Chiral Metal Self‐Assemblies of Zirconium‐Tetrahedra and Their Second Harmonic Generation Activity

Abstract

AbstractThe chirality of metal‐organic cages holds enormous potential for novel applications in diverse fields, while it is relatively rare to employ such asymmetric units for the construction of noncentrosymmetric materials. Herein, by self‐assembling the 4,4′,4′′‐nitrilotribenzoic acid (H3NBA) with bis(cyclopentadienyl)‐zirconium dichloride (Cp2ZrCl2, Cp=η5‐C5H5) in different solvent conditions, we have obtained three hierarchical packing modes of metallo‐tetrahedra with distinct spatial symmetry groups (designated as Zr‐α, Zr‐β, and Zr‐γ). Among them, Zr‐α employs a simple cubic arrangement and is a common centrosymmetric superstructure, which consists of a pair of equimolar metallo‐tetrahedra enantiomers in its unit cell. While Zr‐β results in conglomerates with spontaneous resolution without using any resolving agents, giving rise to two enantiopure entities separately (Zr‐β‐P, Zr‐β‐M). More importantly, Zr‐γ breaks the inversion center of symmetry and crystallizes into a racemic yet non‐centrosymmetric superstructure with face‐centered cubic packing mode. Based on the non‐centrosymmetric nature, the hierarchical superstructure Zr‐γ displayed good second harmonic generation activities. This work presents a successful instance wherein the reaction solvent induces the modulation of intermolecular packing mode to afford non‐centrosymmetric solid materials, which can greatly promote the development of noncentrosymmetric solid (NCS) materials.