Hybrid Open-Framework Iron Phosphate-Oxalates Demonstrating a Dual Role of the Oxalate Unit

Abstract

New inorganic-organic hybrid open-framework materials of the phosphate-oxalate family, $[Fe_2(H_2O)_2(HPO_4)_2(C_2O_4)]H_2O\cdot(I)$, $[Fe_2(H_2O)_2(HPO_4)_2(C_2O_4)]_2 H_2O\cdot(II)$, $[C_3N_2H_1_2][Fe_2(HPO_4)_2(C_2O_4)_{1.5}]_2 (III)$, and $[C_3N_2OH_1_2][Fe_2(HPO_4)_2(C_2O_4)_{1.5}]_2 (IV)$ have been synthesized hydrothermally in the presence of structure-directing amines. The amine molecules are incorporated in III and IV, whereas I and II are devoid of them. The oxalate units act as a bridge between the layers in all the compounds. The layers in I and II are entirely inorganic, being formed by $FeO_6$ and $PO_4$ units, whereas in III and IV oxalate units constitute the inorganic layers and act as the bridge between these layers. Such a dual role of the oxalate unit is unique and noteworthy. The formation of two types of inorganic layers in I and II consisting of four-, six-, and eight-membered rings, indicates the interconversions between the various rings in the phosphate-oxalates to be facile. All the phosphate - oxalates show antiferromagnetic ordering at low temperatures.