Tuning Reactivity of Platinum(II) Complexes

of the σ-electron donating methyl groups 31 that could be associated with a decrease in
the electrophilicity of the platinum atom, but is little influenced by the position to which
they are attached to the pyrazine ligand.
4.3.2 Acid-base equilibria of the diaqua complexes
The representative spectral changes recorded during the pH titration with NaOH are
shown in Figure 4.3 for the diaqua 2,5pzn complex (also Figures S4.2 – S4.4 for the
corresponding data for the pzn, 2,3pzn and 2,6pzn, appendix). The pKa of the
coordinated water molecules were determined by plotting absorbance at a specific
wavelength as a function of pH. A typical example is presented as an inset in Figure 4.3.
Figure 4.3: UV-Visible spectra for the titration of 0.1 mM 2,5pzn with NaOH as a
function of pH in the range 1 to 10 at I = 0.1 M (NaClO4) and T = 298.15
K. Inset: Plot of absorbance versus pH at 297 nm for 2,5pzn.
All the diaqua complexes exhibited two inflection points an indication of two pH
dependent deprotonation steps with equilibrium constants Ka1 and Ka2 as shown in
reaction Scheme 4.1.
13