The edta complex of platinum(IV): a titrimetric and spectrophotometric study

Platinum in the form of hexachloroplatinate(IV) reacts slowly with EDTA in a 1:1 mole ratio. At the concentration level used (a few mg per 50–75 ml), favorable conditions were solution of pH 3–4.5, and 3–8-fold molar excess of EDTA. Complete reaction required heating at 100° for 1.5–2 h. The reaction rate was retarded by acetate ion, but not by nitrate or sulfate. Titrimetric determination of platinum was accomplished by addition of excess standard EDTA, buffering to pH 3–4.5, heating the mixture at 100° for 1.5 h, buffering to pH 5.3 with acetic acid-acetate, and back-titrating with zinc acetate to a xylenol orange end-point. Blank corrections were necessary to compensate for trace metal impurities in the water and/or reagents. Determinations of 0.4–3 mg of platinum per 50 ml were accurate to ± 1.3% standard deviation. Both titrimetric and spectrophotometric evidence ruled out the possibility of reduction of platinum(IV) by EDTA. Titrimetric methods showed the complex to be PtCl₄HY^3-, where Y is the deprotonated EDTA.