A chelating coordination modulation method for the synthesis of Ti-MOF single crystals

Abstract

Even though titanium-based metal–organic frameworks (Ti-MOFs) are promising as efficient photocatalysts, the high reactivity of titanium ions makes the synthesis and structure determination of new Ti-MOFs quite challenging. In this study, we propose a chelating coordination modulation (CCM) method for the synthesis of Ti-MOF single crystals by using molecules with chelating coordination groups as the modulator. Thanks to this method, three Ti-MOFs (FIR-117–119) have been obtained and their structures were determined by single crystal X-ray diffraction (SCXRD), validating the universality of this approach. By capturing the intermediate and determining its single crystal structure, the role of the modulator in the growth of Ti-MOF single crystals is clarified: the use of a chelating coordination molecule as the modulator and a competitive ligand slows down the reaction rate by forming Ti–modulator key intermediates, which balance the formation of Ti-MOFs and growth of single crystals. Furthermore, FIR-119 exhibits excellent photocatalytic performance under visible light due to its good light absorption ability with a narrow bandgap. These results highlight the potential of the chelating coordination modulation method in the synthesis of new photoactive Ti-MOFs and their single crystals.