Tungsten Fluorides: Syntheses and Electrochemical Characterization in the FLINAK Molten Salt Eutectic

The following tungsten fluorides have been synthesized by simple addition reactions 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 voltammetry in the molten
FLINAK eutectic melt (46.5, 11.5, and 42.0 mol % of LiF, NaF, and KF, respectively) at 475−800 °C. 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) Å, b = 5.7360(11) Å, c = 11.723(2) Å, and Z =
4. Crystals of K3WF6 were cubic, space group Fm3̄ (No. 225) with a = b = c = 8.9160(10) Å, Z = 4.
Electrodeposition of tungsten metal on Pt from FLINAK, prepared by the addition of WF6 gas and metallic
tungsten to the melt, is suggested to result from reduction of an equilibrium mixture of WF83- and WF63-.

研究人员通过简单加成反应，或在高温下以金属钨为还原剂，成功合成了以下氟化钨类化合物：KWF7、K₂WF8、MWF6（M=K、Na、Rb、Cs）、K₂WF7、M₃WF8（M=K、Na、Rb）以及K₃WF6。
采用拉曼光谱（Raman spectra）与循环伏安法（cyclic voltammetry），对上述化合物在475~800 ℃的FLINAK共晶熔盐（FLINAK，其组成为摩尔分数46.5% LiF、11.5% NaF与42.0% KF）中进行了表征。
本研究报道了两种新型化合物K₂WF7与K₃WF6的X射线晶体结构（X-ray crystal structures）。其中，K₂WF7的晶体属于正交晶系，空间群为Pnma（编号62），晶胞参数为a=9.800(2) Å、b=5.7360(11) Å、c=11.723(2) Å，晶胞内化学式单元数Z=4。
K₃WF6的晶体为立方晶系，空间群为Fm-3（编号225），晶胞参数a=b=c=8.9160(10) Å，Z=4。
通过向FLINAK熔盐中加入六氟化钨（WF6）气体与金属钨制备得到的体系中，可在铂基底上电沉积金属钨，该过程被认为源自WF₈³⁻与WF₆³⁻的平衡混合物的还原反应。