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 = 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)°.本研究以氯化胆碱与丙二酸的低熔共晶混合物作为溶剂，成功合成了两种通式为Na₂M₃(C₂O₄)₃(CH₃PO₃H)₂（其中M为Fe²⁺和Mn²⁺）的同构过渡金属草膦酸盐（transition-metal oxalatophosphonates），并通过单晶X射线衍射（single-crystal X-ray diffraction）与⁵⁷Fe穆斯堡尔光谱（Mössbauer spectroscopy）对其进行了结构表征。该类化合物的三维骨架结构由共角八面体三聚体构成，该三聚体通过两种具有独特连接模式的草酸盐配体、膦酸根四面体与氢键与其他三聚体相连，沿[101]方向形成可供Na⁺阳离子占据的无限孔道。这也是离子液体（ionic liquid）作为溶剂应用于金属草膦酸盐合成领域的首例报道。铁基化合物的晶体参数如下：单斜晶系，空间群P2₁/n（编号14），晶胞参数a=5.8063(1) Å，b=10.3867(3) Å，c=14.8094(4) Å，β=96.926(1)°，晶胞内化学式单元数Z=2。锰基化合物的晶体参数与铁基化合物基本一致，仅晶胞参数a=5.8734(9) Å，b=10.557(2) Å，c=14.863(2) Å，β=96.691(2)°。