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(mu(2)-O)(3)(mu(4)-O)(2)(OnPr)(6)(HOnPr)(2)(L1)(8) (PTC-237; H(2)L1 = 3,5-di-tert-butyl-catechol), Ti-12(mu(2)-O)(6)(mu(3)-O)(8)(OnPr)(6)(L2)(12)( L3)(2) (PTC-238; HL2 = 1-adamantanecarboxylic acid, HL3 = 2-picolinic acid), and [Ti-18(mu(2)-O)(4)(mu(3)-O)(16)( mu(5)-O)(2)(OiPr)(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).