Coordination-bond-directed synthesis of hydrogen-bonded organic frameworks from metal-organic frameworks as templates

Controlled synthesis of hydrogen-bonded organic frameworks (HOFs) remains challenging, because the self-assembly of ligands is not only directed by weak hydrogen bonds, but also affected by other competing van der Waals forces. Herein, we demonstrate the coordination-bond-directed synthesis of HOFs using a preformed metal-organic framework (MOF) as the template. A MOF (Cu^I-TTFTB) based on two-coordinated Cu^I centers and tetrathiafulvalene-tetrabenzoate (TTFTB) ligands was initially synthesized. Cu^I-TTFTB was subsequently oxidized to the intermediate (Cu^II-TTFTB) and hydrated to the HOF product (TTFTB-HOF). Single-crystal-to-single-crystal (SC-SC) transformation was realized throughout the MOF-to-HOF transformation so that the evolution of structures was directly observed by single-crystal X-ray diffraction. The oxidation and hydration of the Cu^I center are critical to breaking the Cu-carboxylate bonds, while the synergic corbelled S⋯S and π⋯π interactions in the framework ensured stability of materials during post-synthetic modification. This work not only provided a strategy to guide the design and discovery of new HOFs, but also linked the research of MOFs and HOFs.