Alkali-manganese(II) trifluoroacetates were synthesized, and their potential as single-source precursors for the solid-state and solution-phase synthesis of AMnF fluoroperovskites (A = Na, K, Rb, Cs) was demonstrated. Crystals of NaMn(tfa)(tfaH), KMn(tfa)(tfaH)·HO, RbMn(tfa)·HO, and CsMn(tfa) (tfa = trifluoroacetato) were grown via solvent evaporation and their crystal structures solved using single-crystal X-ray diffraction (XRD). Chemical purity was confirmed using thermal analyses (TGA/DTA) and Rietveld analysis of powder XRD patterns. Thermal decomposition of NaMn(tfa)(tfaH), KMn(tfa)(tfaH)·HO, RbMn(tfa)·HO, and CsMn(tfa) in both the solid state and solution phase yielded crystalline, single-phase NaMnF, KMnF, RbMnF, and CsMnF fluoroperovskites, respectively. Nanocrystals (<100 nm) and submicrocrystals (<500 nm) were obtained in a mixture of high-boiling-point organic solvents. Crystal structures of bimetallic trifluoroacetates displayed a variety of building blocks, coordination environments of the alkali atoms, and coordination modes of the trifluoroacetato ligand. Alkali-fluorine interactions ranging from chemical bonds to short contacts were observed throughout the series. The coordination flexibility of the trifluoroacetato ligand was attributed to the ability of the -CF groups to interact with alkali atoms over a broad range of distances. The synthetic approach described in this investigation provides a starting point to expand the library of fluorinated single-source precursors suitable for solution-phase routes to mixed-metal fluorides.

Three novel bimetallic hybrid crystals featuring rubidium−alkaline-earth metal pairs and trifluoroacetato ligands were synthesized, and their utility as self-fluorinating single-source precursors to the corresponding mixed-metal fluorides was demonstrated. Rb 2 Mg 2 (tfa) 6 (tfaH) 2 •3H 2 O, RbCa(tfa) 3 , and RbSr 2 (tfa) 5 (tfa = CF 3 COO − ; tfaH = CF 3 COOH) were synthesized in both single-crystal and polycrystalline forms via solvent evaporation. Their crystal structures were solved using single-crystal X-ray diffraction (XRD), and chemical purity was confirmed using thermal analysis (TGA/DTA). Metal−oxygen−metal connectivity in Rb 2 Mg 2 (tfa) 6 (tfaH) 2 •3H 2 O was restricted to four-metal building blocks. In contrast, RbCa(tfa) 3 and RbSr 2 (tfa) 5 were found to be extended inorganic hybrids (Cheetham et al. Chem. Commun. 2006, 0, 4780−4795) exhibiting infinite metal connectivity in three and two dimensions, respectively. Systematic analysis of the coordination modes of the trifluoroacetato ligand revealed its ability to bridge alkali and alkaline-earth metals. Rietveld analysis of powder X-ray diffraction data (PXRD) showed that thermal decomposition of Rb 2 Mg 2 (tfa) 6 (tfaH) 2 •3H 2 O and RbCa(tfa) 3 under inert atmosphere yielded crystalline RbMgF 3 and RbCaF 3 , respectively. This solid-state transformation occurred without the need for an external fluorinating agent because the trifluoromethyl group acted as a built-in fluorine source. Solid-state and solution thermolysis of Rb 2 Mg 2 (tfa) 6 (tfaH) 2 •3H 2 O provided access to the hexagonal and cubic polymorphs of the fluoroperovskite RbMgF 3 , respectively. Findings reported in this article highlight that bimetallic trifluoroacetates offer unique features from the standpoint of both crystal lattice topology and reactivity.

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.

Owing to their potential as single-source precursors for compositionally complex materials, there is growing interest in the rational design of multimetallic compounds containing fluorinated ligands. In this work, we show that chemical and structural principles for a materials-by-design approach to bimetallic trifluoroacetates can be established through a systematic investigation of the crystal-chemistry of their monometallic counterparts. A(CFCOO)·nHO (A = Mg, Ca, Sr, Ba, Mn) monometallic trifluoroacetates were employed to demonstrate the feasibility of this approach. The crystal-chemistry of monometallic trifluoroacetates was mapped using variable-temperature single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis. The evolution with temperature of the previously unknown crystal structure of Mg(CFCOO)·4HO was found to be identical to that of Mn(CFCOO)·4HO. More important, the flexibility of Mn(CFCOO)·4HO (x = 1, 3) to adopt two structures, one isostructural to Mg(CFCOO)·4HO, the other isostructural to Ca(CFCOO)·4HO, enabled the synthesis of Mg-Mn and Ca-Mn bimetallic trifluoroacetates. MgMn(CFCOO)·4HO was found to be isostructural to Mg(CFCOO)·4HO and exhibited isolated metal-oxygen octahedra with Mg and Mn nearly equally distributed over the metal sites (Mg/Mn: 45/55). CaMn(CFCOO)·4HO was isostructural to Ca(CFCOO)·4HO and displayed trimers of metal-oxygen corner-sharing octahedra; Ca and Mn were unequally distributed over the central (Ca/Mn: 96/4) and terminal (Ca/Mn: 38/62) octahedral sites.