Theoretical investigation of electronic properties and redox properties for purely inorganic and aryloxide substituted Ti-containing POM derivatives

Abstract

DFT calculations have been performed to investigate the redox properties and electron transition for a series of purely inorganic and aryloxide substituted Ti-containing polyoxometalate (POM) derivatives. The modification of organic conjugated groups dramatically alters the HOMO population and decreases the energy gap. It is evident from redox analysis that Ti atoms are preferred redox centres in organic–inorganic hybrid Ti-containing POMs, and the incorporation of π-conjugated groups evokes anodic shift for reduction potential. In contrast with mono-TiW₅O₁₈ derivatives, bi-TiW₅O₁₈ derivatives exhibit narrower energy gaps and more active redox properties. It is noteworthy that the attachment of π-conjugated groups induces the low-energy electron transition to be a significant bathochromic-shift, and it has been dramatically red-shifted by 296 nm in compound 1c in contrast with that in compound 1a. When the two TiW₅O₁₈ units are covalently linked as terminals to construct bi-TiW₅O₁₈ derivatives, the low-energy electron transition presents further bathochromical shift compared with corresponding mono-TiW₅O₁₈ derivatives. In addition, the crucial charge transfer for the hybrid Ti-containing POMs are generated from π-conjugated donor to d-Ti orbital with part of p–O_c orbitals. The incorporation of the organic substituents results in attached POMs by covalent linkage to the catalyst supports, which consequently enhances the ability of catalysis.

Keywords:

• electronic properties
• aryloxide substitution
• redox properties
• bathochromic-shift

Acknowledgements

The authors gratefully acknowledge the financial support from Program for Changjiang Scholars and Innovative Research Team in University (IRT0714), Department of Science and Technology of Jilin Province (20082103), the Training Fund of NENU's Scientific Innovation Project (NENU-STC07017), and Science Foundation for Young Teachers of Northeast Normal University (20090401). We also acknowledge YHK for computational support.

Notes

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