Regulation of Composition and Chirality of Metallo-Assemblies through Metal Ion Coordination Capability

The chiroptical properties of supramolecular assemblies can be modulated by multiple variables, including ligand geometry, temperature, the constituent anions, and pH. However, the directional influence of metal-ligand bond strength on their structural and functional regulation remains underexplored. This study leverages the self-assembly of a pair of chiral ligands (<i>S</i>-/<i>R</i>-L1) and transition metal ions with distinct coordination capabilities (Zn²⁺, Fe²⁺, Co²⁺, Ni²⁺ vs Cd²⁺, Cu²⁺) to establish the intrinsic mechanism, whereby coordination bond strength governs the composition and circular dichroism (CD) signal of the resulting metallo-assemblies. Experimental measurements have demonstrated that metal ions with strong coordination ability (Zn²⁺, Fe²⁺, Co²⁺, and Ni²⁺) favor tetrameric three-dimensional crown-like structures [(M₄<i>R</i>/<i>S</i>L₄)(PF₆)₈]. Conversely, labile metal ions (Cd²⁺ and Cu²⁺) restrict structural expansion and produce flexible dimeric macrocycles [(M₂<i>R</i>/<i>S</i>L₂)(PF₆)₄]. Moreover, the rigid [(M₄<i>R</i>/<i>S</i>L₄)(PF₆)₈] structure exhibits a higher asymmetry factor in the CD spectrum than [(M₂<i>R</i>/<i>S</i>L₂)(PF₆)₄] dimeric macrocycles. The findings of this work have established the pivotal role of metal ion in determining chiroptical activity, offering an effective strategy for developing high-performance chiral optical materials via precise coordination bond modulation.