Assembly of cyclic ferrocene-sensitized titanium-oxo clusters with excellent photoelectrochemical activity

Abstract

The development of crystalline titanium-oxo clusters has made great progress in recent years. However, the geometric assembly of titanium-oxo clusters is still very challenging. Herein, we report the assembly of two cyclic titanium-oxo clusters with ferrocene connectors, formulated as Ti₁₂(μ₃-O)₄(Fcdc)₄(OⁱPr)₃₂·0.5CH₂Cl₂ (Fcdc = 1,1′-ferrocenedicarboxylic acid; Ti₁₂Fcdc₄) and Ti₁₈(μ₂-O)₆(μ₃-O)₆(Fcdc)₂(L1)₂(L2)₄(OⁱPr)₃₄·2HOⁱPr (L1 = isonicotinic acid; L2 = salicylhydroxamic acid; Ti₁₈Fcdc₂). Single-crystal X-ray diffraction studies demonstrate that ferrocene with two carboxylic arms can adhere to the surface of {Ti₆} and/or {Ti₃} units, resulting in fascinating cyclic structures of Ti₁₂Fcdc₄ and Ti₁₈Fcdc₂. Notably, ferrocene ligands can not only serve as connectors to induce the geometric assembly of Ti-oxo clusters, but can also act as photosensitizers to greatly improve the light absorption behavior of the resulting compounds. Furthermore, the DFT calculation results suggest that the HOMO → LUMO transition mainly involves ferrocenyl group → Ti-oxo core charge transfer. Using the two ferrocene-containing clusters as electrode precursors, both electrodes exhibited excellent photocurrent responses. Our work opens a new way for the geometric assembly of titanium-oxo clusters and also contributes to the deep understanding of the structure–property relationships of sensitized Ti-based materials.