A series of alkaline-earth β-diketonate complexes derived from 2-thenoyltrifluoroacetone (TTA) and 2-methylimidazole was synthesized to study the influence of the metal ion (Mg2+, Ca2+, Sr2+, Ba2+) on coordination geometry, lattice organization, and thermal behavior. Single-crystal X-ray diffraction reveals that Ca–TTA crystallizes as a seven-coordinate Ca(TTA)3(H2O)− unit with capped trigonal prismatic CaO7 geometry, whereas Sr– and Ba–TTA form eight-coordinate M(TTA)42 – complexes with distorted square-prismatic MO8 environments. The systematic increase in average M–O bond lengths (Ca–O 2.38 Å; Ba–O 2.74 Å) and unit-cell volume reflects expansion of the coordination sphere with increasing ionic radius. In contrast, Mg–TTA yields only microcrystalline material unsuitable for full structural resolution; spectroscopic and powder diffraction data suggest formation of a magnesium β-diketonate framework but without definitive crystallographic assignment. Infrared spectroscopy confirms deprotonation of TTA and consistent bidentate coordination across the series. A pronounced O–H stretching band is observed for Mg– and Ca–TTA, consistent with coordinated water identified crystallographically for Ca–TTA, while N–H bands in the 3150–3100 cm–1 region confirm incorporation of protonated 2-methylimidazolium counterions in all complexes. Thermogravimetric analysis reveals metal-dependent decomposition behavior, where Ca– and Sr–TTA exhibit staged degradation between 180 and 300 °C, Ba–TTA displays more clearly resolved stepwise decomposition at elevated temperatures, and Mg–TTA undergoes substantial early mass loss below 110 °C, indicating the removal of weakly bound, labile components or occluded species. Final residues (23–26%) are consistent with formation of metal-rich inorganic phases, likely oxides and/or carbonates. These results demonstrate how variation in alkaline-earth ionic radius modulates coordination number, lattice stabilization, crystallinity, and thermal response in TTA-based complexes.
Bravo-Arredondo et al. (Tue,) studied this question.