Polynuclear chromium(III) carboxlylates: Part 2. Chromium(III) acetate — whatʹs in it?

Chromium(III) acetate has been widely used in industry for decades. The commercial material is an ill-defined substance, which represents a large number of compounds having different compositions, physical properties and appearances. Several samples of Cr(III) acetate, from various commercial sources were examined by ion-exchange chromatography. All the samples were found to contain several species such as [Cr3O(O2CCH3)6(H2O)3]+ and other positively charged purple complexes. They also contain various amounts of the neutral violet complex [Cr8(OH)8(O2CCH3)16] (1) which crystallizes upon slow evaporation of its aqueous solution. 1 is a cyclic octanuclear complex with hydroxo and acetate ligands bridging the adjacent Cr(III) ions. The structure of a well-defined Cr(III) acetate, namely, [Cr(H2O)6](O2CCH3)3 (2) has been determined crystallographically and its decomposition products were examined by ion-exchange chromatography. Compound 2 decomposes under ambient conditions, releasing acetic acid and water producing neutral and charged polynuclear Cr(III) complexes.