Highly Anisotropic Pd2Lab 2Lcc 2 and Pd2Lab 2Lcd 2 Type Cages by Heteromeric Completive Self-Sorting.

Abstract

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., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low-symmetry Pd2Lab 2Lcd 2-type cage. It was accomplished by high-fidelity integrative self-sorting of two different low-symmetry cages having Pd2Lab 4 and Pd4Lcd 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 Pd2Lab 2Lcd 2-type cage. By taking advantage of the complemental geometries between ligands, a low-symmetry Pd2Lab 2Lcc 2-type cage was also obtained. Heteromeric completive self-sorting of three homoleptic assemblies (Pd2Lab 4, Pd4Lcc 8 and Pd4Lcd 8-type cages) into an exclusive mixture of Pd2Lab 2Lcd 2 and Pd2Lab 2Lcc 2-type mixed ligated assemblies was demonstrated through cage-to-cage transformations.