Acid-base equilibria in aqueous solution of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25 °C, 0.2 M ionic strength. A potentiometric study

Abstract

Acid-base equilibria in aqueous solutions of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25 °C, 0.2 M ionic strength (KNO 3), have been investigated by potentiometry with a glass electrode. The procedure consisted of multiple addition of the investigated analyte to a supporting electrolyte solution (“multiple sample addition”) and subsequent titration with strong base. For the treatment of potentiometric multiple sample addition data, a new linearization procedure, suitable for an acid dissociation equilibrium whose product dimerizes, has been devised and tested. The potentiometric results have been interpreted with the support of NMR data. By dissociation of the first acidic function of the solute diaquo cation, cis-[(PMe 3) 2Pt(OH 2) 2] 2+, a dimeric ampholite, cis-[(PMe 3) 2Pt(μ-OH)] 2 2+, is quantitatively formed which, in turn, can be converted into the di-hydroxo derivative cis-(PMe 3) 2Pt(OH) 2. The two acid dissociation steps involving two molecules of solute and condensation of ampholyte have p K a1(c) = 3.89 and p K a2(c) = 22.17.