Table 2.
Gibbs free energy values calculated for the dissociation equilibrium of the studied aquo complexes (ΔG°A-H2O(aq)) in kJ mol−1, and pKa values for the associated protonations, obtained directly (pKa1) and with the isodesmic method (pKa2). All data calculated by B3LYP/cc-pVDZ (T = 298.15 K). The most favourable spin states were employed; the first number under spin headers refers to non-protonated compound and the second value to the aquo complex or protonated species.
| Species | Spin | ΔG°A-H2O(aq) | Spin | pKa1 | pKa2 |
|---|---|---|---|---|---|
| Fe(III)-PO | 5/2–1/2 | 12.44 | 5/2–1/2 | −47.2 | −60.7 |
| Fe(II)-PO | 2–2 | −5.12 | 2–1 | −31.4 | −45.0 |
| PO-I | 1/2–1/2 | −9.95 | 1/2–1/2 | −4.2 | −17.7 |
| PO-II | 1–1 | −4.53 | 1–1 | 8.5 | −5.0 |