Bimetallic Trifluoroacetates as Precursors to Layered Perovskites A₂MnF₄ (A = K, Rb, and Cs)

Four novel alkali-manganese(II) trifluoroacetates were synthesized, and their potential as self-fluorinating precursors to layered perovskites A₂MnF₄ (A = K, Rb, and Cs) was demonstrated. Na₂Mn(tfa)₄, K₄Mn₂(tfa)₈, Rb₄Mn₂(tfa)₈·0.23H₂O, and Cs₃Mn₂(tfa)₇(tfaH) (tfa = CF₃COO^- and tfaH = CF₃COOH) were grown as single crystals, and their crystal structures solved using X-ray diffraction. Chemically pure K₄Mn₂(tfa)₈, Rb₄Mn₂(tfa)₈·0.23H₂O, and Cs₃Mn₂(tfa)₇(tfaH) were also prepared in polycrystalline form as confirmed by thermal analysis and powder X-ray diffraction. Thermolysis of these powders yielded the isostructural series K₂MnF₄, Rb₂MnF₄, and Cs₂MnF₄ at low temperatures (≈200-300 °C). Trifluoromethyl groups belonging to the trifluoroacetato ligands served as the fluorine source, thereby eliminating the need for external fluorinating agents. K₂MnF₄ and Rb₂MnF₄ were obtained as single-phase powders, whereas Cs₂MnF₄ crystallized along with CsMnF₃. Access to polycrystalline Cs₂MnF₄ coupled to Rietveld analysis enabled elucidation of the crystal structure of this ternary fluoride, which had remained elusive. Findings presented in this article expand the synthetic accessibility of polycrystalline A₂MnF₄ fluorides, for which a scarce number of routes is available in the literature.