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Potassium heptafluoroniobate

Names
IUPAC name Dipotassium heptafluoroniobium
Identifiers
CAS Number	16924-03-1
3D model (JSmol)	Interactive image
ChemSpider	26470453
ECHA InfoCard	100.037.246
EC Number	240-987-7
PubChem CID	44890706
CompTox Dashboard (EPA)	DTXSID30276574
InChI InChI=1S/7FH.2K.Nb/h7*1H;;;/q;;;;;;;2*+1;+5/p-7Key: FTPUNAWAGWERLA-UHFFFAOYSA-G
SMILES F(F)(F)(F)(F)(F)F..
Properties
Chemical formula	F7K2Nb
Molar mass	304.0918 g·mol
Appearance	white solid
Melting point	735 °C (1,355 °F; 1,008 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

Potassium heptafluoroniobate is the inorganic compound with the formula K₂NbF₇. A white water-soluble salt, it is one of the more important fluorides of niobium. It is often invoked as an intermediate in the separation of niobium from tantalum. These two elements are generally found together in ores (e.g. columbite) and their separation presents a challenge since they form very similar compounds. The basis of their separation hinges on the stability and solubility of the fluorides and oxyfluorides. Reduction of this salt gives niobium metal.

Synthesis and structure

The salt is prepared by dissolving niobium pentoxide in a solution of potassium bifluoride in 40% hydrofluoric acid:

Nb₂O₅ + 4 KHF₂ + 6 HF → 2K₂NbF₇ + 5 H₂O

Potassium heptafluoroniobate and potassium heptafluorotantalate are isostructural. The anion has approximate C_2v symmetry, being a face-capped trigonal prism. The Nb-F distances fall in the range 1.940--1.978 Å.

Spectroscopic measurements indicate that the heptafluoride converts to the hexafluoride in solution.

References

1. ^ "Niobium potassium fluoride". pubchem.ncbi.nlm.nih.gov. Retrieved 22 May 2024.
2. "POTASSIUM HEPTAFLUORONIOBATE(V) | F7K2Nb | ChemSpider". www.chemspider.com. Retrieved 22 May 2024.
3. Matthiesen, F.; Christensen, E.; von Barner, J. H.; Bjerrum, N. J. (1996). "The Redox Chemistry of Niobium(V) Fluoro and Oxofluoro Complexes in LiF-NaF-KF Melts". Journal of the Electrochemical Society. 143 (6): 1793–1799. Bibcode:1996JElS..143.1793M. doi:10.1149/1.1836906.
4. W. Kwasnik (1963). "Potassium Heptafluoroniobate (V)". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2pages=255. NY,NY: Academic Press.
5. Brown, G. M.; Walker, L. A. (1966). "Refinement of the structure of potassium heptafluoroniobate, K₂NBF₇, from neutron-diffraction data". Acta Crystallographica. 20 (2): 220–229. Bibcode:1966AcCry..20..220B. doi:10.1107/s0365110x66000458.
6. Keller, O. L. (1963). "Identification of Complex Ions of Niobium(V) in Hydrofluoric Acid Solutions by Raman and Infrared Spectroscopy". Inorganic Chemistry. 2 (4): 783–787. doi:10.1021/ic50008a029.

• Fluoro complexes
• Niobates
• Potassium compounds
• Fluorometallates