Synergistic Regulation of Nitrogen Atoms and Metal Sites in In(III)/Fe(III)-MOFs: Study on the Adsorption and Separation Performance of C2H2/CO2

Abstract

This study demonstrates a systematic strategy for precisely modulating the secondary building units (SBUs) in indium-based metal–organic frameworks (MOFs). It is achieved by synergistically combining gradient regulation of nitrogen-atom content in ligands with heterometallic Fe3+ doping. We have successfully constructed a series of robust porous In (III)/Fe (III)-MOFs that exhibit distinct cluster structures, ranging from unique pentanuclear cluster [In5(μ3-O)2] to homogeneous/heterometallic trinuclear clusters. The research reveals that heterometallic doping primarily governs the evolution of cluster nuclearity through a geometric effect. Meanwhile, the electronic effect of ligand nitrogen atoms fine-tunes the coordination microenvironment and electron density of the metal centers. This multilevel control over the SBUs directly determines the final pore characteristics and gas separation performance. Gas adsorption and dynamic breakthrough experiments demonstrate that these MOFs materials enable effective capture and selective separation of C2H2 from C2H2/CO2 gas mixtures. This work establishes a clear structure–property relationship, spanning from ligand design and SBU control to macroscopic separation performance.