Secondary hierarchical complexity in double-stranded cluster helicates covered by NNNNN type pincer ligands.

We designed and synthesized a new tripyridine dipyrrolide pincer ligand, which could be doubly deprotonated to provide five-nitrogen-donor sites and then utilized to prepare a subnanometric chiral silver cluster. The cluster belongs to an S 4 point group and shows a double-stranded helicate. DFT calculations were performed to analyze the electronic structure of the cluster. Interestingly, through hierarchical intercluster interactions, the cluster helicates evolve into complex secondary structures including a right-handed helix and a folded sheet, both of which are reminiscent of secondary structures of proteins, i.e. , an α-helix and an antiparallel β-sheet.