A detailed Pt-195 NMR study of the distribution of Pt(IV) complex species resulting from the aquation of H2PtCl6, H2PtBr6, and mixtures of H2PtCl6/H2PtBr6 in water/dilute HClO4 has been carried out to obtain an understanding of the speciation in these solutions as relevant to the recovery of Pt(IV) complexes from process solutions. A species distribution plot of the [PtCl6](2-), [PtCl5(H2O)](-), and [PtCl4(H2O)(2)] shows that in equilibrated, relatively concentrated H2PtCl6 solutions ([Pt](t) > 0.12 M), the [PtCl4(H2O)(2)] species is below the Pt-195 NMR detection limit; for [Pt](t) concentrations < 0.1 M, the relative concentrations of the [PtCl5(H2O)](-) and [PtCl4(H2O)(2)] species increase significantly, as a result of relatively rapid aquation of the [PtCl6](2-) and [PtCl5(H2O)]-complexes under these conditions. From this Pt-195 NMR data the aquation constants of [PtCl6](2-) and [PtBr6](2-) of log K-6 approximate to 1.75 +/- 0.05 and log K-6 approximate to 2.71 +/- 0.15, respectively, have been determined at 30 degrees C. In mixtures of H2PtCl6/H2PtBr6 in water, a number of previously unidentified aquated complexes of the general formula [PtCl5-nBrn(H2O)](-)(n = 0-5) could be identified, including the possible geometrical isomers of these complexes. These Pt-195 NMR assignments were confirmed by remarkably systematic, linear relationships between the Pt-195 chemical shift increments induced by substitution of Cl- ions by n Br- ions in [PtCl6-nBrn](2)-and [PtCl5-nBrn(H2O)]-complexes. Preferential extraction of the [PtX6](2-) (X = Cl, Br, or a mixture of the two halides) species over their corresponding aquated [PtX5(H2O)]-counterparts by silica-based diethylenetriamine anion exchangers could be demonstrated by means of Pt-195 NMR spectroscopy.