Unveiling the Structure–Modulator Relationships in Thorium-Based Metal–Organic Framework Crystallization
Shujing Hou, Fusheng Liu, Haomiao Xie, Sylvia L. Hanna, Karam B. Idrees, Chenghui Zhang, Xingjie Wang, Yongwei Chen, Peng Li, Omar K. Farha
Abstract
Acid modulator has been the most widely employed ingredient for highly crystalline metal–organic framework (MOF) synthesis. However, the mechanistic understanding of thorium (Th)-based MOF crystallization remains a great challenge due to the intrinsic properties of fast olation and oxolation reactions of Th species in solution. Here, we constructed a series of Th-based MOFs by adding different modulators (formic acid, acetic acid, trifluoroacetic acid, and benzoic acid) to a synthetic solution along with tetratopic 1,3,5,7-adamantane tetracarboxylic acid (H 4 ATC), a three-dimensional (3D) ligand with a rigid aliphatic backbone. This work presents an in-depth study of the structure–modulator relationship between the H 4 ATC ligand and coordinating modulators in the Th-based MOF crystallization process. Crystal structures of these Th-based MOFs reveal that formic acid and acetic acid modulators can compete with the H 4 ATC ligand to form NU-52 and NU-54; these MOFs possess Th nodes linked by the corresponding modulator. Alternatively, usage of trifluoroacetic acid and benzoic acid modulators results in NU-53 and NU-55; these MOFs possess Th nodes coordinated by only the H 4 ATC ligand, regardless of the modulator amount. This work highlights that both the identity and amount of modulator play a crucial role in determining the resulting Th-based MOF structures when H 4 ATC is selected as the coordinated ligand.