[Fe-4(PO4)(4)F-2(H2O)(3)]center dot[C6H14N2] or ULM-12, the first magnetic ferric phosphate with an open structure: Hydrothermal synthesis, structure, and magnetic properties

The first three-dimensional magnetic ferric phosphate with an open structure [Fe-4(PO4)(4)F-2(H2O)(3)].[C6H14N2] has been hydrothermally synthesized (453 K, 24 h, autogeneous pressure) from a mixture of Fe2O3, H3PO4, HF, 1,4-diazabicyclo [2.2.2] octane (DABCO), and H2O in the ratio 1:2:2:0.5:80. The structure was determined by single crystal X-ray diffraction. It is monoclinic (space group P2(1)/n (n degrees 14)) with a = 9.987(1) Angstrom, b = 12.275(1) Angstrom, c = 17.462(1) Angstrom, beta = 102.78(1)degrees, V = 2088(1) Angstrom(3), Z = 4. The structure, refined to wR(2)(F-2) = 0.062, R(F) = 0.026 from 5,286 reflections (I> 2 sigma(I), is three-dimensional. The complex framework is built up from two types of secondary building units. In the hexamer [Fe-3(PO4)(3)F-2(H2O)(2)],Fe3+ octahedra form via fluorine atoms corner sharing trimers that are capped by three PO4 tetrahedra. These hexamers share four vertices along [010] and form infinite columns. These columns are linked together along [100] and [001] by dimers [FePO7(H2O)] formed by the O linkage between a Fe3+ square pyramid and a PO4 tetrahedron. The resulting framework leaves large cages limited by 3-, 4-, 6-, and 8-membered windows in which the diprotonated amines are located. Upon heating, water molecules are lost between 150 and 260 degrees C. At 350 degrees C, the decomposition is achieved and leads to FePO4. The title compound orders antiferromagnetically at T-N = 10.7(1) K. Mossbauer spectroscopy confirms the presence of four distinct Fe3+ sites in the structure.