Chromium (III) fluoride
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| __ Cr 3+ __ F - | ||||||||||
| General | ||||||||||
| Surname | Chromium (III) fluoride | |||||||||
| other names |
Chromium fluoride |
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| Ratio formula | CrF 3 | |||||||||
| Brief description |
volatile, green solid with a pungent odor |
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| properties | ||||||||||
| Molar mass | 108.99 g mol −1 | |||||||||
| Physical state |
firmly |
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| density |
3.8 g cm −3 |
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| Melting point |
> 1000 ° C |
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| Vapor pressure |
approx. 20 mbar (20 ° C) |
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| solubility |
poorly soluble in water |
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| safety instructions | ||||||||||
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||
Chromium (III) fluoride is a chemical compound of chromium and is one of the fluorides . In addition to the anhydrous compound, there are also various hydrates .
presentation
Chromium (III) fluoride is obtained by reacting chromium (III) oxide and hydrogen fluoride :
![{\ displaystyle \ mathrm {Cr_ {2} O_ {3} +6 \ HF + 9 \ H_ {2} O \ longrightarrow 2 \ [Cr (H_ {2} O) _ {6}] F_ {3}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1ef3712af809b5bc933f5853326817466358b742)
The anhydrous form is obtained from hydrogen fluoride and chromium (III) chloride :
properties
Chromium (III) fluoride is a green crystalline solid that is insoluble in common solvents , its colored hydrates [Cr (H 2 O) 6 ] F 3 and [Cr (H 2 O) 3 ] F 3 · 3 H 2 O but are water soluble. The trihydrate is green, the hexahydrate is purple. The anhydrous compound sublimes at 1100-1200 ° C. Like almost all chromium (III) compounds, chromium (III) fluoride has octahedral chromium centers. In the anhydrous form, the six coordination sites are occupied by fluorine . In the hydrates, some or all of the ligands are replaced by water. The aqueous solution of hydrates reacts strongly acid, and from 60 ° C start the crystal dehydration of hydrates.
Anhydrous chromium (III) fluoride crystallizes trigonal , space group R 3 c (space group no. 167) with the lattice parameters a = 4.986 Å and c = 13.21 Å. The trihydrate crystallizes trigonal in the space group R 3 m (No. 166) with the lattice parameters a R = 5.668 Å and α R = 112.5 ° and one formula unit per unit cell. The pentahydrate crystallizes orthorhombically in the space group Pbcn (No. 60) with the lattice parameters a = 10.396 Å, b = 8.060 Å and c = 7.965 Å as well as four formula units per unit cell.
use
Chromium (III) fluoride relative finds little use, such as a corrosion inhibitor in anticorrosion paints, for the pickling of wool and cellulose fibers and dyeing with mordant dyes.
Individual evidence
- ↑ a b c d e f g h i Entry on chromium (III) fluoride in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
- ↑ Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger: Chromium Compounds in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005; doi : 10.1002 / 14356007.a07_067 .
- ^ NN Greenwood, A. Earnshaw: Chemistry of the elements , 1st edition, VCH, Weinheim 1998, ISBN 3-527-26169-9 , p. 1312.
- ↑ a b Frank H. Herbstein, Moshe Kapon, George M. Reisner: Crystal structures of chromium (III) fluoride trihydrate and chromium (III) fluoride pentahydrate. Structural chemistry of hydrated transition metal fluorides. Thermal decomposition of chromium (III) fluoride nonahydrate , In: Zeitschrift für Kristallographie , 1985 , 171 (3-4), pp. 209-224; doi : 10.1524 / zkri.1985.171.3-4.209 .
- ↑ J.-E. Jørgensen, WG Marshall, RI Smith: The compression mechanism of CrF 3 . In: Acta Crystallographica , B60, 2004, pp. 669-673, doi : 10.1107 / S010876810402316X .