EQUILIBRIA, KINETICS AND MECHANISM FOR COMPLEX-FORMATION BETWEEN HYDROGEN SULFATE SULFATE AND PALLADIUM(II) - HYDROLYSIS OF TETRAAQUAPALLADIUM(II)/

Spectrophotometric equilibrium measurements indicate formation of the complexes [Pd(H2O)(3)HSO4](+) and [Pd(H2O)(3)SO4] in the reaction betw een [Pd(H2O)(4)](2+) and hydrogen sulfate/sulfate in the region: 0.10 less than or equal to [H+] less than or equal to 0.80 M. The stability constants are 0.7 +/- 0.2 and 19 +/- 6 M-1, respectively, at 25 degre es C and 1.00 M ionic strength. The protolysis constant for coordinate d hydrogen sulfate, i.e. the equilibrium constant for the reaction [Pd (H2O)(3)HSO4](+) +H2O reversible arrow[Pd(H2O)(3)SO4] + H3O+, is 2.5 /- 1.0 M. The stability constant for [Pd(H2O)(3)HSO4](+) and the proto lysis constant for coordinated HSO4- are also derived from kinetic mea surements as 0.6 +/- 0.2 M-1 and 2.3 +/- 1.3 M, respectively. The kine tics for the reversible complex formation reaction, studied by use of stopped-flow spectrophotometry, is first order with respect to palladi um complex and total concentration of sulfate, [S(VI)], with an observ ed pseudo-first-order rate constant k(obsd) = k(f)[S(VI)] + k(r) for e xcess sulfate. Here k(f) and k(r) denote observed forward second-order and reverse first-order rate constants, respectively. The kinetic dat a are interpreted in terms of a reaction mechanism which involves para llel and reversible reactions between [Pd(H2O)(4)](2+) and HSO4- and S O42-, respectively, and between [Pd(H2O)(3)OH](+) and HSO4-. Forward a nd reverse rate constants for complex formation between [Pd(H2O)(4)](2 +) and HSO4- are 119 +/- 6 M-1 s(-1) and 210 +/- 60 s(-1) at 25 degree s C, indicating that HSO4- has a similar nucleophilicity as other oxyg en-donor ligands. The rate constants for the reactions of [Pd(H2O)(4)] (2+) with SO42- and of [Pd(H2O)(3)OH](+) with HSO4- cannot be resolved because of a proton ambiguity. The mononuclear protolysis constant of [Pd(H2O)(4)](2+) is pK(h) = 3.0 +/- 0.1 at 25 degrees C and 1.00 M io nic strength as determined from rapid spectrophotometric equilibrium m easurements.