Self-Sorting of Transient Polymer Networks by the Selective Formation of Heteroleptic Metal-Ligand Complexes

Advances in self-sorting mechanisms have resulted in the development of a broad library of well-defined supra -molecular coordination complexes (SCCs) with unprecedented geometries. These SCCs have promising applications like those in catalysis and solar cells. Moreover, the dynamic nature of coordination bonds allows them to undergo stimuli-responsive topology rearrangements, which are used in a plethora of molecular machines. These advances are, however, rarely employed in the design of metallo-supramolecular polymer networks (MSPNs). To address this gap, we use steric hindrance as a powerful self-sorting mechanism to construct MSPNs based on the selective formation of heteroleptic complexes. We graft tetra-arm poly(ethylene glycol) precursors with sterically demanding 2,9-bis(mesitylene)-1,10-phenanthroline or two slim unsubstituted phenanthroline and terpyridine ligands and study their complexation-induced gel formation. Rheological data disclose that the heteroleptic complexation, which is controlled by the coordination geometry preference of the utilized metal ion, can induce up to 5 orders of magnitude delay in the network relaxation and more than twofold increase in plateau modulus due to the removal of primary loops. The structural/electronic characterization of complexes by density functional theory nicely explains the distinct performance of different metal ions in gel formation. These results open a promising interface between polymer science and coordination chemistry that can ultimately lead to the development of new hybrid materials with exceptional properties and novel stimuli responsiveness.