Dual-Mode Separation of C₄ Hydrocarbons in Flexible Cu(ina)₂ MOF

We present two synthetic routes to prepare thermodynamically stable copper-isonicotinate (Cu(ina)₂) MOF, including direct in situ synthesis and thermal-induced irreversible phase transformation from metastable phase P. The P→C transition proves that phase C is thermodynamically favorable. Both methods produce phase C with identical structure and show exceptional performance in C₄ hydrocarbon separation. At 298-308 K, phase C achieves an ultrahigh IAST selectivity of 15428.6 for n-butane/i-butane (n-C₄H₁₀/i-C₄H₁₀), and efficiently separates i-C₄H₁₀ from butene isomers (n-butene/i-butene, n-C₄H₈ / i-C₄H₈) and 1,3-butadiene (C₄H₆). The flexible framework also exhibits stimulus-responsive behavior toward i-C₄H₈. Column breakthrough results demonstrate its excellent separation capability toward three typical C₄ mixtures: i-C₄H₁₀/i-C₄H₈/C₄H₆, n-C₄H₁₀/i-C₄H₁₀ and n-C₄H₈/i-C₄H₈. As a flexible framework, Cu(ina)₂ realizes separation via a dual-mode mechanism of size exclusion and thermodynamic host-guest interactions. DFT and MD simulations reveal that pyridine ligand rotation triggers structural deformation and energy dissipation upon adsorption. The synergistic effect guarantees outstanding separation performance, and phase C is a promising benchmark adsorbent for C₄ hydrocarbon purification.