TaF6 Tantalum fluoride

Copper Tantalum Fluoride, CuF2.TaF6.4H20 or CuTaF7.4H20, can be obtained in blue, transparent, rhombic crystals by the action of copper oxide on a solution of tantalum pentoxide in excess of hydrofluoric acid. It is very readily soluble in water.3... 

TaF6 Tantalum(V) fluoride, 3 179 TeBr6K2 Potassium hexabromo-tellurate(IV), 2 189 TeCl4 Tellurium (IV) chloride, 3 140... 

In summary, it can be said that tantalum-containing fluoride solutions generally consist of two types of ions TaF72 and TaF6. Low acidity of the solution (i.e. low HF concentration) leads to the predominant formation of TaF72 complex ions, while higher concentrations of HF lead to the presence of TaF6" complex ions. 

Table 55 presents the results discussed above. Fluoride melts containing tantalum contain two types of complex ions, namely TaF6 and TaF72 . The equilibrium between the complexes depends on the concentration of fluoride ions in the system, but mostly upon the nature of the outer-sphere cations. The complex ionic structure of the melts can be adjusted by adding cations with a certain polarization potential. For instance, the presence of low polarization potential cations, such as cesium, leads primarily to the formation of TaF72 complexes, while the addition of cations with relatively high polarization potentials, such as lithium or sodium, shifts the equilibrium towards the formation of TaF6 ions. 

In the case of a mixture of hydrofluoric and sulfuric acids, the process is more complex. It can be noted that sulfuric acid most probably interacts mainly with iron and manganese, whereas hydrofluoric acid serves mostly in the dissolution of tantalum and niobium and their conversion into soluble fluoride complexes. Nevertheless, due to the high acidity of the solution, here too the formation of hexafluorotantalate and hexafluoroniobate complex ions, TaF6" and NbF6, is expected. Hence, it is noted that the acid dissolution of tantalum-and niobium-containing raw material leads to the formation of hexafluoro-acids — HTaF6 and HNbF6. 

Kuterev, Stoyanov, Bagreev and Zolotov [461] reported on the investigation, using IR spectroscopy, of the composition of niobium and tantalum complexes extracted by amines from fluoride solutions. It was shown that in solutions that contain hydrofluoric acid in concentrations ranging from 1M to 12M, both niobium and tantalum were extracted in the form of NbF6 and TaF6 ... 

Fluorine forms tantalum pentafluoride, TaF6, which resembles the columbium salt, being known only in solution. It forms important double fluorides. 

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