Tungsten fluorides: Syntheses and electrochemical characterization in the FLINAK molten salt eutectic

The following tungsten fluorides have been synthesized by simple addition r eactions or by reduction with tungsten metal at elevated temperature: KWF7, K2WF8, MWF6 (M = K, Na, Rb, Cs), K2WF7, M3WF8 (M = K, Na, Rb), and K3WF6. The compounds were characterized by their Raman spectra and by cyclic volta mmetry in the molten FLINAK eutectic melt (46.5, 11.5, and 42.0 mol % of Li F, NaF, and KF, respectively) at 475-800 degreesC. X-ray crystal structures are reported for two new compounds K2WF7 and K3WF6. The crystals of K2WF7 were orthorhombic, space group Pnma (No. 62) with a = 9.800(2) Angstrom, b = 5.7360(11) Angstrom, c = 11.723(2) Angstrom, and Z = 4. Crystals of K3WFs were cubic, space group Fm (3) over bar (No. 225) with a = b = c 8.9160(10 ) Angstrom, Z = 4. Electrodeposition of tungsten metal on Pt from FLINAK, p repared by the addition of WFs gas and metallic tungsten to the melt,is sug gested to result from reduction of an equilibrium mixture of WF83- and WF63 -.