Optical Determination of Electron Transfer Dynamics and Kinetics for Asymmetrical [Mo2]–ph–[Mo2] Systems

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• 作者：Wei Yong Yu ; Miao Meng ; Hao Lei ; Xue Dan He ; Chun Y. Liu
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 16, 2016
• 年：2016
• 卷：120
• 期：23
• 页码：12411-12422
• 全文大小：577K
• 年卷期：0
• ISSN：1932-7455

文摘

We report the study, in terms of electronic coupling (EC) and electron transfer (ET), on three asymmetrical Mo₂ dimers [Mo₂(DAniF)₃]₂[μ-(NH)OCC₆H₄CO₂] ([NO–ph–OO]) (DAniF = N,N′-di(p-anisyl)formamidinate), [Mo₂(DAniF)₃]₂[μ-(NH)₂CC₆H₄CO₂] ([NN–ph–OO]), and [Mo₂(DAniF)₃]₂[μ-(NH)₂CC₆H₄C(NH)O] ([NN–ph–NO]), which are closely related to the three symmetrical analogues [OO–ph–OO], [NO–ph–NO], and [NN–ph–NN] reported earlier. The mixed-valence (MV) complexes [NO–ph–OO]⁺, [NN–ph–OO]⁺, and [NN–ph–NO]⁺ exhibit metal to ligand and ligand to metal charge transfer bands, along with an intervalence (IV) transition absorption in the Near-IR region. The free energy change (ΔG°) for ET is determined by comparing the redox potential splitting (ΔE_1/2) and IV transition energy (E_IT) with the data for the symmetrical species. The reorganization energy (λ) is estimated from the Hush model (Δν_1/2 = [16ln(2)λRT]^1/2). Significantly, electrochemical and optical analyses verify E_IT = ΔG° + λ, the core energetic relationship underlying the semiclassical theories. With the electronic coupling parameters calculated from the method suggested by Creutz, Newton and Sutin (H_MM′ = ∼ 500 cm^–1), the adiabatic ET rate constants k_et (f) are determined to be ∼10¹⁰ s^–1 for [NO–ph–OO]⁺ and [NN–ph–NO]⁺, smaller than k_et (r) for the backward reaction and k_et for the symmetrical analogues by 1 order of magnitude, and ∼10⁹ s^–1 for [NN–ph–OO]⁺. This work illustrates that the redox asymmetry in D–B–A systems controls the ET rate and direction.