Crystalline sodium heptafluorobutyrate Na(hfb)∞ is isolated form an aqueous solution after interacting sodium carbonate with heptafluorobutyric acid. The structure of the Na(hfb)∞ single crystal is determined at temperatures of 100 K and 300 K. The compound has a layered structure with perfluoroalkyl substituents directed toward the interlayer space. Sodium ions are bridged in layers by carboxylate anions, and each of them additionally coordinates two fluorine atoms. The energies of coordination bonds are estimated in the crystal structure. The anisotropic thermal expansion of the structure is determined by powder X-ray diffraction in the temperature range of 100-400 K. It is shown that phase transitions are absent. The decomposition of Na(hfb)∞ upon heating is studied by TGA-DSC-MS. It is found that at 250-300 °C the decomposion is endothermic with the formation of NaF.
Tsymbarenko et al. (Sun,) studied this question.