Thiacalix[4]arene-Protected Titanium–Oxo Clusters: Influence of Ligand Conformation and Ti–S Coordination on the Visible-Light Photocatalytic Hydrogen Production

Abstract

p-tert-Butylthiacalix[4]arene (H4TC4A)-decorated tetranuclear (Ti4) and hexanuclear (Ti6) polyoxo–titanium clusters (PTCs) were synthesized in isopropyl alcohol by a low-temperature solvothermal method. The structures were determined by single-crystal X-ray diffraction, in which the ligands adopt 1,2-alternative and cone-shaped conformations, respectively. Both PTCs show UV–vis absorptions up to 600 nm with band gaps at 2.19 eV (Ti4) and 2.24 eV (Ti6), respectively. Visible-light photocatalytic H2 production for Ti4 was measured to be 73.56 μmol/(g h), which is almost 5 times of that of Ti6 (15.16 μmol/(g h)). Results of density functional theory (DFT) calculations suggested that the different Ti–S coordination modes originating from the conformational disparity of the ligands are primarily responsible for the observed different photocatalytic activities. Not only does this work provides a better understanding of the structure–property relationships in using titanium–oxo clusters for photocatalytic H2 production but it also offers a means of tuning the band gap of the catalysts by varying the conformations of the ligands.