Ca- and Sr-tetrafluoroisophthalates: mechanochemical synthesis, characterization, and ab initio structure determination

Abstract

New fluorinated coordination polymers were prepared mechanochemically by milling the alkaline earth metal hydroxides M^II(OH)₂·xH₂O (M^II: Ca, Sr) with tetrafluoroisophthalic acid (H₂mBDC-F₄). The structures of [{Ca(mBDC-F₄)(H₂O)₂}·H₂O] (1) and [{Sr(mBDC-F₄)(H₂O)₂}·H₂O] (2) were determined based on ab initio calculations and their powder X-ray diffraction (PXRD) data. The compounds are isomorphous and crystallize in the orthorhombic space group P2₁2₁2₁. The determined structures were validated by using extended X-ray absorption (EXAFS) data. The new materials were thoroughly characterized using elemental analysis, thermal analysis, magic angle spinning NMR, and attenuated total reflection-infrared spectroscopy. Further characterization methods such as BET, dynamic vapor sorption, and scanning electron microscopy imaging were also used. Our investigations indicate that mechanochemistry is an efficient method for preparing such materials.