Synthesis and structural characterization of two polymorphs of Fe(2,2′-bpy)(HPO4)(H2PO4)

Two polymorphs of an organic-inorganic hybrid compound, Fe(2,2′-bpy)(HPO₄)(H₂PO₄) (1 and 2) (2,2′-bpy=2,2′-bipyridine), have been synthesized by hydrothermal methods and structurally characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility. Crystal data are as follows: Polymorph 1, monoclinic, space group P2₁/n (No. 14), a=10.904(2) Å, b=6.423(1) Å, c=19.314(3) Å, β=101.161(3)°, and Z=4; Polymorph 2, monoclinic, space group P2₁/c (No. 14), a=11.014(1) Å, b=15.872(2) Å, c=8.444(1) Å, β=109.085(3)°, and Z=4. Polymorph 1 adopts a chain structure in which each iron atom is coordinated by two nitrogen atoms from 2,2′-bpy ligand and four phosphate oxygen atoms. These infinite chains are extended into a 3-D supramolecular array via π-π stacking interactions of the lateral 2,2′-bpy ligands. The structure of polymorph 2 consists of the same building units, namely FeO₄N₂ octahedron, HPO₄ and H₂PO₄ tetrahedra, and 2,2′-bpy ligand, which are linked through their vertices forming an undulated sheetlike structure with 4,12 network. Adjacent layers are extended into a 3-D array via π-π stacking interactions of the aromatic groups. Magnetic susceptibility measurement results confirm that the iron atoms in both compounds are present in the +3 oxidation state.