Modulating the band gap and photoelectrochemical activity of dicarboxylate-stabilized titanium-oxo clusters

Abstract

The dicarboxylate-stabilized titanium-oxo clusters (TOCs) [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(BDC)2(O2CFc)2] (C1), [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(TFBDC)2(O2CFc)2] (C2), and [Ti6(μ3-O)4(μ2-OiPr)2(OiPr)8(BDC)2(O2CC6H5)2] (C3) (BDC = 1,2-benzenedicarboxylate, TFBDC = 3,4,5,6-tetrafluoro-1,2-benzenedicarboxylate, Fc = ferrocenyl) were synthesized and structurally characterized. The band gap and photoelectrochemical (PEC) activity of the three Ti6-oxo clusters were effectively modulated by electronic effects of the peripheral carboxylate ligands. Moreover, with the same Ti6O4 core structure, the electronic transitions induced by the functional ligands can be clearly elucidated by combined experimental and computational studies. It is reveal that the low-energy transitions of the ferrocene-containing clusters C1 and C2 mainly involve the Fe 3d → Ti6O4 core metal-to-core charge transfer (MCCT) transition. The introduction of ferrocenecarboxylate ligands into the Ti6-oxo clusters significantly reduced the band gap to 2.2 eV (C1) and 1.9 eV (C2) relative to that of 3.6 eV for the benzoate substituted cluster C3. The electron-withdrawing effect of the TFBDC ligand remarkably promotes the PEC activity of C2.