π‐conjugated chromophore functionalized high‐nuclearity titanium‐oxo clusters containing structural unit of anatase for photocatalytic selective oxidation of sulfides

Abstract

Abstract N‐doping has significant influence in manipulating the properties of TiO 2 , and this has stimulated the development of N‐donor‐functionalized titanium‐oxo clusters (TOCs) as molecular models to study the structure–property relationship. However, the structural type and photoresponsive application are still limited for such TOCs, especially regarding the high‐nuclearity TOCs that contain structure unit of TiO 2 for photocatalysis. Herein, we showed the synthesis of a series of high‐nuclearity TOCs 1–3 compounds using π‐conjugated 1,10‐phenanthroline (phen) as chromophore and N‐donor functional ligand. Compound 1 features cocrystal structure composed of one [Ti 26 ] 2+ and half [Ti 22 ] 2+ , which renders it as the first cocrystallized TOC containing two positively charged species and phen‐functionalized TOC showing the highest nuclearity up to 37 Ti centers. By adjusting the synthetic conditions, the individual {Ti 22 } and {Ti 26 } clusters can also be isolated as Compounds 2 and 3, respectively. The core structure of {Ti 22 } is mainly constructed from four lacunary {Ti 4 } derived from pentagonal {Ti(Ti) 5 } unit, while {Ti 26 } is built from four complete {Ti(Ti) 5 } unit. Notably, a {Ti 8 O 14 } structure unit of anatase TiO 2 can be identified in {Ti 26 }. Based on the unique structural features and proper photophysical and photochemical properties of Compounds 1–3, they are applied for photocatalytic sulfoxidation. Owing to the presence of anatase structure unit in {Ti 26 } and the synergistic effect from {Ti 22 } and {Ti 26 }, the catalytic performance presents in the order of Compound 1 > Compound 3 > Compound 2. This work provides excellent models to understand the structure–property relationship from the perspective of cocrystallization and Ti–O binding model and will further promote the application of TOCs as functional catalysts for organic transformation.