Structure Transformation of a Luminescent Pillared-Layer Metal–Organic Framework Caused by Point Defects Accumulation

Pillared-layer metal–organic frameworks (MOFs) are often encountered to “collapse” upon external stimuli due to weak interactions between the layers and the pillars. However, the detailed local structural change, especially the accumulation of defects due to intricately disordered bond dissociations, is not clear due to the complicated and dynamic nature of the collapse. We report a luminescent pillared-layer MOF structure, FDM-22, using zinc dicarboxylates as layers and dipyridyl ligands as pillars, in which three different transformed structures were captured along the increasing number of coordination bond dissociations between zinc metals and pyridine linkers. The transformation is triggered by these local point defect formations in the MOF, which further contribute to the modulation of its luminescence property, as well as prominent change in the morphology and pore distribution of the MOF. Evidenced by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), each of the pillar ligands has only one pyridyl group coordinated to a Zn­(II) ion eventually, with the other uncoordinated pyridyl group pointing to the pore. With ∼10% of the coordination bonds breaking within the framework, FDM-22 provides a high concentration of active metal sites in the framework.