Oxyfluorinated open framework compounds.: XVIII -: Dehydration of single crystals of the iron phosphate ULM-12 or [Fe4(PO4)4F3(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 iron 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 parameters a = 10.009(7) Angstrom, b = 12.235(8) Angstrom, c = 17.28(2) Angstrom, beta = 106.04 degrees, V = 2034(3) Angstrom(3), Z=4. Compared to ULM-12, the structure of ULM-19 lets appear new six-ring tunnels induced by the loss of the water molecules located in the inorganic framework; a drastic change in the coordination polyhedra of Fe(III) was observed. These evolutions were confirmed and characterized by in situ Mossbauer spectrometry measurements in a cryofurnace. ULM-19 adopts an antiferromagnetic behaviour under T-N=9(1) K. (C) 1998 Elsevier Science B.V.