Polynuclear chromium(III) carboxlylates Part 2. Chromium(III) acetate - what's in it?

摘要

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 [Cr_3O(O_2CCH_3)_6(H_2O)_3]~+ and other positively charged purple complexes. They also contain various amounts of the neutral violet complex [Cr_8(OH)_8(O_2CCH_3)_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(H_2O)_6](O_2CCH_3)_3 (2) has been determined crystrallographically 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) comploexs.