Table 1.
Association constants (Ka, M–1) of 2 and 3 fit to a 1:1 binding model.
| Anion | 1 | 2 | 3 |
|---|---|---|---|
| Cl– | – | (2.60±0.45)×102 | (4.0±0.2)×101 |
| Br– | – | (6.0±0.1)×101 | (5.0±0.6)×101 |
| I– | – | – c | (6.0±0.4)×101 |
| H2PO4– | (7.80±2.0)×104a | (4.60±0.00 45)×104b | (3.10±0.32)×103 |
| HSO4– | – | (3.30±0.50)×102 | (1.00±0.09)×102 |
| OAc– | – | (2.60±0.23)×103d | (2.30±0.34)×103 |
Value previously reported.
Association constant obtained from UV/Vis titrations.
Evidence exists for binding, but reliable association constants could not be determined.
Represents an apparent association constant obtained from fitting to a 1:1 model; however, a 1:2 model gave considerably better fits, although high errors and negative Ka values prevented report of this binding data and indicates that neither model appropriately reflects the solution stoichiometry. Association constants represent an average of at least three titrations with various anions added as the tetrabutylammonium salts in 10% DMSO/CHCl3 (or the perdeutero-equivalent for NMR titrations) at 298 K, and were determined using HypNMR 2006 or Hyperquad 2006. Table 3 contains revised values for Ka's with receptor 1 based on the refitting previous data using receptors 2 and 3 as model systems.