Table 2.
Binding and structural data for complexes of 1 with anions.
| Complex | Binding constants from NMR titrations K a [m −1][a] |
DFT binding energy [kcal mol−1] |
Literature ΔG, anion hydration [kcal mol−1]12 |
Urea nitrogen–anion distances [Å][e] |
||
|---|---|---|---|---|---|---|
| Receptor[c] | Single arm[d] | Crystal structure | Molecular model | |||
| 1⋅I− | <5 | −16.1 | −6.3 (−12.6) | −65.7 | – | 3.68 (2), 3.63 (2) |
| 1⋅NO3 − | 10 | −17.7 | −8.5 (−17.0) | −71.7 | 3.00, 3.11, 2.91, 2.98 | 3.07 (2), 2.89 (2) |
| 1⋅Br− | 70 | −16.6 | −7.0 (−14.0) | −75.3 | 3.52, 3.48, 3.54, 3.44 | 3.48 (2), 3.42 (2) |
| 1⋅HSO4 − | 180 | −17.7 | −8.2 (−16.4) | – | – | 2.96 (2), 2.90, 2.91 |
| 1⋅Cl− | 670 | −16.9 | −7.7 (−15.4) | −81.3 | 3.30, 3.43, 3.27, 3.20 | 3.32 (2), 3.25, 3.22 |
| 1⋅AcO− | 40 000 | −22.8 | −13.1 (−26.2) | −87.2 | 2.86 (2), 2.80, 2.74 | 2.81 (2), 2.76, 2.78 |
| 1⋅HCO3 − | 42 000 | −20.2 | −11.7 (−23.4) | −80.1 | – | 2.98, 3.01, 2.93, 2.79 |
| 1⋅H2PO4 − | 46 000 | −22.4 | −9.2 (−18.4) | −111.1 | – | 2.88, 2.86, 2.81, 2.80 |
| 1⋅SO4 2− | >105 [b] | −27.4 | −12.9 (−25.8) | −258.1 | 2.92, 2.93 (2), 2.87 (2), 2.94, 3.01, 3.00 | 2.90 (2), 3.01 (2), 2.98 (2), 3.30, 3.54 |
| 1⋅HPO4 2− | – | −30.6 | −15.2 (−30.4) | – | – | 2.80, 2.75, 2.72, 2.69 |
[a] [D6]DMSO/H2O (200:1). [b] Weaker binding of a second sulfate anion forming 1⋅(SO4 2− )2 was observed. [c] The binding energy was obtained by subtracting the total energies of the optimised anion and transporter from that of the anion–transporter complex in DMSO. [d] The binding energy was obtained by subtracting the total energy of the optimised anion and single arm [methyl(p‐nitrophenyl)urea] from that of the anion–arm complex in DMSO. Doubling these energies gives the values in parentheses, for comparison to the values for the preorganised receptor. [e] Distances from nitrogen atoms to halide anions, or to the nearest oxygen atom of oxoanions. Numbers in brackets refer to the multiplicity of identical distances to different nitrogen atoms.