Fluoride-Rich, Hydrofluorothermal Routes to Functional Transition Metal (Mn, Fe, Co, Cu) Fluorophosphates

Hydrofluorothermal methods are shown to offer a facile route to a very large family of mid-late first row, transition metal fluorophosphates with 50 new compounds identified to date for manganese(III), iron(III), cobalt(II), and copper(II). Reactions of a transition metal fluoride with a phosphate source in a very low-water, high-fluoride content system and in the presence of framework charge balancing metal cations or template molecular cations, lead to materials with structures formed from linked M(O,F)n and P(O,F)n polyhedra. The structures of these materials, which contain a variety of 1, 2, and 3-dimensional motifs with a level of framework termination dependent upon their fluoride content, show numerous useful characteristics for functionality and applications. The new and unusual features of these fluorophosphate materials include interlayer spaces or channels lined with fluoride ions, metal polyhedra, M(O,F)n, linked through vertex, edge, or face-sharing, and μ2, μ3, and μ4 bridging fluoride ions. Preliminary characterization of the properties of some of these metal fluorophosphates is reported, including reductive lithium ion insertion, of interest for Li-ion battery positive electrodes, ion exchange reactions, the formation of nanoporous material derivatives through template destruction, and magnetic susceptibility behaviors.

研究表明，氟水热法（Hydrofluorothermal）可为一大类第一过渡系后段过渡金属氟磷酸盐（fluorophosphate）提供简便合成路径，目前已针对锰(III)、铁(III)、钴(II)及铜(II)体系确认得到50种新型化合物。在低水高氟体系中，于骨架电荷平衡金属阳离子或模板分子阳离子存在下，使过渡金属氟化物与磷源发生反应，可得到由相互连接的M(O,F)ₙ与P(O,F)ₙ多面体构成的晶体材料。此类材料的结构包含丰富的1维、2维及3维结构基元，其骨架终端化程度随氟含量变化；该类结构具备诸多可用于功能开发与实际应用的优良特性。这类氟磷酸盐材料的新型非常规结构特征包括：由氟离子修饰的层间空间或通道、通过顶点、边或面共享方式连接的金属多面体M(O,F)ₙ，以及μ₂、μ₃、μ₄桥联氟离子。本文还对部分此类金属氟磷酸盐的性能进行了初步表征，包括可应用于锂离子电池正极材料的还原型锂离子嵌入反应、离子交换反应、通过去除模板制备纳米多孔材料衍生物的过程，以及磁化率行为。