Electron-deficient defect sites in polyoxometalate-based metal-organic frameworks induced by atom substitution-modulated host-guest interaction.

The strategic introduction of defects in polyoxometalate-based metal-organic frameworks (POM@MOFs) enables synergistic catalytic effects between POMs and defect sites, achieving catalytic functions unattainable by either component alone. However, the complexity of the POM@MOFs synthetic system makes the controlled construction of defects more challenging than in conventional MOFs. Herein, we develop an atomic substitution-modulated host-guest interaction strategy for controlled synthesis of electron-deficient defect sites in POM@MOFs with tunable missing-linker content. Specifically, the gradual substitution of Mo atoms with V atoms in HPMoO (PMo) enhances the nucleophilicity of surface oxygen species, thereby strengthening the interaction between POMs and Zr-oxo clusters in UiO-67. This enhanced interaction induces varying degrees of ligand loss through coordination competition of POMs with organic ligands during the self-assembly of POM@UiO-67. Meanwhile, POMs acting as electron sponges withdraw electrons from UiO-67, resulting in lower electron density at defect sites compared to traditional defective UiO-67. The induced defect sites exhibit superior catalytic performance in the transfer hydrogenation of cinnamaldehyde, due to a significantly reduced hydrogen transfer energy barrier. This work provides a new perspective for designing crystalline porous catalysts with synergistic effects based on the modulation of host-guest interaction.