Ionic Liquid of Choline Chloride/Malonic Acid as a Solvent in the Synthesis of Open-Framework Iron Oxalatophosphates

Two new iron(III) oxalatophosphates, Cs₂Fe(C₂O₄)_0.5(HPO₄)₂ (1) and CsFe(C₂O₄)_0.5(H₂PO₄)(HPO₄) (2), have been synthesized by using a low melting point eutectic mixture of choline chloride and malonic acid as a solvent and characterized by single-crystal X-ray diffraction and magnetic susceptibility. Crystal data are as follows:  compound 1, monoclinic, P2₁/c (No. 14), a = 8.5085(4) Å, b = 12.7251(6) Å, c = 9.8961(4) Å, β = 107.117(1)°, V = 1024.01(8) ų, Z = 4, and R₁ = 0.0264; compound 2, monoclinic, P2₁/n (No. 14), a = 8.0038(3) Å, b = 10.2923(3) Å, c = 11.4755(4) Å, β = 100.507(1)°, V = 929.47(5) ų, Z = 4, and R₁ = 0.0311. The structure of 1 comprises FeO₆ octahedra connected by HPO₄^2- tetrahedra and bisbidentate oxalate anions to form a 3D framework containing intersecting 12-ring channels, with the charge-compensating Cs⁺ cations being located at the intersections of these channels. The structure of 2 consists of 2D layers of octahedral FeO₆, tetrahedral H₂PO₄^- and HPO₄^2- moieties, and bisbidentate oxalate ligands with the Cs⁺ cations between the layers. They are the first examples for the use of ionic liquid as a solvent in the synthesis of metal oxalatophosphates.