Conductive MOFs based on Thiol-functionalized Linkers: Challenges, Opportunities, and Recent Advances

In old days, application of MOFs in the field of electrochemical catalysis and electronic device fabrication was not common because MOFs generally exhibited low electrical conductivity. However, within these decades, various approaches have been developed for assembling electrically conductive MOFs. Among these approaches, using thiol-functionalized linkers to assemble thiol-decorated MOFs (thiol-MOFs) represents a novel and effective way since sulfur groups facilitate interlayer charge delocalization and hence electrical conductivity in MOFs. Generally speaking, thiol-MOFs can be generally divided into two types: (1) structure constructed from soft metal ions and dithiolene linker molecules with planarity, π-conjugation and redox activity; (2) framework assembled from hard metal ions and linker molecules with both carboxyl and thiol groups, where thiol (–SH) groups exist as free-standing functional group or coordinating group in robust porous coordination networks. Gratifyingly, some of the reported MOFs bearing thiol-functionalized ligands have shown outstanding electrical conductivity which highlight the thiol-MOFs as future materials in the field of conductive/semiconductive MOFs. Unfortunately, the demanding synthetic conditions of thiol-functionalized linkers (such as the foul odor of sulfur reagents, harsh synthetic conditions), poor crystallinity of thiol-MOFs and difficult characterization of unstable thiol-MOFs discourage extensive exploration of this linker family and its MOF derivatives. Despite the difficulty, exploration of these thiol-MOFs still made progress in recent years. To make sulfur-functionalized linkers and MOFs more popular, design strategies and synthetic protocols of thiol-functionalized linkers, growing strategies of thiol-MOFs and recent advances of thiol-MOFs in different application studies are discussed in this review. At last, a perspective is given to cover the future prospect of thiol-functionalized linkers and thiol-MOFs so as to provide insights for researchers interested in investigating thiol-MOFs.