Crystal Growth, Structure, and Magnetic Properties of a New Polymorph of Fe₂P₂O₇

The title compound, a new polymorphic phase of iron diphosphate, was prepared by solid-state reaction. This compound crystallizes in the monoclinic space group P21/c with a = 4.4668(6) Å, b = 9.896(1) Å, c = 5.2077(7) Å, β = 97.516(2)°, V = 228.22(5) Å3, and Z = 2. The structure is characterized by the arrangement of FeO6 octahedra and P2O7 groups. The FeO6 octahedra are connected by edge sharing to form six-membered rings, which are further interconnected to form two-dimensional zigzag sheets perpendicular to the [100] direction. The P2O7 groups link these sheets to build three-dimensional networks. The relation between Fe2P2O7 polymorphs is discussed. Magnetic measurements reveal the presence of antiferromagnetic interactions in the Fe2+ sublattice at about 12.5 K. Magnetization isotherms obtained below the Neel temperature follow a linear variation in the whole range of the magnetic field strength characteristic of the mentioned antiferromagnetic order and metamagnetic (field induced) transitions have not been observed up to 5 T.