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

Two new iron(III) oxalatophosphates, Cs<sub>2</sub>Fe(C<sub>2</sub>O<sub>4</sub>)<sub>0.5</sub>(HPO<sub>4</sub>)<sub>2</sub> (<b>1</b>) and CsFe(C<sub>2</sub>O<sub>4</sub>)<sub>0.5</sub>(H<sub>2</sub>PO<sub>4</sub>)(HPO<sub>4</sub>) (<b>2</b>), 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 <b>1</b>, monoclinic, <i>P</i>2<sub>1</sub>/<i>c </i>(No. 14), <i>a</i> = 8.5085(4) Å, <i>b</i> = 12.7251(6) Å, <i>c</i> = 9.8961(4) Å, β = 107.117(1)°, <i>V</i> = 1024.01(8) Å<sup>3</sup>, <i>Z </i>= 4, and <i>R</i><sub>1</sub> = 0.0264; compound <b>2</b>, monoclinic, <i>P</i>2<sub>1</sub>/<i>n </i>(No. 14), <i>a</i> = 8.0038(3) Å, <i>b</i> = 10.2923(3) Å, <i>c</i> = 11.4755(4) Å, β = 100.507(1)°, <i>V</i> = 929.47(5) Å<sup>3</sup>, <i>Z </i>= 4, and <i>R</i><sub>1</sub> = 0.0311. The structure of <b>1</b> comprises FeO<sub>6</sub> octahedra connected by HPO<sub>4</sub><sup>2-</sup> tetrahedra and bisbidentate oxalate anions to form a 3D framework containing intersecting 12-ring channels, with the charge-compensating Cs<sup>+</sup> cations being located at the intersections of these channels. The structure of <b>2</b> consists of 2D layers of octahedral FeO<sub>6</sub>, tetrahedral H<sub>2</sub>PO<sub>4</sub><sup>-</sup> and HPO<sub>4</sub><sup>2-</sup> moieties, and bisbidentate oxalate ligands with the Cs<sup>+</sup> cations between the layers. They are the first examples for the use of ionic liquid as a solvent in the synthesis of metal oxalatophosphates.