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 Fe-57 Mossbauer 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, P2(1)/n (No. 14), a = 5.8063(1) angstrom, b = 10.3867(3) angstrom, c = 14.8094(4) angstrom, beta = 96.926(1)degrees, and Z = 2. Crystal data for the Mn compound are the same as those for the Fe compound except a = 5.8734(9) angstrom, b = 10.557(2) angstrom, c = 14.863(2) angstrom, and beta = 96.691(2)degrees.