Tunable three-component metal-organic frameworks consisting of spanning bis(tridentate) linkers with six N/O-donor atoms: design, synthesis, properties and applications

Abstract

In the history of metal-organic frameworks (MOFs) comprised of flexible counterparts, it is a challenge to understand and predict the pathways involved in their synthetic process. Compared to the unlimited number of conventional two-component systems containing multi-topic carboxylates, the synthesis of three-component systems is more complex in nature. Among the flexible linkers, examples with two, four, and six N-donor atoms have been systematically studied for the effect of denticity and flexibility on the structural features and dimensionalities of the architectures. There is a plethora of examples of linkers with two N-donor atoms reported by many researchers including us, whereas the linkers with six N/O-donor atoms have been utilized exclusively by our group. In this perspective, we will shed light on the self-assembly process of MOFs mostly at room temperature from a three-component reaction involving (a) flexible spanning bis(tridentate) linkers with six N/O-donor atoms, (b) various linear and bent dicarboxylates, and (c) divalent metal centers. The underlying factors - flexibility and angularity of dual linkers - that govern the formation of 2D and 3D MOFs will be emphasized. This strategy is undoubtedly a paradigm shift, which has opened up a path of designing 3D MOFs comprising flexible counterparts. Exploiting the inherent properties of selected MOFs, their application in (a) sensing of environmental pollutants, (b) heterogeneous catalysis of several important organic transformations, (c) multi-media iodine capture, and (d) CO2 capture and conversion are highlighted. Mechanistic considerations for each process are elaborated.