Morphological control of heteroleptic cis- and trans-Pd2L2Lʹ2 cages

Abstract

Control over the integrative self-sorting of metallo-supramolecular assemblies has recently generated significant interest as it opens up possibilities of introducing increased complexity and function into a single self-assembled architecture. Here, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd2L2Lʹ2]4+ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd2L2Lʹ2]4+ cage while the same reaction with two ligands bearing bite angles of 75° and 60° forces an anti-conformation for latter ligand, leading to an unprecedented, self-penetrating structural motif; a trans-[Pd2(anti-L)2Lʹ2]4+ heteroleptic cage bearing a “doubly-bridged figure-eight” topology. Each heteroleptic assembly can be accessed through cage-to-cage conversion of their homoleptic precursors, and notably, morphological control of [Pd2L2Lʹ2] cages is achieved through selective ligand displacement transformations in a system of three ligands and at least six possible cage products.