Structurally dynamic crystalline 1D coordination polymers enabled via the Weak-Link Approach

Supramolecular chemistry has the potential to be used to impart dynamic molecular elements into coordination polymers so that sophisticated, multifunctional materials can be prepared. Indeed, the Weak-Link Approach (WLA) to supramolecular chemistry is a coordination chemistry-based platform that can be used for the design of stimuli-responsive and switchable nanoscale architectures. Herein, we use the WLA to design and synthesize crystalline, WLA-based 1D coordination polymers. Specifically, the reaction of a closed, pyridine-functionalized WLA monomer complex with Cu(BF₄)₂·6H₂O in acetonitrile or N,N-dimethylformamide yields three isostructural 1D zig-zag chains. One of the polymers was studied via single-crystal X-ray diffraction (SCXRD), nuclear magnetic resonance (NMR) spectroscopy, and mass spectroscopy (MS), and its response to a chemical effector (halide ion, Cl⁻) was investigated. Importantly, our investigation of one of the model chains displays the characteristic structural switchability of the WLA complex from which it is comprised. Upon exposure to Cl⁻ anions, it disassembles into its molecular components, including the fully-opened congener of the initial WLA complex. Thus, one can control crystalline chain assembly via the structural state of the WLA monomer complex. Taken together, this work has demonstrated the construction of the first series of crystalline WLA-based extended solids and represents a promising method for the construction of allosteric, stimuli-responsive coordination polymers, including potentially higher-ordered structures like metal organic frameworks.