Metal cation binding to acetylenic tetrathiafulvalene–pyridine conjugates: affinity tuned by preorganization and cavity size

A series of three structurally related mono-, bidentate and macrocyclic TTF-pyridine hosts were prepared and titrated with several metal cations including Ag+ and Pb2+ and studied using NMR- and UV–vis spectroscopy and cyclic voltammetry. For Ag+, we found an eightfold increase in binding affinity between the bidentate and macrocyclic host and conversely, for Pb2+, a 100-fold drop. Density functional theory (DFT) calculations support the increased binding affinity for Ag+ is due to an N⋯N distance for the uncomplexed macrocycle very much suited for binding of Ag+ but being too small for Pb2+. The bidentate host, on the other hand, is of a suitable size for Pb2+. [Display omitted]