3(HPO4)(H2O)]·∼0.25H2O}, (3) were synthesized by hydrothermal methods and their single-crystal X-ray structures were determined. While compound 1 is only an extended hydrogen bonded network of its three ionic building blocks, compounds 2 and 3 are three-dimensional open-framework materials albeit of different porosity. The structure of 2 corresponds to the mineral sphenicidite. The iron building blocks in 3 are pairs of distorted edge-sharing {FeO6} octahedra and a five-coordinated iron atom, {FeO5}, with a mostly trigonal-bipyramidal polyhedron. The oxidation-state assignment of 2 was backed by 57Fe Mössbauer spectroscopy. Thermogravimetric analysis (TGA) of 2 and 3 shows clearly separated steps of weight loss due to the loss of water of crystallization, aqua ligand and amine template molecules. X-ray powder diffractometry proved that the empty host-frameworks were still intact after heating to 215 °C. The porous empty frameworks of 2 and 3 could be employed as sorbents towards alkanes, alcohols, chlorinated halocarbons, amines and ethers. The larger-porous framework of 3 (but not that of 2) was found to be a catalyst for the highly regioselective oxidation of n-pentane to 3-pentanol with air at 15 bar and 100 °C.