ULM-12 and ULM-19: The hydrated and anhydrous forms of the first synthetic oxyfluorinated iron phosphate with an open structure

ULM-19 or [Fe-4(PO4)(4)F-2], [C6H14N2], was obtained in a monocrystalline form from the dehydration of single crystals of ULM-12, or [Fe-4(PO4)(4)F-2(H2O)(3)], [C6H14N2] at 260 degrees C. It is monoclinic (S.G. P2(1)/n) with a = 10.009(7), b = 12.235(8), c = 17.28(2) Angstrom, beta = 106.04(5)degrees, V = 2034(3) Angstrom(3), Z = 4. Its structure, which can be described from the corner sharing of hexameric Fe3P3 and dimeric FeP units, directly derives from that of ULM-12 by the loss, on three of the four Fe(III) polyhedral sites of the structure of ULM-12, of the terminal water molecules. This induces drastic changes in the coordination polyhedra of Fe(III): three octahedra and one square pyramid in ULM-12, and one octahedron, one square pyramid, one trigonal bipyramid and one tetrahedron in ULM-19. These evolutions were confirmed and characterized by in situ Mossbauer spectrometry measurements using a cryofurnace. The loss of water opens 6-ring channels beside the 12-ring tunnels already existing in ULM-12.