Rubidium–Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors to Mixed-Metal Fluorides

Abstract

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.

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. − …”

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

“…All four bimetallic trifluoroacetates belong to the family of extended inorganic hybrids in which infinite metal–(O or F)–metal connectivity is observed in at least one dimension. The counterintuitive ability of the trifluoroacetato ligand to afford access to this class of extended solids has been previously highlighted by our group. − Na 2 Mn­(tfa) 4 crystallizes in the triclinic P space group and exhibits infinite metal–O–metal connectivity in one dimension (Figure a). The building block of this hybrid consists of zigzag chains of edge-sharing Na­(O or F) 6,7 dimers alternated with MnO 6 octahedra (Figure b).…”

“…An analogous figure is provided in the Supporting Information for rubidium atoms in Rb 4 Mn 2 (tfa) 8 ·0.23H 2 O (Figure S5). In this work, we define the first coordination shell of alkali metals using the same cut-off distances for metal−organofluorine contacts as those we used in previous studies; these are 3.0 (Na), 3.3 (K), 3.6 (Rb), and 3.7 Å (Cs). ,, These values are comparable to those used by Plenio in his review of the coordination chemistry of CF units in metal–organic compounds, where he set 3.07 (Na), 3.47 (K), 3.67 (Rb), and 3.87 (Cs) Å as thresholds . A comprehensive list of metal–O and metal–F distances used to define the first coordination shell of alkali and manganese atoms is given in the Supporting Information (Table S14).…”

“…In this contribution we expand the synthetic accessibility of layered fluoroperovskites A 2 MnF 4 using metal–organic precursors consisting of alkali–manganese pairs bridged by trifluoroacetato ligands. Previous studies by our group have shown that solid-state and solution thermolysis of bimetallic trifluoroacetates provide facile access to a number of mixed-metal fluorides, including NaMnF 3 , KMnF 3 , RbMnF 3 , CsMnF 3 , RbMgF 3 , and RbCaF 3 . , One of the most appealing features of this approach is that it eliminates the need for external fluorinating agents, as trifluoromethyl groups belonging to trifluoroacetato ligands (CF 3 COO – , tfa) act as a de facto fluorine source. Additionally, crystallization of the target mixed-metal fluorides occurs at relatively low temperatures (≈200–300 °C).…”

Chemistry of alkaline earth metals: It is not all ionic and definitely not boring!

“…Molecular as well as polymer trifluoroacetate compounds were obtained mixing alkali and alkaline earth metal ion carbonates in the presence of trifluoroacetic acid. The resulting heterometallic compounds were shown to yield the mixed metal fluorides upon heating [79].…”