Tuning Reactivity of Platinum(II) Complexes

Absorbance
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
3 4 5 6 7 8 9 10
Figure 6.1: UV-Vis spectrophotometric titration curve of Pt3 with NaOH in the pH range
2-9, I = 1.0 M (NaClO4), T = 25 °C. Inset: plot of Absorbance vs pH at 280 nm.
When the UV-Vis data was fitted using a non-linear least squares procedure, as
represented by the inset in Figure 6.1, and Figures S6.17 and S6.21 for the
corresponding data for the Pt1 and Pt2 complexes (Appendix 6), the pKa values for the
deprotonation of the coordinated aqua molecules were obtained from the standard
Boltzmann equation. The data gave an excellent fit for a system with two dissociation
steps with equilibrium constants Ka1 and Ka2, for which the overall process can be
presented by the reaction given in Scheme 6.2.
Y
H O Pt N
2 N Pt H O 2
H O Pt N
2 N Pt OH
Y
4+
3+
K a1 /OH -
-H 2 O
K a2 /OH -
-H 2 O
10
pH
H Pt N
2O N Pt OH
HO
Pt N
Y
Y
3+
2+
N Pt OH
Scheme 6.2: Summary of the stepwise deprotonation of the dinuclear Pt(II) complexes
as function of pH
λ = 280 nm