Morphological Control of Heteroleptic cis- and trans-Pd₂L₂L′₂ Cages

Control over the integrative self-sorting of metallo-supramolecular assemblies opens up possibilities for introducing increased complexity and function into a single self-assembled architecture. Herein, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd₂L₂L′₂]⁴⁺ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd₂L₂L′₂]⁴⁺ cage while the same reaction with two ligands with bite angles of 75° and 60° gives an unprecedented, self-penetrating structural motif; a trans-[Pd₂(anti-L)₂L′₂]⁴⁺ heteroleptic cage with a “doubly bridged figure eight” topology. Each heteroleptic assembly can be formed by cage-to-cage conversion of the homoleptic precursors and morphological control of [Pd₂L₂L′₂] cages is achieved by selective ligand displacement transformations in a system of three ligands and at least six possible cage products.