Synthesis, Structures, and Photocurrent Responses of Polyoxo-Titanium Clusters with Oxime Ligands: From Ti4 to Ti18.

Six crystalline polyoxo-titanium clusters (PTCs) derived from oximes, namely, Ti4(μ4-O)(OMe)6(L1)4 (PTC-125; H2L1 = salicylaldoxime), H[Ti5(μ2-O)(μ3-O)2(OMe)3(L1)6] (PTC-126), Ti6(μ2-O)(μ3-O)2(O iPr)10(OAc)2(L2)2 (PTC-127; H3L2 = salicylhydroxamic acid; HOAc = acetic acid), Ti7(μ3-O)2(OEt)18(L2)2 (PTC-128), Ti12(μ2-O)4(μ3-O)4(OEt)20(L2)4 (PTC-129), and Ti18(μ2-O)10(μ3-O)8(μ4-O)2(OEt)30(L3)2 (PTC-130; HL3 = acetoxime) have been solvothermally synthesized and structurally characterized. Compared with the reported solid-state monomer, dimer, trimer, and tetramer titanium oximes, these compounds possess high nuclearity structures in the range Ti4, Ti5, Ti6, Ti7, Ti12, and Ti18 as a result of the presence of oxo bridges. Even though three examples of tetranuclear and hexanuclear derivatives have been documented, PTC-130 with a centrosymmetric Ti18 cluster core represents the currently highest PTC compound in the oxime system. In addition, Ti/oximate ratio by solvothermal synthesis in this work possessed a broad range from 0.83:1 to 9:1, different from the constant ratio of 1:1 in the reported ones. According to the solid-state UV-vis diffuse reflectance measurement, the existence of oxime ligands largely enhanced their visible light harvest. Furthermore, their photocurrent response properties are also studied.