Synthesis, Structure, and Light Absorption Behaviors of Prismatic Titanium-Oxo Clusters Containing Lacunary Lindqvist-like Species.

Exploring new structural types of polyoxotitanium clusters (PTCs), especially those containing classical polyoxometalates structures, has always been the focus of research in the field of metal-oxo clusters. In this work, we present the synthesis and characterization of three prismatic PTCs: namely, Ti 8 (μ 2 -O) 3 (μ 4 -O) 2 (O n Pr) 6 (HO n Pr) 2 (L1) 8 ( PTC-237 ; H 2 L1 = 3,5-di- tert -butylcatechol), Ti 12 (μ 2 -O) 6 (μ 3 -O) 8 (O n Pr) 6 (L2) 12 (L3) 2 ( PTC-238 ; HL2 = 1-adamantanecarboxylic acid, HL3 = 2-picolinic acid), and [Ti 18 (μ 2 -O) 4 (μ 3 -O) 16 (μ 5 -O) 2 (O i Pr) 18 (L3) 8 ](L3) 2 ( PTC-239 ). Single-crystal X-ray diffraction analyses indicate that the construction of these prismatic PTCs is based on a stepwise interlayer assembly of {Ti 3 } and {Ti 4 } substructures. The diameters of their core skeletons are in the range between 0.9 and 1.3 nm. In particular, lacunary Linqvist-like {Ti 4 } and {Ti 5 } building units are found to exist in the structures of PTC-237 and PTC-239 . According to the solid-state UV-vis diffuse reflectance measurements, the absorption band of 3,5-di- tert -butylcatecholate-functionalized PTC-237 shifts toward the visible-light region, giving a smaller optical band gap of 1.56 eV in comparison to PTC-238 (3.36 eV) and PTC-239 (3.25 eV).