Anion- and Conjugated Building Block-Driven Construction of Handcuffs and Cages, Featuring In Situ Topological Transformation from Handcuff to Double-Z Cage

A flexible tetradentate ligand, L,1,2,4,5-tetrakis((pyridin-4-ylthio)methyl)benzene, was designed to precisely construct topologically distinct handcuff-shaped molecules 1,2 and Double-Z cage 1 through coordination-driven self-assembly with building blocks (B1-B3). In particular, the size of the conjugated surfaces of B1-B3 and hydrogen bond-accepting properties of anions play critical roles in influencing the resulting topology, as supported by single-crystal X-ray diffraction (SCXRD), electrostatic potential (ESP), and independent gradient model (IGM) calculations. BF₄⁻ anions favored the formation of handcuff-shaped structures with smaller conjugated building blocks B1 and B2, while Double-Z Cage 1 with a larger conjugated building block B3. Intriguingly, when BF₄⁻ is replaced with OTf⁻, the stronger electron-donating and hydrogen bond-accepting capabilities of OTf⁻ induce a topological transformation from Handcuff 2 to Double-Z Cage 3. Specifically, Handcuff 1 and Double-Z Cage 1 correspond to Handcuff 3 and Double-Z Cage 2, respectively, demonstrating how anion identity influences the final topology for similar building blocks. Furthermore, a remarkable in situ topological transformation from Handcuff 2 to Double-Z Cage 3 was achieved under mild conditions with the addition of KOTf to Handcuff 2, as confirmed by real-time ¹H NMR monitoring. This work offers promising avenues for designing responsive molecular materials with tailored topologies.