Two Robust Isoreticular Metal-Organic Frameworks with Different Interpenetration Degrees Exhibiting Disparate...

Herein, two robust isoreticular metal-organic frameworks (MOFs), ([Bi(CPTTA)]·[Me₂NH₂]·2DMF) (JLU-MOF120, H₄CPTTA = 5'-(4-carboxyphenyl)-[1,1':3',1″-terphenyl]-3,4″,5-tricarboxylic acid, DMF = N, N- dimethylformamide) and ([In(CPTTA)]·[MeNH₃]·2.5H₂O·1.5NMF) (JLU-MOF121, NMF = N- methylformamide), with different interpenetration degrees were successfully constructed. According to the hard-soft acid-base (HSAB) theory, high-valent metal ions and carboxylate-based ligands were selected and formed twofold interpenetrated structures with saturated coordinated mononuclear second building units ([M(COO)₄], M = Bi, In). Owing to the features of the frameworks, JLU-MOF120 and JLU-MOF121 exhibited excellent stability, which could retain their integrity in water for at least 14 days and aqueous solutions with a pH range of 3-11 for at least 24 h. According to the structural regulation strategy, by changing the torsion angles of the ligand, the degrees of interpenetration for JLU-MOF120 and JLU-MOF121 were different, leading to various gate-opening pressures in CO₂ at 195 K. Furthermore, JLU-MOF120 exhibits the scarce potential of C₂H₂/CO₂ separation among Bi-MOF materials at 298 K under 101 kPa, JLU-MOF121 shows high CO₂/CH₄ selectivity under ambient conditions (11.7 for gas mixtures of 50 and 50% and 16.1 for gas mixtures of 5 and 95%). Moreover, owing to the flexibility of the structure, JLU-MOF121 possesses disparate breathing behaviors for C₂H₂ and C₂H₆ at 273 and 298 K, with the differences in uptakes among C₂ hydrocarbons resulting in the potentiality of C₂H₄ purification. Overall, such HSAB theory and the structural regulation strategy could provide a valid method for constructing stable and flexible structures for the application in gas separation.