Template Control over Dimerization and Guest Selectivity of Interpenetrated Coordination Cages

We have previously shown that the self-assembly of dibenzosuberone-based bis-monodentate pyridyl ligands L¹ with Pd^II cations leads to the quantitative formation of interpenetrated coordination cages [BF₄@Pd₄L¹₈]. The BF₄^– anion inside the central cavity serves as a template, causing the outer two pockets to show a tremendous affinity for allosteric binding of two small chloride anions. Here we show that derivatization of the ligand backbone with a bulky aryl substituent allows us to control the dimerization and hence the guest-binding ability of the cage by the choice of the templating anion. Steric constraints imposed by L² prevent the large BF₄^– anion from serving as a template for the formation of interpenetrated double cages. Instead, a single isomer of the monomeric cage [Pd₂L²₄] is formed. Addition of the small anionic template Cl^– permits dimerization, yielding the interpenetrated double cage [Cl@Pd₄L²₈], whose enlarged outer pockets show a preference for the binding of large anions such as ReO₄^–.