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 μ(2), μ(3), and μ(4) 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.