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 Mg 2+, Co 2+, In 3+, and V 3+ 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 C 2 H 2 /CO 2 and C 2 H 6 /C 2 H 4 separation behavior. Notably, neutral CoV-dtc-tpt exhibits a high C 2 H 6 uptake of 164.8 cm 3 g –1 and excellent inverse-selective C 2 H 6 /C 2 H 4 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.