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

Two thorium-organic frameworks of [Th₆O₄(OH)₄(TFBPDC)₆(H₂O)₆] (Th-TFBPDC) and [Th₆O₄(OH)₄(TFBPDC)₄(HCOO)₄(H₂O)₆] (Th-TFBPDC-i) constructed from the 3,3',5,5'-tetrakis(fluoro)biphenyl-4,4'-dicarboxylate (TFBPDC^2-) 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 TFBPDC^2- 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.