Tantalum(V) fluoride
Tantalum fluoride is the inorganic compound with the formula. It is one of the principal molecular compounds of tantalum. Characteristic of some other pentafluorides, the compound is volatile but exists as a tetramer in the solid state.
Preparation and structure
is prepared by treating tantalum metal with fluorine gas.[Niobium(V) fluoride|] is prepared similarly.
Solid and molten is tetrameric, consisting of four octahedral centers linked via bridging fluoride centers. Gaseous is monomeric and adopts the trigonal bipyramidal structure with D3h symmetry.
Reactions and derivatives
The tendency of to form clusters in the solid state indicates the Lewis acidity of the monomer. Indeed, reacts with fluoride sources to give the ions,, and . With neutral Lewis bases, such as diethyl ether, forms adducts.is used in combination with HF as a catalyst for the alkylation of alkanes and alkenes and for the protonation of aromatic compounds. The –HF system is stable in reducing environments, unlike –HF. In the presence of fluoride, tantalum pentafluoride forms the anions,, or, depending on the nature of the counterion and the concentration of HF. High concentrations of HF favor the hexafluoride by virtue of the formation of [bifluoride|]:
The salts have been crystallized. For M = K, the crystals consist of anions together with fluoride that does not coordinate to Ta, and the salt is actually potassium fluoride heptafluorotantalate. For M = Na, the crystals features, and the salt is sodium octafluorotantalate.