Open-framework iron phosphates: Syntheses, structures, sorption studies and oxidation catalysis

The iron phosphates [C4H12N2](Fe-II(H2O)(6)](HPO4)(2) (1), (3){[NH4]Fe-2(III) (OH)(PO4)(2) (H2O)].H2O} (2) and (3){[C4H12N2][Fe-3(III)(PO4)(3)(HPO4)(H2O)].similar to0.25H(2)O}, (3) were synthesized by hydrothermal methods,and their singe-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 sire 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-shaping {FeO6} octahedra and a five-coordinated iron atom, {FeO5}, with a mostly trigonal-bipyramidal polyhedron. The oxidation-state assignment of 2 was backed by Fe-57 Mossbauer spectroscopy. Thermogravimetric analysis (TGA) of 2 and 3 shows clearly separated steps of weight loss date 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 'degreesC. The porous empty frameworks of 2 and 3 could be employed as sorbents towards alkanes, alcohols, chlorinated halocarbons, amines and ethers. Tie larger-porous framework of 3 (but not that of 2) wets found to be a catalyst for the highly regioselective oxidation of n-pentane to 3-pentanol with air at 15 bar and 100 degreesC.