Journal
DALTON TRANSACTIONS
Volume -, Issue 45, Pages 10114-10121Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/b915946k
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Funding
- U. S. Department of Energy [DE-AC02-05CH11231]
- Department of Energy, Office of Biological and Environmental Research
- National Institutes of Health
- National Center for Research Resources
- Biomedical Technology Program
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An all-inorganic heterobinuclear chromophore consisting of Ti-IV oxo-bridged to a Mn-II center has been assembled on the surface of silica pores of MCM-41 material. The key step of covalent attachment on the pore surface is the reaction of a MnII precursor featuring weakly held CH3CN ligands with the OH group of a previously anchored titanol site. The optical diffuse reflectance spectrum reveals a (TiOMnII)-O-IV -> (TiOMnIII)-O-III metal-to-metal charge-transfer (MMCT) absorption extending from the UV throughout to visible into the red spectral region. FT-IR, FT-Raman and optical spectroscopy confirm that the material is free of Mn oxide clusters, while EPR and Mn K-edge X-ray absorption spectra indicate that the donor center is predominantly in oxidation state +2. In situ FT-IR spectroscopy allowed detection of visible light-induced redox chemistry of the MMCT unit using O-2 (O-18(2)) and methanol as acceptor and donor probe molecules, respectively. Formate and water were observed as primary products, with methyl formate emerging as a secondary condensation product. The observed photochemistry demonstrates that excitation of the TiIVOMnII. TiIIIOMnIII results in complete transfer of an electron from donor to acceptor center, with the charge separation sufficiently long lived for initiation of redox chemistry to occur. With donor and acceptor redox potentials appropriate for driving multi-electron catalysts for water oxidation, proton or CO2 reduction, the TiOMnII unit is an attractive candidate as a charge-transfer chromophore in a solar fuel generating system.
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