Table 3. Hydration State, Mn–17O(Water) Hyperfine Coupling Constant, Mean Water Residency Time at 37 °C, and Enthalpy of Activation for Water Exchange Measured for Mn(II) Complexes in HML and ML Formsa.
| HML |
ML |
|||||||
|---|---|---|---|---|---|---|---|---|
| q | Ao/ℏ (×107 rad/s) | τm310 (ns) | ΔH⧧ (kJ/mol) | q | Ao/ℏ (×107 rad/s) | τm310 (ns) | ΔH⧧ (kJ/mol) | |
| HBET | 1 | 2.51 ± 0.04 | 22 ± 1 | 40.0 ± 0.9 | 1 | 3.54 ± 0.55 | 0.27 ± 0.02 | 33.8 ± 1.5 |
| HBET–OMe | 1 | 2.44 ± 0.04 | 23 ± 1 | 41.2 ± 0.9 | 1 | 4.15 ± 0.98 | 0.28 ± 0.01 | 40.7 ± 1.1 |
| HBET–NO2 | 0.5 | 3.02 ± 0.04 | 2.4 ± 0.1 | 39.9 ± 0.6 | 0.5 | 3.48 ± 0.09 | 2.1 ± 0.1 | 41.2 ± 1.1 |
| CyHBET | 1 | 2.53 ± 0.03 | 8.0 ± 0.2 | 38.4 ± 0.5 | 1 | 3.36 ± 0.99 | 0.13 ± 0.01 | 41.2 ± 3.4 |
| CyHBET–OMe | 1 | 2.46 ± 0.03 | 8.8 ± 0.7 | 38.6 ± 1.5 | 1 | 4.02 ± 0.63 | 0.33 ± 0.02 | 20.7 ± 1.6 |
| CyHBET–NO2 | 1 | 3.75 ± 0.58 | 0.52 ± 0.04 | 30.4 ± 2.3 | 1 | 3.97 ± 0.60 | 0.67 ± 0.02 | 31.3 ± 1.0 |
a
Charges omitted for clarity. Hydration state q = 1 is maintained for all measured HML species. Hydration state remains unchanged upon conversion to ML with the exception of [MnII(HBET–NO2)]2–, which was measured as q = 0.5, which implies a mixture of q = 0 and q = 1 species. Water exchange is accelerated about 3-fold in complexes of the CyHBET–R′ series as compared to HBET–R′.