On the Importance of Squaramide and Squarate Derivatives as Metal–Organic Framework Building Blocks

In this review article the synthesis and solid state structure of squaramide/squarate based metal–organic frameworks (MOFs) are analyzed and discussed. In detail, a thorough search in the literature revealed the successful utilization of these two organic molecules as MOF building blocks capable of catalyzing (i) water splitting reactions, (ii) electrocatalytic oxygen evolution reactions, and (iii) Michael addition reactions. Additionally, some of the highlighted examples also utilized these two molecular synthons to compose MOFs exhibiting gas adsorbent properties, concretely for capturing propadiene and propylene. In each of the selected examples a theoretical study of the noncovalent interactions (NCIs) established between the squaramide/squarate-based MOF and the guest molecules trapped inside was carried out, providing additional information regarding the strength of the MOF–guest interactions, which certainly influence the catalytic/adsorbent capabilities of these materials. We believe that the examples collected herein will be useful for those scientists working in the fields of supramolecular chemistry, crystal engineering, catalysis, and materials science by providing a retrospective guide on the role of squaramide and squarate in the formation of MOFs.