Tuning Reactivity of Platinum(II) Complexes

Absorbance
Table 7.2: Summary of pKa values for the deprotonattion steps of aqua platinum(II)
complexes at 25 °C. pKa values of trans-isomers are included for comparison
purposes.
pKa (cis)
b pKa
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
(trans)
200 220 240 260
EnPt PropPt ButPt HexPt OctPt DecPt
-
4.98 ± 0.09
5.34 ± 0.18
5.30 ± 0.12
5.51 ± 0.05
5.50 ± 0.02
a Extracted data from reference 43 and b from reference 26.
Absorbnce
Wavelength (nm)
0.48
0.46
0.44
0.42
0.40
0.38
14
λ = 241 nm
1 2 3 4 5 6 7 8 9 10
Figure 7.3: UV-Vis spectra of the diaqua OctPt complex recorded as a function
of pH in the range of 2- 10; I = 0.10 M (NaClO4), T = 25 ºC. Inset:
Plot of absorbance vs. pH at 241 nm.
6.01 ± 0.03 a
5.62 ± 0.03
5.76 ± 0.03
-
6.22 ± 0.12
Despite the possibility of hydrogen bonding between the aqua/hydroxo groups that
would result after the first deprotonation step due to the cis-orientation and flexibility of
(CH2)n chain of the linker, only one inflection point was detected in the titration curves
of the complexes, indicating that Ka1 ≈ Ka2. 43 Moreover, both the {PtN3O} sites carry a
positive charge (+2) and also the same charge difference (+1) occurs during the
deprotonation steps of the two coordinated water molecules. 43 When these facts are
coupled with the σ-donor ability of the primary amine function on the linker, any
pH
-