Potassium heptafluoroniobate
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| Names | |
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| IUPAC name
Dipotassium heptafluoroniobium[1]
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.037.246 |
| EC Number |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| F7K2Nb | |
| Molar mass | 304.0918 g·mol−1 |
| 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 [77 °F], 100 kPa).
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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.[3]
Synthesis and structure
[edit]The salt is prepared by dissolving niobium pentoxide in a solution of potassium bifluoride in 40% hydrofluoric acid:[4]
- Nb2O5 + 4 KHF2 + 6 HF → 2K2NbF7 + 5 H2O
Potassium heptafluoroniobate and potassium heptafluorotantalate are isostructural. The anion has approximate C2v symmetry, being a face-capped trigonal prism. The Nb-F distances fall in the range 1.940--1.978 Å.[5]
Spectroscopic measurements indicate that the heptafluoride converts to the hexafluoride in solution.[6]
References
[edit]- ^ a b "Niobium potassium fluoride". pubchem.ncbi.nlm.nih.gov. Retrieved 22 May 2024.
- ^ "POTASSIUM HEPTAFLUORONIOBATE(V) | F7K2Nb | ChemSpider". www.chemspider.com. Retrieved 22 May 2024.
- ^ 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.
- ^ W. Kwasnik (1963). "Potassium Heptafluoroniobate (V)". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2pages=255. NY,NY: Academic Press.
- ^ 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.
- ^ 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.