Ionothermal Synthesis of Metal Oxalatophosphonates with a Three-Dimensional Framework Structure:  Na₂M₃(C₂O₄)₃(CH₃PO₃H)₂ (M = Fe^II and Mn^II)

Two isostructural transition-metal oxalatophosphonates, Na₂M₃(C₂O₄)₃(CH₃PO₃H)₂ (M = Fe^II and Mn^II), 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 ⁵⁷Fe Mössbauer spectroscopy. The 3D framework structure consists of a corner-sharing octahedral trimer that is linked with other trimers through two distinct oxalate ligands with unusual linkage types, phosphonate tetrahedra, and H bonds to form infinite channels along the [101] direction where the Na⁺ cations are located. They are the first examples for the use of an ionic liquid as a solvent in the synthesis of metal oxalatophosphonates. Crystal data for the Fe compound follow:  monoclinic, P2₁/n (No. 14), a = 5.8063(1) Å, b = 10.3867(3) Å, c = 14.8094(4) Å, β = 96.926(1)°, and Z = 2. Crystal data for the Mn compound are the same as those for the Fe compound except a = 5.8734(9) Å, b = 10.557(2) Å, c = 14.863(2) Å, and β = 96.691(2)°.