Dual‐Mode Separation of C ₄ Hydrocarbons in Flexible Cu(ina) ₂ MOF

ABSTRACT

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 C ₄ hydrocarbon separation. At 298–308 K, phase C achieves an ultrahigh IAST selectivity of 15428.6 for n ‐butane/ i ‐butane ( n ‐C ₄ H ₁₀ / i ‐C ₄ H ₁₀ ), and efficiently separates i ‐C ₄ H ₁₀ from butene isomers ( n ‐butene/ i ‐butene, n ‐C ₄ H ₈ / i ‐C ₄ H ₈ ) and 1,3‐butadiene (C ₄ H ₆ ). The flexible framework also exhibits stimulus‐responsive behavior toward i ‐C ₄ H ₈ . Column breakthrough results demonstrate its excellent separation capability toward three typical C ₄ mixtures: i ‐C ₄ H ₁₀ / i ‐C ₄ H ₈ /C ₄ H ₆ , n ‐C ₄ H ₁₀ / i ‐C ₄ H ₁₀ and n ‐C ₄ H ₈ / i ‐C ₄ H ₈ . 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 C ₄ hydrocarbon purification.