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

Abstract

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.