Titanium Sulfonate-Based Metal-Organic Frameworks

Titanium-based metal-organic frameworks (Ti-MOFs) are one of the most active fields of MOFs due to their intriguing catalytic properties; however, the fast reaction between the widely used carboxylate-based ligand (hard base) and Ti4+ ion (hard acid) makes the syntheses of Ti-MOFs extremely challenging. In this work, we propose a new strategy by adopting sulfonic acid (soft base) as organic ligands to synthesize Ti-MOFs based on hard and soft acid and base (HSAB) theory. As an example of this strategy, seven titanium sulfonate metal-organic frameworks have been synthesized from 1,5-naphthalenedisulfonic acid (H2nds) and titanium isopropoxide and their structures are determined by single-crystal X-ray diffraction. These compounds exhibit permanent porosity, solvent stability, and light adsorption ability with a narrow band gap (2.67 eV). This work demonstrates a powerful method for the single-crystal syntheses of new Ti-MOFs, which will greatly promote the development of Ti-MOFs.