Synthesis and characterization of solvated trifluoroacetate alkaline earth derivatives

The synthesis and characterization of the trifluoroacetic acid (H-TFA) derivatives of a series of alkaline earth congeners was undertaken through the dissolution of the alkaline earth (AE) metal in H-TFA. After drying, the resulting reaction powders were independently crystallized from Lewis basic solvents [pyridine (py) or tetrahydrofuran (THF)] as diverse AE-TFA derivatives. For the smallest cation, an octahedrally bound monomer Mg(TFA)2(py)4 (1) was isolated, wherein the TFA ligands were all terminally (TFA) bound. The remaining compounds were found to adopt polymeric structures with: only bridging (μ-TFA) ligands for {[Ca2(μ-TFA)3(THF)4](μ-TFA)}n (2); a mixture of μ-TFA and chelating bridging (μc-TFA) ligands in {[(μ-TFA)2Sr(μc-TFA)][H-py]py}n (3); and only μc-TFA ligands for {[Ba(μc-TFA)2(μc-TFA)(py)][H-py]}n (4) structure. The later two structures were solved with a pyridinium salt located in the lattice. The trend observed for the TFA ligand was that as the cation increases in size, the ligands transform from bridging to chelating bridging due to the increased coordination sphere of the metals. Elemental analyses, solid-state, and solution multinuclear NMR, and FTIR data confirm the bulk powders were consistent with the X-ray structures.

Graphical abstractA series of alkaline earth trifluoracetic acid (TFA) derivatives were crystallographically characterized as: Mg(TFA)2(py)4 (1), {[Ca2(μ-TFA)3(THF)4](μ-TFA)}n (2), {[(μ-TFA)2Sr(μc-TFA)][H-py]py}n(3); and {[Ba(μc-TFA)2(μc-TFA)(py)][H-py]}n (4) (shown). Elemental analyses, solid-state, and solution multinuclear NMR, and FTIR data confirms the bulk powders were consistent with the X-ray structures.Figure optionsDownload full-size imageDownload as PowerPoint slide