Structural Evolution from Noninterpenetrated to Interpenetrated Thorium-Organic Frameworks Exhibiting High Propyne Storage.

Two thorium-organic frameworks of [Th6O4(OH)4(TFBPDC)6(H2O)6]n (Th-TFBPDC) and [Th6O4(OH)4(TFBPDC)4(HCOO)4(H2O)6]n (Th-TFBPDC-i) constructed from the 3,3',5,5'-tetrakis(fluoro)biphenyl-4,4'-dicarboxylate (TFBPDC2-) ligand were obtained in a reaction. At an early stage of the reaction, the formation of the three-dimensional (3D) framework of Th-TFBPDC was discovered. At a later stage of the reaction, the complete product of Th-TFBPDC-i was obtained. The structural evolution from a noninterpenetrated network of Th-TFBPDC to a 2-fold interpenetrated network of Th-TFBPDC-i is a dissolution-recrystallization process and rationalized as the four equatorial TFBPDC2- ligands in an octahedral [Th6O4(OH)4(TFBPDC)12] unit were displaced by four formate ligands to form a [Th6O4(OH)4(TFBPDC)8(HCOO)4] unit via a ligand substitution reaction. The large pore volume as well as the strong interactions between the host framework and guest propyne (C3H4) molecules demonstrated by computational results endow the highly water-stable Th-TFBPDC with the best-performing C3H4 storage under ambient conditions. This work presents a rare example of structural evolution from a 3D noninterpenetrated network to a 2-fold 3D interpenetrated network and a highly promising metal-organic framework (MOF) for C3H4 storage with a C3H4 uptake of 8.16 mmol g-1 at 298 K.