Proton dissociation constants (pKa) of HL1, HL2, HL5 and HL1(7), overall stability constants (log β)a and pKa values of their Cu(ii) complexes determined by UV–vis titrations in 30 : 70% (v/v) DMSO/H2O solvent mixture {T = 298 K; I = 0.10 M (KCl)}.
| HL1 | HL2 | HL5 | HL1(7) 30 | |
|---|---|---|---|---|
| pKa1 H2(HL)2+ | 2.07 ± 0.01 | 2.64 ± 0.01 | 2.41 ± 0.01 | 2.32 ± 0.01 |
| pKa2 H(HL)+ | 5.04 ± 0.02 | 4.97 ± 0.02 | 5.55 ± 0.01 | 4.75 ± 0.01 |
| log β [Cu(HL)]2+ | 8.55 ± 0.02 | 9.17 ± 0.02 | 9.57 ± 0.01 | 8.33 ± 0.01 |
| log β [Cu(L)]+ | 4.14 ± 0.02 | 4.06 ± 0.02 | 4.31 ± 0.01 | 4.01 ± 0.01 |
| pKa [Cu(HL)]2+ | 4.41 | 5.11 | 5.26 | 4.32 |
| pKa [Cu(L)]+ | >8 | >8 | >8 | 7.09 |
| log K′ [Cu(L)]+ b | −2.97 | −3.55 | −3.65 | −3.06 |
a
The given error is originated from the fitting of the calculated and the experimental absorbance values in the wavelength range between 260 and 560 nm.
b
K′ refers to the following equilibrium: H2(HL)2+ + Cu2+ ⇌ [Cu(L)]+ + 3H+.