Rubidium–Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors 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. Rb2Mg2(tfa)6­(tfaH)2­·3H2O, RbCa­(tfa)3, and RbSr2(tfa)5 (tfa = CF3COO–; tfaH = CF3COOH) 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 Rb2Mg2(tfa)6­(tfaH)2­·3H2O was restricted to four-metal building blocks. In contrast, RbCa­(tfa)3 and RbSr2(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 Rb2Mg2(tfa)6­(tfaH)2­·3H2O and RbCa­(tfa)3 under inert atmosphere yielded crystalline RbMgF3 and RbCaF3, 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 Rb2Mg2(tfa)6­(tfaH)2­·3H2O provided access to the hexagonal and cubic polymorphs of the fluoroperovskite RbMgF3, respectively. Findings reported in this article highlight that bimetallic trifluoroacetates offer unique features from the standpoint of both crystal lattice topology and reactivity.