Complexes with Tunable Intramolecular Ferrocene to TiIV Electronic Transitions: Models for Solid State FeII to TiIV Charge Transfer
| Autor: | Zikri Altun, Paul S. Wagenknecht, Alexis R. Myers, Elizabeth S. Carlton, Jeffrey J. Rack, Jared A. Pienkos, Carl Trindle, Michael D. Turlington, Karlee N. Wroblewski |
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| Rok vydání: | 2016 |
| Předmět: |
Trimethylsilyl
Metallocenes Stereochemistry 010402 general chemistry Electrochemistry 01 natural sciences Inorganic Chemistry Metal chemistry.chemical_compound Ferrous Compounds Physical and Theoretical Chemistry Spectroscopy Titanium 010405 organic chemistry Electrochemical Techniques 0104 chemical sciences Crystallography Models Chemical chemistry Ferrocene visual_art Intramolecular force visual_art.visual_art_medium Thermodynamics Spectrophotometry Ultraviolet Cyclic voltammetry Ferrocyanide Oxidation-Reduction |
| Zdroj: | Inorganic Chemistry. 55:2200-2211 |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | Iron(II)-to-titanium(IV) metal-to-metal-charge transfer (MMCT) is important in the photosensitization of TiO2 by ferrocyanide, charge transfer in solid-state metal-oxide photocatalysts, and has been invoked to explain the blue color of sapphire, blue kyanite, and some lunar material. Herein, a series of complexes with alkynyl linkages between ferrocene (Fc) and Ti(IV) has been prepared and characterized by UV-vis spectroscopy and electrochemistry. Complexes with two ferrocene substituents include Cp2Ti(C2Fc)2, Cp*2Ti(C2Fc)2, and Cp2Ti(C4Fc)2. Complexes with a single ferrocene utilize a titanocene with a trimethylsilyl derivatized Cp ring, (TMS)Cp, and comprise the complexes (TMS)Cp2Ti(C2Fc)(C2R), where R = C6H5, p-C6H4CF3, and CF3. The complexes are compared to Cp2Ti(C2Ph)2, which lacks the second metal. Cyclic voltammetry for all complexes reveals a reversible Ti(IV/III) reduction wave and an Fe(II/III) oxidation that is irreversible for all complexes except (TMS)Cp2Ti(C2Fc)(C2CF3). All of the complexes with both Fc and Ti show an intense absorption (4000 M(-1)cm(-1)ε8000 M(-1)cm(-1)) between 540 and 630 nm that is absent in complexes lacking a ferrocene donor. The energy of the absorption tracks with the difference between the Ti(IV/III) and Fe(III/II) reduction potentials, shifting to lower energy as the difference in potentials decreases. Reorganization energies, λ, have been determined using band shape analysis (2600 cm(-1)λ5300 cm(-1)) and are in the range observed for other donor-acceptor complexes that have a ferrocene donor. Marcus-Hush-type analysis of the electrochemical and spectroscopic data are consistent with the assignment of the low-energy absorption as a MMCT band. TD-DFT analysis also supports this assignment. Solvatochromism is apparent for the MMCT band of all complexes, there being a bathochromic shift upon increasing polarizability of the solvent. The magnitude of the shift is dependent on both the electron density at Ti(IV) and the identity of the linker between the titanocene and the Fc. Complexes with a MMCT are photochemically stable, whereas Cp2Ti(C2Ph)2 rapidly decomposes upon photolysis. |
| Databáze: | OpenAIRE |
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