Metal–Organic Frameworks: Semiconducting Frameworks

Abstract

Abstract The number of semiconductive networks grows; the synthetic strategy verges on major breakthroughs—but they are not yet fully recognized by the community. This chapter aims to help fill in this void. We follow certain historical threads in the development of coordination networks/metal–organic frameworks, and by so doing, identify synthetic methods that are poised to be broadly effective for achieving semiconductivity within porous framework materials. Sulfur‐functionalized building blocks (thiols and thioethers) dominate the collection of compounds, because of the generally important electronic properties of metal–sulfur compounds, and because of the broad methodological implications exemplified by these materials. The major strategies identified herein centered on tackling the often intractable metal–sulfur bond as the linker for network construction. In one approach, the sulfur (e.g., thiolate) group is abutted by electron‐withdrawing pyridinyl or carboxylic units, in order to temper the metal–sulfur interaction, and thus to promote the formation of well‐ordered, crystalline framework products. The carboxyl‐sulfur combination also points to the more generally applicable hard‐and‐soft approach for network syntheses. For example, a chemically hard metal ion such as Zr(IV) selectively bonds to the carboxylate moiety to build up the porous net, whereas the sulfur (thiol or thioether) groups stay free‐standing—and they can then take up various guest metal ions for installing the desired metal–sulfur interactions. Such a two‐step strategy smacks of the now popular practice of postsynthesis modification of metal–organic frameworks, which, in turn, harkens back to some seminal works on the less robust Ag(I)–nitrile networks around the turn of the century. In the third approach, thiol units are built onto a rigid and multiarm aromatic core (e.g., triphenylene), which is then directly reacted with metal ions to generate the semiconductive framework product. The crux here is to invoke the very rigid nature of the building block, and to enforce substantial porous feature in the solid product, although the crystallinity of the latter might be compromised due to the fast and irreversible metal–sulfur interactions.