Synthesis and crystal structure of two tin fluoride materials: NaSnF 3 (BING-12) and Sn 3F 3PO 4

A new compound, sodium tin trifluoride (NaSnF ₃, which we denote BING-12 for SUNY at Binghamton, Structure No. 12), was synthesized solvothermally from a pyridine-water solvent system. The new compound crystallized in the monoclinic space group C2/ c (No. 15), with a=11.7429(12) Å, b=17.0104(18) Å, c=6.8528(7) Å, β=100.6969(2)°, V=1345.1(2) Å ³ and Z=16. The layered structure consists of outer pyramidal SnF ₃ units, where the fluorides surround a central layer of six- and seven-coordinate sodium atoms. The layers are stabilized by charged Na ⁺ galleries that reside in the center of the layers. Tin trifluorophosphate (Sn ₃F ₃PO ₄, Compound 2) was isolated from a related synthetic system, and crystallized in the rhombohedral space group R3 (No. 146), with a=11.8647(11) Å, c=4.6291(6) Å, V=564.34(10) Å ³ and Z=3. The framework is made up of helical -Sn-F- chains, which are connected by phosphate groups. The materials were characterized by powder X-ray diffraction (PXRD), variable temperature PXRD (VT-PXRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).