Oxyfluorinated open framework compounds -: XIX.: Hydrothermal synthesis, structure determination, and magnetic properties of the iron (III) phosphate [Fe3(PO4)3F2, (CH3NH3)2, H2O]:: Comparison with the isostructural oxyfluorinated gallophosphate ULM-4

[Fe-3(PO4)(3)F-2, (CH3NH3)(2), H2O] or ULM-4 is a new iron phosphate with an open framework synthesized by a hydrothermal method (72 h at 453 K). The structure was solved by X-ray diffraction on single crystal. ULM-4 crystallizes in the monoclinic system (space group P2(1)/n (no. 14)) with cell parameters at 293 K: a = 8.8494(1), b = 10.3728(1), c = 16.9471(1) Angstrom, beta = 92.869 degrees(1), V = 1553.68 (2) Angstrom(3), Z = 4. Its structure was refined to R-1(F-0) = 0.0276, wR(2)(F-0(2) = 0.0741 (5033 independent reflections with I> 2 sigma(I)). This compound is isostructural with the oxyfluorides gallophosphate ULM-4. Its three-dimensional framework is built up from corner-sharing hexameric units, thus delimiting 10-membered channels along [010] in which methylamine and water molecules are inserted. It also exhibits 8-membered channels along [100]. A phase transition occurs at 265 K. This new compound exhibits an antiferromagnetic behavior below 25(1)K. Mossbauer spectrometry confirms the crystallographic results. (C) 1997 Academic Press.