Structures and Electronic Properties of Titanium Oxo Clusters with Tartrate Ligand: A Density Functional Theory Study

Titanium oxo clusters are considered a model for nanotitanium dioxide and have gradually become a new field of functional materials in solar cells. In this work, the precise structural information of two types of tartrate-based titanium-oxo clusters was investigated by quantum chemical approaches. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations provided the precise structural parameters of Ti4(C4H2O6)(AS)2(OiPr)10 and Ti4(C4H2O6)(ATS)2(OiPr)10. Our work provided reliable results in agreement with the experimental results. In both molecules, the Ti-O bonds were mainly divided into three categories: the bonds in the first category were the coordination bonds between the central skeleton Ti atom and the tartaric acid group, whose bond lengths were 2.000 – 2.080 Å; the bonds in the second category were the coordination bond formed by the Ti atom and the oxygen on the AS ligand sulphonic acid group, whose bond lengths were 2.148 – 2.310 Å; the bonds in the third category were the Ti-O bonds with shorter bond lengths, which were the coordination bond formed by the Ti atom and the oxygen on the isopropylalkoxy group with their bond lengths in the value range from 1.777 Å to 1.795 Å. These kinds of Ti-O bonds also can be found in other Ti4 titanium-oxo clusters. Molecular orbitals showed that electron transfer from the AS/ATS ligand to the {Ti4} central skeleton was induced by sunlight with maximum UV-Vis absorption of 605/629 nm. Our calculation results provide strong guidance for the discovery of new efficient titanium oxo in solar cells.