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

Abstract

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.

Solvent‐Driven Reversible Phase Transition of a Pillared Metal–Organic Framework

“…Compared to the as‐synthesized YNU‐1 sample, powder X‐ray diffraction patterns showed that the sharp diffraction peaks diminished after transforming into YNU‐1 nanobelts, thereby revealing that the partly crystal structure changed after the water treatment (Figure A). This phenomenon was similar to the previous report on MOFs with phase transformation, in which the XRD pattern also completely changed in comparison to that of the original MOF . Unfortunately, owing to the low solubility of QBA in water, it was difficult to obtain a single crystal of YNU‐1 nanobelts.…”

“…Specifically,t he peaks at 1137.531,1 131.67,a nd 1134.62 eV correspond to the 6, 8, and 9-coordinated Eu, respectively ( Figure S10C). [38] The percentages of 8-coordinated Eu (from 5.79 to 29.98 %) clearly increased after water treatment, thusi ndicating that the coordination bonds of Eu cations with QBA ligandsw ere partly replaced by water molecules. The deconvolution of Or egionsr evealed the presence of two distinct Op eaks for both samples (Figure S10D).…”

“…Deconvolution of the Eu 3d 5/2 regions revealed the presence of three distinct Eu 3d 5/2 peaks. Specifically, the peaks at 1137.531, 1131.67, and 1134.62 eV correspond to the 6, 8, and 9‐coordinated Eu, respectively (Figure S10C) . The percentages of 8‐coordinated Eu (from 5.79 to 29.98 %) clearly increased after water treatment, thus indicating that the coordination bonds of Eu cations with QBA ligands were partly replaced by water molecules.…”

“…This phenomenon was similart o the previousr eport on MOFs with phase transformation, in which the XRD pattern also completely changed in comparison to that of the original MOF. [38,39] Unfortunately,o wing to the low solubility of QBA in water,i tw as difficult to obtainasingle crystal of YNU-1 nanobelts. To prove our assumption, we simulated the XRD of YNU-1 based on single-crystal data.…”

Enhancing Multicomponent Metal–Organic Frameworks for Low Pressure Liquid Organic Hydrogen Carrier Separations

“…Multicomponent MOFs have emerging applications in catalysis, luminescence and gas storage . In order to form multicomponent MOFs judicious selection of the linkers is essential (Figure , Scheme S1) .…”