Configurational Control of Low-Symmetry Heteroleptic Metal-Organic Cages with Asymmetric Ligands

Abstract

Low-symmetry metal-organic cages (MOCs) can better mimic the structure of biological enzymes compared to high-symmetry MOCs, due to their unique internal cavities that resemble the specialized and irregular active sites of enzymes. In this study, two low-symmetry heteroleptic MOCs with six Pd(II) centers, Pd6LA6LB6 and Pd6LB6LC6, were successfully constructed by combining two strategies: asymmetric ligand assembly and multi-ligand co-assembly. Crystallographic characterization and analysis revealed that Pd₆LA₆LB₆ is a mixture of potentially 16 isomers. Introducing a methyl group at the ortho position of the coordination site of ligand LC induced steric hindrance, driving Pd₆LB₆LC₆ to undergo a structural transformation and selectively assemble into a single dominant configuration from 13 potential isomers. This work not only demonstrates the immense potential of integrating asymmetric ligand assembly with multi-ligand co-assembly strategies but also highlights the critical role of steric effects in guiding assembly pathways and achieving precise configurational control in low-symmetry MOCs.