Compositional Tunability and Framework-Charge Modulation in Pore-Space-Partitioned Metal-Organic Frameworks

Trimer-based metal clusters are among the most compositionally versatile secondary building units in metal-organic frameworks (MOFs), but systematic control of heterometallic composition and framework charge within a structurally invariant platform remains challenging. Here, pore-space-partitioned acs (pacs) frameworks are employed as a model system to investigate compositional tunability at both the cluster and framework levels. Using 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylate (dtc), a family of homo- and heterometallic pacs-MOFs based on Mg²⁺, Co²⁺, In³⁺, and V³⁺ trimers was synthesized. In the charge-complementary Mg/In system, variation of metal precursors and solvents enables broad tuning of the Mg/In ratio, while the large atomic-number contrast permits reliable occupancy refinement by single-crystal X-ray diffraction. The trimeric platform also supports an isostructural Co-, Co/V-, and V-based series in which framework charge changes from anionic to neutral and cationic without altering topology. Gas adsorption studies reveal charge-dependent C₂H₂/CO₂ and C₂H₆/C₂H₄ separation behavior. Notably, neutral CoV-dtc-tpt exhibits a high C₂H₆ uptake of 164.8 cm³ g^-1 and excellent inverse-selective C₂H₆/C₂H₄ separation, rivaling benchmark pacs materials. These results establish pacs-MOFs as a versatile platform for studying heterometallic assembly, framework-charge modulation, and structure-composition-property relationships.