Chromium(II) sulfate

Chromium(II) sulfate is an inorganic compound with the chemical formula CrSO₄. It often comes as hydrates CrSO₄·nH₂O. Several hydrated salts are known. The pentahydrate CrSO₄·5H₂O is a blue solid that dissolves readily in water. Solutions of chromium(II) are easily oxidized by air to Cr(III) species. Solutions of Cr(II) are used as specialized reducing agents of value in organic synthesis.^[1]

Chromium(II) sulfate

Crystalline sample wet with ethanol
Structure of chromium(II) sulfate pentahydrate (CrSO4·5H2O)   Chromium, Cr   Sulfur, S   Oxygen, O   Hydrogen, H
Names
IUPAC name Chromium(2+) sulfate
Other names chromous sulfate, chromous sulphate
Identifiers
CAS Number	13825-86-0 (anhydrous) 15928-77-5 (pentahydrate) 19512-13-1 (trihydrate)
3D model (JSmol)	anhydrous: Interactive image pentahydrate: Interactive image
ChemSpider	55589 (anhydrous)
PubChem CID	61686 (anhydrous)
UNII	Y0C99N5TMZ (anhydrous) Y 990MUV05EC (pentahydrate) Y
CompTox Dashboard (EPA)	DTXSID80160555
InChI Key: RYPRIXSYXLDSOA-UHFFFAOYSA-L Key: RYPRIXSYXLDSOA-NUQVWONBAQ
SMILES anhydrous: [Cr+2].[O-]S(=O)(=O)[O-] pentahydrate: [OH2+][Cr-3]([OH2+])([OH2+])([OH2+])O(S(=O)(=O)[O-]).O
Properties
Chemical formula	CrSO4 (anhydrous) CrSO4·5H2O (pentahydrate)
Molar mass	148.05 g/mol (anhydrous) 238.13 g/mol (pentahydrate)
Appearance	Blue crystalline solid (pentahydrate)
Solubility in water	21 g/(100 mL) (0°C, pentahydrate)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The salt is produced by treating chromium metal with aqueous sulfuric acid:^[2]

Cr + H₂SO₄ + 5 H₂O → CrSO₄·5H₂O + H₂

It can be produced through the reaction of sulfate salts and chromium(II) acetate^[3] or, for in situ use, the reduction of chromium(III) sulfate with zinc.^[1]

Structure

In aqueous solutions chromium(II) sulfate forms metal aquo complexes, presumably with six water ligands. The structures of the crystalline salts are similar to the corresponding hydrates of copper(II) sulfate: pentahydrate, trihydrate, monohydrate, and anhydrous derivatives of chromous sulfate are known. In all of these compounds, the Cr(II) centre adopts octahedral coordination geometry, being coordinated to six oxygen centers provided by a combination of water and sulfate ligands.^[4][5]

References

1. A. Zurqiyah and C. E. Castro "Reduction of Conjugated Alkenes With Chromium(II) Sulfate: Diethyl Succinate" Organic Syntheses, Vol. 49, p.98 (1969).doi:10.15227/orgsyn.049.0098
2. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 2. p. 1365.
3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
4. Hitchman, Michael A.; Lichon, Michael; McDonald, Robbie G.; Smith, Peter W.; Stranger, Robert (1987). "Crystal and Molecular Structure of Chromium(II) Sulfate Pentahydrate and Single-Crystal Electronic Spectra and Bonding of CrSO₄·5 H₂O, Copper Sulfate Pentahydrate and CuSO₄·5 D₂O". Journal of the Chemical Society, Dalton Transactions: 1817–22. doi:10.1039/DT9870001817.
5. Dahmen, T.; Glaum, R.; Schmidt, G.; Gruehn, R. (1990). "Zur Darstellung und Kristallstruktur von CrSO₄·3H₂O" [Preparation and Crystal Structure of Chromium(2+) Sulfate Trihydrate]. Zeitschrift für Anorganische und Allgemeine Chemie. 586: 141–8. doi:10.1002/zaac.19905860119.