A Demonstration of Anion Templation and Selectivity in Pseudorotaxane Formation We thank the EPSRC and the University of Reading for funds for the Image Plate System and the Natural Sciences and Engineering Research Council of Canada for financial support to Dr. Wisner.

First- and second-sphere coordination of a chloride anion templates the formation of a [2]pseudorotaxane (see picture) in which a pyridinium diamide threads through the annulus of a macrocyclic isophthalamide wheel. The formation of the pseudorotaxane depends on the nature of the anion involved: the use of a larger anion destabilizes the entire recognition motif.