Supramolecular chirality transformation driven by monodentate ligand binding to a coordinatively unsaturated self-assembly based on C(3)-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 C(3)-symmetric chiral ligands. The C(3)-symmetric chiral ligands (Im(R)(3)Bz and Im(S)(3)Bz) contain three chiral imidazole side arms (Im(R) and Im(S)) at the 1,3,5-positions of a central benzene ring. Upon coordination to zinc ions (Zn(2+)), which have a tetrahedral coordination preference, the C(3)-symmetric chiral ligands assemble, in a stepwise manner, into a propeller-shaped assembly with a general formula (Im(()(R)(or)(S)())(3)Bz)(4)(Zn(2+))(3). In this structure each Zn(2+) ion coordinates to the three individual imidazole side arms. The resulting assembly is formally coordinatively unsaturated (coordination number, n = 3) and capable of accepting monodentate co-ligands (imidazole: ImH(2)) to afford a coordinatively saturated assembly [(ImH(2))(3)(Im(R)(3)Bz)(4)(Zn(2+))(3)]. The preformed propeller-shaped chirality is preserved during this transformation. However, an excess of the monodentate co-ligand (ImH(2)/Zn(2+) molar ratio of ∼1.7) alters the propeller-shaped assembly into a stacked dimer assembly [(ImH(2))(m)(Im(R)(3)Bz)(2)(Zn(2+))(3)] (m = 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.