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

Abstract

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.

Synthesis of Titanium Fluorophosphates and Fluorosulfates from Hexafluorotitanic Acid

“…[1][2][3][4][5] (x = 0, 0.70, 1.00, 1.25)]. In all but the tavorite-like structure, the fluoride ions are terminal and orient towards inter-framework space or counter cations, as with the 2D structure reported here (structure I).…”

“…[1][2][3][4] Such materials are of interest due to the functionality that arises from rigid and stable structures containing channels or pores, for example by making them highly suited to applications as battery cathode and anode materials. [5] Other applications of transition metal framework and layer structures based on linked polyhedral units include catalysis, molecular separations and, potentially, optoelectronic and magnetic material uses.…”

“…[1][2][3][4][5]14,15] In the work reported herein we have employed hexafluorotitanic acid, H 2 TiF 6 , instead of titanium fluorides as a reactant to maintain high fluoride ion concentrations in the reaction medium.…”

Synthesis, Crystal Structure, and Properties of Mn(PO3F)(H2O)2

“…Some more complex monofluorophosphates including trivalent firstrow transition metals, or ammonium, alkali, or alkaline earth besides divalent first-row transition metals were reported recently. [16,17] Monofluorophosphates can be prepared by various methods. Dependent on the counter cation, solid-state reactions between corresponding metal phosphates and fluorides, flux reactions in fluoride melts, reaction of free fluorophosphoric acid with metal carbonates or hydroxides, metathesis reaction of [43] Coef.…”

Synthesis and characterization of mixed-valence manganese fluorophosphate and analogues with clathrate-like structures: MnIII6F12(PO3(OH))8[Na8(Kx(H3O)4−x(H2O)2)MIV(OH)6] (MIV = Mn, Ti, Ge)

“…10,[17][18][19] Here we have synthesized the title compounds via a similar water-deficient hydrothermal route with phosphoric acid as the sole solvent. 10,[17][18][19] Here we have synthesized the title compounds via a similar water-deficient hydrothermal route with phosphoric acid as the sole solvent.…”