Syntheses, structures and ligand binding modes of titanium-oxide complexes of 2-picolinate

Six titanium-oxide clusters (TOCs) comprised of 6-19 Ti atoms all of which are of nanometer size were synthesized with the functionalization of 2-picolinate (PA). Their structures were determined by single-crystal X-ray diffraction and a few complementary spectroscopic techniques. The binding modes of PA on the surface of the TOCs were analyzed and found to be limited to only one binding mode, that is, PA acts as a bidentate ligand through both pyridyl-N and the carboxylate-O. UV-vis diffuse reflection spectra and electron paramagnetic resonance spectra indicate the ligand-to-metal charge transfer (LMCT) through the N-Ti bond. However, the LMCT band in the visible light region (400-600 nm) is very weak. Hence, picolinates do not bring about intense visible light absorption to TOCs. The binding mode of PA on the TOC surfaces and the LMCT revealed herein may be inspiring for studies on classical picolinate/TiO2-based dye-sensitized solar cells.