OXYFLUORINATED OPEN FRAMEWORK COMPOUNDS - XVIII - DEHYDRATION OF SINGLE-CRYSTALS OF THE IRON PHOSPHATE ULM-12 OR [FE-4(PO4)(4)F-3(H2O)(3),N2C6H14] WITH AN OPEN STRUCTURE, STRUCTURAL DETERMINATION AND MAGNETIC STUDY OF THE DEHYDRATED PHASE (ULM-19)

[Fe-4(PO4)(4)F-3(H2O)(3),N2C6H14] or ULM-12 was the first magnetic iro n phosphate with an open framework. The dehydration of single crystals of ULM-12 led to a new compound, [Fe-4(PO4)(4)F-3,N2C6H14] named ULM- 19. Its structure was determined by single-crystal X-ray diffraction. ULM-19 is monoclinic [space group P2(1)/n (no. 14)] with lattice param eters a = 10.009(7) Angstrom, b = 12.235(8) Angstrom, c = 17.28(2) Ang strom, beta = 106.04 degrees, V = 2034(3) Angstrom(3), Z=4. Compared t o ULM-12, the structure of ULM-19 lets appear new six-ring tunnels ind uced by the loss of the water molecules located in the inorganic frame work; a drastic change in the coordination polyhedra of Fe(III) was ob served. These evolutions were confirmed and characterized by in situ M ossbauer spectrometry measurements in a cryofurnace. ULM-19 adopts an antiferromagnetic behaviour under T-N=9(1) K. (C) 1998 Elsevier Scienc e B.V.