Tuning Reactivity of Platinum(II) Complexes

H2O-Pt-L-Pt-OH2
H2O-Pt-L-Pt-OH2
H2O-Pt-L-Pt-OH
H2O-Pt-L-Pt-OH
4+
3+
Ka1 Ka1
H + H +
Ka2 Ka2
H + H +
14
H2O-Pt-L-Pt-OH
H2O-Pt-L-Pt-OH
HO-Pt-L-Pt-OH
where, L = pzn, 2,6pzn, 2,3pzn, 2,5pzn
3+
2+
+ H2O H2O
+ H2O H2O
Scheme 4.1: Proposed stepwise deprotonation for the pH dependence of the
dinuclear Pt(II) complexes.
The resulting pKa values for the coordinated water molecules were obtained by fitting
the data, for all the dinuclear complexes, to a standard Boltzmann equation describing
two pKa values using Origin 5.0 ® 28 software. The data obtained are summarised in Table
4.2 and included for comparison are the pKa values for related trans-complexes. 32
Table 4.2: Summary of pKa values for the deprotonation of platinum-bound water in the
[{ cis–PtOH2(NH3)2}2–µ–pzn] 4+ complexes, I = 0.1 M HClO4, T = 298.15 K.
pKa1
pKa2
pzn 2,3pzn 2,5pzn 2,6pzn
3.32 ± 0.06
(3.59 ± 0.33) a
5.64 ± 0.09
(4.36 ± 0.30) a
3.98 ± 0.02
(3.66 ± 0.11) a
6.01 ± 0.18
(4.61 ± 0.22) a
3.96 ± 0.12
(3.68 ± 0.26) a
6.13 ± 0.05
(4.62 ± 0.21) a
3.48 ± 0.51
6.88 ± 0.04
∆pKa 2.32 2.03 2.17 3.40
a pKa values for [{trans–Pt(NH3)2(OH2)}2–μ–pzn] 4+ complexes extracted from
reference. 31