Supramolecular chirality transformation driven by monodentate ligand binding to a coordinatively unsaturated self-assembly based on -symmetric ligands.

Monodentate ligand binding is facilitated by supramolecular chirality transformations from propeller-shaped chirality into single-twist chirality by altering the self-assembly of -symmetric chiral ligands. The -symmetric chiral ligands ( and ) contain three chiral imidazole side arms (Im  and Im ) at the 1,3,5-positions of a central benzene ring. Upon coordination to zinc ions (Zn), which have a tetrahedral coordination preference, the -symmetric chiral ligands assemble, in a stepwise manner, into a propeller-shaped assembly with a general formula ()(Zn). In this structure each Zn ion coordinates to the three individual imidazole side arms. The resulting assembly is formally coordinatively unsaturated (coordination number, = 3) and capable of accepting monodentate co-ligands (imidazole: ImH) to afford a coordinatively saturated assembly [(ImH)()(Zn)]. The preformed propeller-shaped chirality is preserved during this transformation. However, an excess of the monodentate co-ligand (ImH/Zn molar ratio of ∼1.7) alters the propeller-shaped assembly into a stacked dimer assembly [(ImH) ()(Zn)] ( = 4-6) with single-twist chirality. This switch alters the degree of enhancement and the circular dichroism (CD) pattern, suggesting a structural transition into a chiral object with a different shape. This architectural chirality transformation presents a new approach to forming dynamic coordination-assemblies, which have transformable geometric chiral structures.