Highly Anisotropic Pd₂L^ab ₂L^cc ₂ and Pd₂L^ab ₂L^cd ₂ Type Cages by Heteromeric Completive Self-Sorting

Pd(II)-based low-symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., L^aa, L^bb etc.) or only one type of unsymmetrical ligand (e.g., L^ab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., L^ab and L^cd, aiming at a low-symmetry Pd₂L^ab ₂L^cd ₂-type cage. It was accomplished by high-fidelity integrative self-sorting of two different low-symmetry cages having Pd₂L^ab ₄ and Pd₄L^cd ₈-type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non-statistical exclusive self-assembly of the Pd₂L^ab ₂L^cd ₂-type cage. By taking advantage of the complemental geometries between ligands, a low-symmetry Pd₂L^ab ₂L^cc ₂-type cage was also obtained. Heteromeric completive self-sorting of three homoleptic assemblies (Pd₂L^ab ₄, Pd₄L^cc ₈ and Pd₄L^cd ₈-type cages) into an exclusive mixture of Pd₂L^ab ₂L^cd ₂ and Pd₂L^ab ₂L^cc ₂-type mixed ligated assemblies was demonstrated through cage-to-cage transformations.