Niobium(V) fluoride

Niobium(V) fluoride, also known as niobium pentafluoride, is the inorganic compound with the formula NbF5. It is a colorless solid.

Preparation and structure
Niobium pentafluoride is obtained by treatment of any niobium compound with fluorine:
 * 2 Nb +  5 F2   →  2 NbF5
 * 2 NbCl5 +  5 F2   →  2 NbF5  +  5 Cl2

As shown by X-ray crystallography, the solid consists of tetramers [NbF5]4. This structure is related to that for WOF4.

Reactions
It reacts with hydrogen fluoride to give H2NbF7, a superacid. In hydrofluoric acid, NbF5 converts to [NbF7]2- and [NbF5O]2-. The relative solubility of K2[MFO] (M = Nb, Ta) is the basis of the Marignac process for separation of Nb and Ta.

NbCl5 forms a dimeric structure (edge-shared bioctahedron) in contrast to the corner-shared tetrameric structure of the fluoride.