Chromium(II) sulfate refers to inorganic compounds with the chemical formula CrSO4(H2O)x. Several closely related hydrated salts are known. The pentahydrate 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.
The salt is produced by treating chromium metal with aqueous sulfuric acid:
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.
^Hitchman, Michael A.; Lichon, Michael; McDonald, Robbie G.; Smith, Peter W.; Stranger, Robert "Crystal and molecular structure of chromium(II) sulfate pentahydrate and single-crystal electronic spectra and bonding of CrSO4.5H2O, copper sulfate pentahydrate and CuSO4.5D2O" Journal of the Chemical Society, Dalton Transactions 1987, pp. 1817-22. doi:10.1039/DT9870001817
^Dahmen, T.; Glaum, R.; Schmidt, G.; Gruehn, R. "Preparation and crystal structure of chromium(2+) sulfate trihydrate" Zeitschrift fuer Anorganische und Allgemeine Chemie 1990, volume 586, pp. 141-8. doi:10.1002/zaac.19905860119