In all cases except for receptor 1b, the shifts in the resonances attributed to the amide N-H proton and isophthalic C-H proton were fitted to 1:1 host:guest binding model, where the use of the 1:2 host:guest model was found to give a similar K11 value to that obtained by the 1:1 model suggesting that the binding of a second chloride ion is negligible within the chloride concentration range used in the titrations. Within the four different sub-series, the same pattern regarding the strength of binding affinities emerged, corresponding to the identity of the R2 substituents. The receptors containing the naphthalene linkers (1b-4b) had the weakest binding affinities of the series, whilst slightly higher binding affinities were obtained for the unsubstituted phenylene receptors (1a-4a). Notably, compounds 1c-4c containing 4,5-difluorophenylene moieties have binding constants ~2.7-4.5-fold larger than their respective phenylene and naphthalene-containing derivatives. A similar trend appeared for the R1 substituents, generally following electron-withdrawing capability with a general order of NO2 > CF3 > F > t-Bu (1 > 3 > 2 > 4). The receptor with the highest anion binding constant of Ka = 2850 M -1 was receptor 1c, which contained R1 = NO2 and R2 = 4,5difluorophenylene substituents (Table ). The receptor with the weakest binding affinity was compound 4b (R1 = t-Bu and R2 = naphthalene), which aligns with both trends. Limited solubility was observed for the tetralactams containing naphthalene moieties, which can be attributed to the greater tendency for the extended aromatic system to 𝜋-𝜋 stack and form aggregates in solution.