Exposed Equatorial Positions of Metal Centers via Sequential Ligand Elimination and Installation in MOFs

Metal–organic frameworks (MOFs) provide highly designable platforms to construct complex coordination architectures for targeted applications. Herein, we demonstrate that trans-coordinated metal centers with exposed equatorial positions can be placed in a MOF matrix. A Zr-based MOF, namely, PCN-160, was initially synthesized as a scaffold structure. Postsynthetic linker labilization was subsequently implemented to partially remove the original dicarboxylate linkers and incorporate pyridinecarboxylates. A pair of neighboring pyridyl groups was arranged at proper proximity within the framework to form trans-binding sites that accommodate different metal cations including Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Pd2+. Furthermore, the trans-coordinated Ni2+ sites in porous frameworks can be readily accessed by substrates along the equatorial plane, facilitating the catalysis as manifested by the superior activity in ethylene dimerization over that observed for a cis-chelated catalyst