Ligand-Symmetry-Driven Metal-Cluster Rotation for Accessing Compressed Pore Regimes in Metal-Organic Frameworks

Isoreticular chemistry conventionally tunes pore dimensions by varying linker length or manipulating substituents. While widely used, this strategy is constrained by the intrinsic chemistry of molecular building units, rendering certain size regimes and pore geometries inaccessible. Here, we establish coordination symmetry as an independent and powerful design variable for unit-cell compression in pore-partitioned acs (pacs) metal-organic frameworks. Replacement of D_3h-symmetric tris(4-pyridyl) ligands with their C_3h-symmetric tris(3-pyridyl) positional isomers induces controlled rotation of metal clusters without altering ligand size or framework topology. Curvature-encoded dicarboxylate linkers define a finite metal-cluster rotation window, within which donor-position symmetry selects distinct rotational states, producing systematic contraction along the hexagonal a/b directions and up to ∼15% reduction in unit-cell volume. Across multiple metal trimers and ligand combinations, this symmetry-controlled compression enhances framework stability and dramatically improves gas-separation performance. Importantly, the strategy enables simultaneous increases in C₂H₂ uptake and C₂H₂/CO₂ or C₂H₂/C₂H₄ selectivity, overcoming the commonly observed trade-off between adsorption capacity and selectivity in porous material design. Ni₃-24fdc-3tpt achieves record C₂H₂/CO₂ and C₂H₂/C₂H₄ selectivities within the pacs family (42.35 and 25.14, respectively), together with high separation potentials and robust breakthrough performance. These results demonstrate that ligand-symmetry-driven metal-cluster rotation provides a general and predictive route to access compressed pore regimes beyond conventional linker-length modulation and expands the conceptual framework of isoreticular chemistry.