Unveiling the Structure-Modulator Relationships in Thorium-Based Metal-Organic Framework Crystallization

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Acid modulators are key for synthesizing highly crystalline metal-organic frameworks (MOFs).
• Understanding thorium (Th)-based MOF crystallization is challenging due to rapid Th species reactions.
• Thorium's unique properties necessitate specific strategies for controlled MOF synthesis.

Purpose of the Study:

• To investigate the structure-modulator relationship in thorium-based MOF synthesis.
• To explore how different carboxylic acid modulators influence MOF structures with a specific ligand.
• To elucidate the role of modulator identity and concentration in directing thorium MOF crystallization.

Main Methods:

• Synthesis of thorium-based MOFs using tetratopic 1,3,5,7-adamantane tetracarboxylic acid (H4ATC) ligand.
• Systematic variation of acid modulators (formic, acetic, trifluoroacetic, benzoic acid).
• Single-crystal X-ray diffraction analysis to determine the resulting MOF structures.

Main Results:

• Formic acid and acetic acid competed with H4ATC, forming MOFs (NU-52, NU-54) with Th nodes linked by the modulator.
• Trifluoroacetic acid and benzoic acid resulted in MOFs (NU-53, NU-55) where Th nodes were solely coordinated by H4ATC.
• The choice of modulator significantly altered the coordination environment around the thorium nodes.

Conclusions:

• The identity and amount of modulator critically determine the final structure of thorium-based MOFs.
• Modulators can either incorporate into the MOF structure or direct the coordination of the primary ligand.
• This study provides insights into controlling MOF topology through modulator selection in thorium chemistry.