The effect of complexing anions on the formation of polynuclear hydroxocomplexes of Cr(III) in aqueous solution

The effect of anions on the hydrolysis of cations with the formation of polynuclear hydroxocomplexes was investigated by applying a complex mixture of physical-chemical methods including dialysis, ultrafiltration, centrifugation, pH-metric titration, method of radioactive indicators and spectrophotometry. A series of anions chosen for investigation included iodide, iodate, phosphate, oxalate, and EDTA.It has been shown that the effect of the anions on the formation of polynuclear hydroxocomplexes of chromium(III) depends on the stability of their complexes with Cr3+-cation. Thus, the iodide-anion, formed weak complexes with Cr3+-cations, but did not interact with polynuclear hydroxocomplexes of chromium(III) under all conditions investigated. The effect of IO3−, SO42− and PO43−-anions was that they did not decrease the total content of polynuclear hydroxocomplexes in solution and, at the same time, were able to join chromium(III) polynuclear hydroxocomplexes, causing the formation of bigger particles precipitated by centrifugation. The effect of oxalate- and EDTA-anions was determined by their high complexing ability with respect to Cr3+-cations. The anions were able to hinder the formation of polynuclear hydroxocomplexes and to decrease their content in solution such that the polymerization reaction was stopped.