Thermally Induced Topological Isomers of Metal–Organic Frameworks for Enhanced C₂H₂ Separation from CO₂ and C₂H₄

Although isomerism is a fundamental and well-explored phenomenon in organic chemistry, its occurrence in metal-organic frameworks (MOFs) remains rare. Here, we present a novel class of MOF topological isomers that share identical molecular formulas and secondary building units (SBUs), yet exhibit distinct network architectures. These isomers, differentiated by their <i>PtS</i> and <i>NbO</i> topologies, arise from variations in ligand conformation due to steric constraints. The isomerization is thermally induced and driven by ligand rotation during solvothermal synthesis. Notably, these topological differences profoundly influence their pore geometries and dimensions, ultimately governing their gas adsorption properties. Comparative studies demonstrate that the <i>PtS</i>-type network exhibits superior C₂H₂ uptake and enhanced C₂H₂ selectivity over C₂H₄ and CO₂ compared to the <i>NbO</i>-type network. Theoretical studies reveal the crucial role of pore size and geometry in achieving high C₂H₂ selectivity. This work not only introduces a new strategy for constructing MOF isomers but also advances structural diversity in porous materials, opening avenues for their tailored applications.