Heteromeric Completive Self-Sorting in Coordination Cage Systems.

Heteroleptic coordination cages, nonstatistically assembled from a set of matching ligands, can be obtained by mixing individual components or via cage-to-cage transformations from homoleptic precursors. Based on the latter approach, we here describe a new level of self-sorting in coordination cage systems, namely, 'heteromeric completive self-sorting'. Here, two heteroleptic assemblies of type PdAB and PdAC, sharing one common ligand component A but differing in the other, are shown to coexist in solution. This level of self-sorting can be reached either from a statistical mixture of assemblies based on some ligands B and C or, alternatively, following a first step of integrative self-sorting giving a distinct PdBC intermediate. While subtle enthalpic factors dictate the outcome of the self-sorting, we found that it is controllable. From a unique set of three ligands, we demonstrate the transition from strict integrative self-sorting forming a PdABC cage to heteromeric completive self-sorting to give PdAB and PdAC by variation of the ligand ratio. Cage-to-cage transformations were followed by NMR and MS experiments. Single crystal X-ray structures for three new heteroleptic cages were obtained, impressively highlighting the versatility of ligand A to either form a π-stacked -figure-of-eight arrangement in PdAB or occupy two -edges in PdAC or only a single edge in PdABC. This study paves the way toward the control of heteroleptic cage populations in a systems chemistry context with emerging features such as chemical information processing, adaptive guest selectivity, or stimuli-responsive catalytic action.