Amino-Polyalcohol-Solvothermal Synthesis of Titanium-Oxo Clusters: From Ti₆ to Ti₁₉ with Structural Diversity

As is known, amino-polyalcohol ligands are usually used as sacrificial agents in photocatalytic reactions. And polyoxo-titanium clusters (PTCs) are molecular modes of titanium dioxide, one of the most important photocatalysts. In order to help understand the intrinsic coordination feature of amino-polyalcohol toward titanium-oxo species, we carried out the research of constructing PTCs with amino-polyalcohol ligands. In view of the low melting point of amino-polyalcohol, they have been directly applied as reaction mediums. Under this new synthetic method, a series of PTCs have been successfully obtained, namely, Ti₆(μ₂-O)₂(OCH₂CH₂O)₂(O ⁱPr)₄(dea)₆·HO ⁱPr (deaH₂ = diethanolamine, PTC-171), Ti₉(μ₂-O)₂(μ₃-O)₄(tea)₂(O ⁱPr)₈(dea)₅(teaH₃ = triethanolamine, PTC-172), Ti₁₁(μ₃-O)₁₀(μ₄-O)(O ⁱPr)₁₄(dea)₄ (PTC-173), Ti₁₉(μ₂-O)₆(μ₃-O)₁₂(dea)₁₈Cl₄ (PTC-174), and Ti₁₉(μ₂-O)₆(μ₃-O)₁₂(dea)₁₈(NO₃)₄·(H₂O)₆ (PTC-175). Their structures are determined by single-crystal X-ray diffraction analysis. It is worth noting that PTC-174 and PTC-175 are not only the first Ti₁₉ examples of crystalline PTCs, but also currently the largest PTCs compounds in the amino-polyalcohol system. Moreover, the solid-state UV-vis spectra of these PTCs were recorded. And their applications in photocurrent responses were also investigated. This work provides an interesting method for the preparation of amino-polyalcohol base PTCs and would also benefit the mechanism interpretation of the photocatalytic processes of titanium oxide materials.