Ionothermal Synthesis and Magnetic Studies of Novel Two-Dimensional Metal−Formate Frameworks

Five novel two-dimensional frameworks containing formate-bridged metal-centered octahedra are synthesized ionothermally from two ionic liquids previously unused as solvents in hybrid synthesis, 2-hydroxyethylammonium (HEA) formate, and 1-hydroxy-3-proplyammonium (HPA) formate. Templating effects of the cation from each ionic liquid drive the formation of different structures. [NH3C2H4OH]2[M(CHO2)4] (1: M = Co, 2: M = Ni) exhibit the same stoichiometry and connectivity as their manganese analogue (3: M = Mn), but the manganese form exhibits a different topology from 1 and 2. [NH3C3H6OH][M(CHO2)3(H2O)] (4: M = Co, 5: M = Mn) were synthesized using the HPA formate ionic liquid with a metal−formate connectivity related to those of 1−3. Canted antiferromagnetic ordering occurs at low temperatures (1: TN = 7.0 K, 2: TN = 4.6 K, 3: TN = 8.0 K, 4: TN = 7.0 K, 5: TN = 9.2 K), similar to the magnetic properties previously reported for other metal−formate hybrid materials.

本研究采用两种此前未在杂化合成（hybrid synthesis）中用作溶剂的离子液体（ionic liquids）——甲酸2-羟乙基铵（2-hydroxyethylammonium，HEA）与甲酸1-羟基-3-丙基铵（1-hydroxy-3-propylammonium，HPA）——通过离子热合成法（ionothermal synthesis），制备出五种包含甲酸根桥联金属中心八面体（formate-bridged metal-centered octahedra）的新型二维骨架材料。
两种离子液体的阳离子所产生的模板效应，主导了不同骨架结构的形成。
化学式为[NH₃C₂H₄OH]₂[M(CHO₂)₄]的化合物1（M=Co）与2（M=Ni），其化学计量比（stoichiometry）与连接方式（connectivity）均与锰系类似物3（M=Mn）一致，但锰基化合物3的拓扑结构（topology）与1、2存在差异。
采用HPA甲酸盐离子液体合成的化学式为[NH₃C₃H₆OH][M(CHO₂)₃(H₂O)]的化合物4（M=Co）与5（M=Mn），其金属-甲酸根连接方式与1~3相关类似。
五种化合物均在低温下表现出倾斜反铁磁有序（canted antiferromagnetic ordering），其中1的奈耳温度（TN）为7.0 K，2为4.6 K，3为8.0 K，4为7.0 K，5为9.2 K，其磁学性质与此前报道的其他金属-甲酸根杂化材料相似。