Two isostructural transition-metal oxalatophosphonates, Na2M3(C2O4)3(CH3PO3H)2 (M = FeII and MnII), 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)°.