Metal-dependent adsorption and photothermal-assisted catalysis in heterometallic metal–organic frameworks

Abstract

The modular nature of metal–organic frameworks (MOFs) enables structural and functional tuning through controlled combinations of organic linkers and metal ions. Here, we report an isostructural MOF series, M-DGIST-20, constructed from trinuclear TiM₂(μ₃-O)(COO)₆ (M²⁺ = Ni²⁺, Co²⁺, and Mn²⁺) clusters and a naphthalenediimide-based ligand. The frameworks feature high porosity (≈85% void volume) and serve as a platform to examine composition–function relationships. Iodine adsorption experiments reveal metal-dependent kinetics, with Ni-DGIST-20 showing the fastest uptake due to stronger M–I₂ interactions and higher structural robustness. Post-synthetic coordination of imidazole at open metal sites further increases the adsorption rate and capacity. In addition, efficient photothermal conversion and accessible metal sites in M-DGIST-20 allow localized heating and Lewis acidic catalysis, accelerating the Knoevenagel condensation and subsequent Michael addition-intramolecular cyclization. This study demonstrates how compositional and post-synthetic tuning can modulate adsorption and catalytic activity of MOFs.