Hydrothermal Synthesis, Powder Structural Determination, and Magnetic Study of the Novel Hydrated Iron Diphosphonate [Fe2(H2O)2 (O3P–CH2–PO3H)2](H2O)2 or MIL-13

[Fe2(H2O)2(O3P–CH2–PO3H)2](H2O)2 or MIL-13 was prepared hydrothermally (120 h at 473 K). Its structure was determined by powder X-ray diffraction. This compound crystallizes in the triclinic system (P-1) with the following cell parameters: a=9.8487(6) ?, b=8.0308(5) ?, c=9.9154(5) ?, alpha=99.09(1)°, beta=97.91(1)°, gamma=89.38(1)°, V= 766.97 ?3, Z=2. Its bidimensional structure consists of [Fe2(H2O)2 (O3P–CH2–PO3H)2] sheets, between which are located water molecules. The thermal study indicates that this compound undergoes several phase transitions. Moreover, this new iron diphosphonate shows a 2D antiferromagnetic behavior below 13(1) K, but remains paramagnetic at 4.2 K as shown by M?ssbauer spectroscopy.