[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 str ucture [Fe-4(PO4)(4)F-2(H2O)(3)].[C6H14N2] has been hydrothermally syn thesized (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 rat io 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)) wit h a = 9.987(1) Angstrom, b = 12.275(1) Angstrom, c = 17.462(1) Angstro m, beta = 102.78(1)degrees, V = 2088(1) Angstrom(3), Z = 4. The struct ure, refined to wR(2)(F-2) = 0.062, R(F) = 0.026 from 5,286 reflection s (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(P O4)(3)F-2(H2O)(2)],Fe3+ octahedra form via fluorine atoms corner shari ng trimers that are capped by three PO4 tetrahedra. These hexamers sha re four vertices along [010] and form infinite columns. These columns are linked together along [100] and [001] by dimers [FePO7(H2O)] forme d by the O linkage between a Fe3+ square pyramid and a PO4 tetrahedron . The resulting framework leaves large cages limited by 3-, 4-, 6-, an d 8-membered windows in which the diprotonated amines are located. Upo n heating, water molecules are lost between 150 and 260 degrees C. At 350 degrees C, the decomposition is achieved and leads to FePO4. The t itle compound orders antiferromagnetically at T-N = 10.7(1) K. Mossbau er spectroscopy confirms the presence of four distinct Fe3+ sites in t he structure.