Effect of the Charge State (z = 鈭?, 0, +1) on the Nuclear Magnetic Resonance of Monodisperse Au25[S(CH2)2Ph]18z Clusters

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• 作者：Alfonso Venzo ; Sabrina Antonello ; Jose虂 A. Gasco虂n ; Ivan Guryanov ; Richard D. Leapman ; Neranjan V. Perera ; Alioscka Sousa ; Martina Zamuner ; Alessandro Zanella ; Flavio Maran
• 刊名：Analytical Chemistry
• 出版年：2011
• 出版时间：August 15, 2011
• 年：2011
• 卷：83
• 期：16
• 页码：6355-6362
• 全文大小：920K
• 年卷期：v.83,no.16(August 15, 2011)
• ISSN：1520-6882

文摘

Monodisperse Au₂₅L₁₈⁰ (L = S(CH₂)₂Ph) and [n-Oct₄N⁺][Au₂₅L₁₈^{鈥?/sup>] clusters were synthesized in tetrahydrofuran. An original strategy was then devised to oxidize them: in the presence of bis(pentafluorobenzoyl) peroxide, the neutral or the negatively charged clusters react as efficient electron donors in a dissociative electron-transfer (ET) process, in the former case yielding [Au₂₅L₁₈+][C₆F₅CO₂鈥?/sup>]. As opposed to other reported redox methods, this dissociative ET approach is irreversible, easily controllable, and clean, particularly for NMR purposes, as no hydrogen atoms are introduced. By using this approach, the 鈭?, 0, and +1 charge states of Au₂₅L₁₈ could be fully characterized by 1H and 13C NMR spectroscopy, using one- and two-dimensional techniques, in various solvents, and as a function of temperature. For all charge states, the NMR results and analysis nicely match recent structural findings about the presence of two different ligand populations in the capping monolayer, each resonance of the two ligand families displaying distinct NMR patterns. The radical nature of Au₂₅L₁₈0 is particularly evident in the 1H and 13C NMR patterns of the inner ligands. The NMR behavior of radical Au₂₅L₁₈0 was also simulated by DFT calculations, and the interplay between theory and experiments revealed a fundamental paramagnetic contribution coming from Fermi contact shifts. Interestingly, the NMR patterns of Au₂₅L₁₈鈥?/sup> and Au₂₅L₁₈+ were found to be quite similar, pointing to the latter cluster form as a diamagnetic species.}