Tartrate-stabilized titanium-oxo clusters containing sulfonate chromophore ligands: synthesis, crystal structures and photochemical properties

Titanium-oxo clusters (TOCs), as a new class of molecular functional materials, have become one of the key research areas due to their novel structures and fascinating properties. Herein, two new tartrate-stabilized TOCs with sulfonate chromophore ligands, Ti-4(C4H2O6)(AS)(2) ((OPr)-Pr-i)(10) (1) and Ti-4(C4H2O6)(ATS)(2)((OPr)-Pr-i)(10)(2) (C4H2O6 = tartrate, AS = aniline-2-sulfonate, and ATS = 4-aminotoluene-3-sulfonate), have been synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy, UV-vis diffuse reflection spectroscopy, thermogravimetric analysis, powder X-ray diffraction analysis, and single crystal X-ray diffraction. Their structural analyses indicate that the crystals are a class of small TOCs containing only four titanium atoms in the asymmetric unit, which form a centrosymmetric planar square {Ti-4} core chelated by a bridging hexadentate tartrate ligand in trans orientation. Both TOCs show UV-vis absorption up to 600 nm with band gaps of 3.16 eV (for 1) and 2.95 eV (for 2), respectively. The photocurrent response and the photocatalytic activity for degradation of organic dye methylene blue (MB) have also been examined. Furthermore, the charge transfer from the sulfonate chromophore ligand to the {Ti-4} core (LCCT) was evaluated using density functional theory calculations.