Controllable self-assembly of mesomeric metallo-organic helicate and its π-electron number dependent encapsulation of polycyclic aromatic hydrocarbons (PAHs)

Abstract

In the field of metallo-organic helicates, the controlled synthesis of low-symmetric structures remains a significant challenge on the precise control over the self-assembly process due to their thermodynamically disfavored nature, compared to highly symmetric forms. This study introduces an effective strategy by shifting the design focus from ligands to metal centers. Through precise regulation of the stereoconfiguration, two metal centers are directed to adopt opposite handedness, affording a mesomeric and C₁ symmetric helicate structure S, fully characterized by ¹H NMR, ESI-MS and SC-XRD. The resulting helicate structure features a well-defined square cavity with a 8.5 Å distance between roof and floor, is capable of accommodating planar polycyclic aromatic hydrocarbons (PAHs) via π–π stacking interaction within optimal range after slight compression. More importantly, the binding constants shows a proportional enhancement with the increasing of number of π-electrons in PAH guests. This work points toward new direction for developing functional low-symmetric metallo-organic supramolecular assemblies. And, the clear structure-function relationship highlights its potential applications in molecular separation and sensing.