Observation of the Strong Electronic Coupling in Near-Infrared-Absorbing Tetraferrocene aza-Dipyrromethene and aza-BODIPY with Direct Ferrocene−α- and Ferrocene−β-Pyrrole Bonds: Toward Molecular Machinery with Four-Bit Information Storage Capacity

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• 作者：Yuriy V. Zatsikha ; Cole D. Holstrom ; Kullapa Chanawanno ; Allen J. Osinski ; Christopher J. ZieglerVictor N. Nemykin
• 刊名：Inorganic Chemistry
• 出版年：2017
• 出版时间：January 17, 2017
• 年：2017
• 卷：56
• 期：2
• 页码：991-1000
• 全文大小：708K
• ISSN：1520-510X

文摘

The 1,3,7,9-tetraferrocenylazadipyrromethene (3) and the corresponding 1,3,5,7-tetraferrocene aza-BODIPY (4) were prepared via three and four synthetic steps, respectively, starting from ferrocenecarbaldehyde using the chalcone-type synthetic methodology. The novel tetra-iron compounds have ferrocene groups directly attached to both the α- and the β-pyrrolic positions, and the shortest Fe–Fe distance determined by X-ray crystallography for 3 was found to be ∼6.98 Å. These new compounds were characterized by UV–vis, nuclear magnetic resonance, and high-resolution electrospray ionization mass spectrometry methods, while metal–metal couplings in these systems were probed by electro- and spectroelectrochemistry, chemical oxidations, and Mössbauer spectroscopy. Electrochemical data are suggestive of the well-separated stepwise oxidations of all four ferrocene groups in 3 and 4, while spectroelectrochemical and chemical oxidation experiments allowed for characterization of the mixed-valence forms in the target compounds. Intervalence charge-transfer band analyses indicate that the mixed-valence [3]⁺ and [4]⁺ complexes belong to the weakly coupled class II systems in the Robin–Day classification. This interpretation was further supported by Mössbauer spectroscopy in which two individual doublets for Fe(II) and Fe(III) centers were observed in room-temperature experiments for the mixed-valence [3]ⁿ⁺ and [4]ⁿ⁺ species (n = 1–3). The electronic structure, redox properties, and UV–vis spectra of new systems were correlated with Density Functional Theory (DFT) and time-dependent DFT calculations (TDDFT), which are suggestive of a ferrocene-centered highest occupied molecular orbital and chromophore-centered lowest unoccupied molecular orbital in 3 and 4 as well as predominant spin localization at the ferrocene fragment attached to the α-pyrrolic positions in [3]⁺ and [4]⁺.