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

Abstract

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.

Organohalide Precursors for the Continuous Production of Photocatalytic Bismuth Oxyhalide Nanoplates

“…This work establishes organohalides as a general source of halide ions that should be applicable to other oxyhalide materials, even beyond USS syntheses (e.g., hydrothermal routes). This is in complement to work by Rabuffetti and co-workers that demonstrated metal trifluoroacetates as precursor complexes toward layered perovskite systems where the fluorinated ligand provides the necessary F – for the reactions. − In aqueous solution, Bi 3+ and X – react quickly to form BiOX as a precipitate except at extremely low pH values. With this in mind, we hypothesized that Br – and Cl – were being generated from the organohalides at elevated temperatures within the droplets via nucleophilic substitution, with water acting as a nucleophile. − …”

Synthesis, Structure, and Luminescence of Mixed-Ligand Lanthanide Trifluoroacetates

“…Lanthanide trifluoroacetates of formula Ln­(tfa) 3 (H 2 O) 3 (lanthanide Ln = Y; tfa = trifluoroacetate) are routinely employed in the synthesis of downconverting and upconverting phosphors such as LnF 3 and NaLnF 4 . , Ln­(tfa) 3 (H 2 O) 3 belongs to the family of mono- and bimetallic trifluoroacetates whose reactivity as fluorinated precursors to single- and mixed-metal fluorides is well-established. − By contrast, the potential of trifluoroacetates as hybrid organic–inorganic solid-state emitters has been largely overlooked. In the case of Ln­(tfa) 3 (H 2 O) 3 , this gap stems from (1) the low absorptivity of 4 f –4 f transitions, which leads to weak luminescence upon direct excitation of trivalent lanthanides, (2) the very large energy gap between the singlet and triplet states of the trifluoroacetate anion (>13000 cm –1 ), − which prevents it from acting as an efficient sensitizer of lanthanide luminescence via intersystem crossing followed by triplet-to-4 f energy transfer, and (3) water molecules directly coordinated to the lanthanide ion, which tend to quench luminescence via multiphonon relaxation of the excited 4 f levels.…”

Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO2

“…Polycrystalline bi-and monometallic trifluoroacetates were synthesized via solvent evaporation. 5,23 The procedure for the preparation of phasepure K 4 Mn 2 (tfa) 8 and Cs 3 Mn 2 (tfa) 7 (tfaH) is described in detail elsewhere. 5 Monometallic trifluoroacetates KH(tfa) 2 and CsH(tfa) 2 were synthesized by dissolving the corresponding metal carbonate (1 mmol) in a mixture of 3 mL of tfaH and 3 mL of double-distilled water in a 50 mL two-neck roundbottom flask.…”

“…For a number of years our group has been working on the synthesis, crystal-chemistry, and reactivity of bimetallic trifluoroacetates. [1][2][3][4][5] We have established that the trifluoroacetato ligand (tfa = CF 3 COO -) can bridge atoms with dissimilar electronic and geometric requirements and that this ability can be exploited to synthesize bimetallic trifluoroacetates featuring alkali-manganese(II), 1,5 alkaline-earth-manganese(II), 2 and alkali-alkaline-earth pairs. 4 K 2 Mn 2 (tfa) 6 (tfaH) 2 (H 2 O), CsMn(tfa) 3 , K 2 Mn(tfa) 4 , Cs 3 Mn 2 (tfa) 7 (tfaH), Ca 3−x Mn x (tfa) 6 (H 2 O) 4 , and RbCa(tfa) 3 are some examples of this family of solid-state materials.…”

“…1 Likewise, thermolysis of K 2 Mn(tfa) 4 and Cs 3 Mn 2 (tfa) 7 (tfaH) provides synthetic access to layered fluoroperovskites K 2 MnF 4 and Cs 2 MnF 4 , respectively. 5 More recently, we began studying the thermal decomposition of bimetallic trifluoroacetates in fused quartz sealed tubes. Our main goal was to probe the ability of these solids to fluorinate amorphous SiO 2 (a-SiO 2 ), which could eventually open up a new solid-state route to ternary and quaternary fluorosilicates.…”