NMR Study of Properties in Solution of Platinum(II) Ammine-Aqua Complexes, Including Determination of Acid Dissociation Constants
Abstract
In view of the interest in cis-Pt(NH3)2Cl2 and its derivatives in recent years, it is remarkable that there are, to our knowledge, no values from reliable experimental determinations in the literature for the acid dissociation constants of such simple species as cis-Pt(NH3)2(H2O)2 2+ (I) and cis-Pt(NH3)2Cl(H2O)+ (II). Grinberg and Ryabchikov (1) reported that, although trans-Pt(NH3)2(H2O)2 2+ with NaOH gave a simple titration curve with two distinct “breaks” corresponding to the two deprotonation steps, the cis isomer (I) gave a much more complex curve which they claimed could give only an average of the two acid dissociation constants. If the data presented by Jensen (2) are plotted, it is clear that he, too, obtained a complex curve, but he nevertheless analysed these data to give values (at 20°C) of pKa1 = 5.56 and pKa2 = 7.32. Perumareddi and Adamson (3) gave no details of their procedure, but reported pKa1 = 5.63 and pKa2 = 9.25. We now know (4,5) that in solutions containing moderate concentrations of cis-Pt(NH3)2(OH)(H2O)+ there is rapid formation of hydroxo-bridged oligomers [Pt(NH3)2(μ-OH)]n n+ (n = 2,3).
Keywords
American Chemical Society Complex Curve Acid Dissociation Constant Chloro Complex Potentiometric DeterminationPreview
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References
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