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

A flexible tetradentate ligand, <b>L</b>,1,2,4,5-tetrakis((pyridin-4-ylthio)methyl)benzene, was designed to precisely construct topologically distinct handcuff-shaped molecules <b>1</b>,<b>2</b> and Double-Z cage <b>1</b> through coordination-driven self-assembly with building blocks (<b>B1</b>-<b>B3</b>). In particular, the size of the conjugated surfaces of <b>B1</b>-<b>B3</b> 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 <b>B1</b> and <b>B2</b>, while <b>Double-Z Cage 1</b> with a larger conjugated building block <b>B3</b>. Intriguingly, when BF₄^- is replaced with OTf^-, the stronger electron-donating and hydrogen bond-accepting capabilities of OTf^- induce a topological transformation from <b>Handcuff 2</b> to <b>Double-Z Cage 3</b>. Specifically, <b>Handcuff 1</b> and <b>Double-Z Cage 1</b> correspond to <b>Handcuff 3</b> and <b>Double-Z Cage 2</b>, respectively, demonstrating how anion identity influences the final topology for similar building blocks. Furthermore, a remarkable <i>in situ</i> topological transformation from <b>Handcuff 2</b> to <b>Double-Z Cage 3</b> was achieved under mild conditions with the addition of KOTf to <b>Handcuff 2</b>, as confirmed by real-time ¹H NMR monitoring. This work offers promising avenues for designing responsive molecular materials with tailored topologies.