Assembly of 3D Coordination Polymers from 2D Sheets by [2+2] Cycloaddition Reaction

Abstract

The synthesis of three 2D interdigitated Zn(II) coordination polymers (CPs), by using three monotopic ligands containing C=C bonds, is reported. Among these, two CPs with 4spy (4-styryl pyridine) and 2F-4spy (a 2'-fluoro derivative of 4spy) ligands showed quantitative formation of cyclobutane rings, thus demonstrating a unique synthetic procedure to synthesize metal-organic frameworks (MOFs) by using this photochemical reaction. Interestingly, these compounds can also be synthesized by mechanochemical grinding procedures by using Zn(OAc)2. In contrast, Zn(NO3)2 did not yield the required product, unlike in the solution route. In addition, compounds with 4vpy (4-vinylpyridine), 4spy and 2F-4spy ligands created different units in the CPs; 4vpy and 2F-4spy furnished paddle wheel units, whereas 4spy yielded tetrahedral Zn(II) repeating units. Furthermore, the change in coordination geometry manifests in the photoluminescence properties, attributed to the difference in charge-transfer and ligand-centered fluorescent phenomenon.