Electronic Coupling between Two Covalently Bonded Dimolybdenum Units Bridged by a Naphthalene Group

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• 作者：Guang Yuan Zhu ; Miao Meng ; Ying Ning Tan ; Xuan Xiao ; Chun Y. Liu
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：June 20, 2016
• 年：2016
• 卷：55
• 期：12
• 页码：6315-6322
• 全文大小：488K
• 年卷期：0
• ISSN：1520-510X

文摘

Using 2,6-naphthalenedicarboxylate and its thiolated derivatives as bridging ligands, three Mo₂ dimers of the type [Mo₂(DAniF)₃](E₂CC₁₀H₆CE₂)[Mo₂(DAniF)₃] (DAniF = N,N′-di-p-anisylformamidinate; E = O, S) have been synthesized and characterized by X-ray diffraction. These compounds can be generally formulated as [Mo₂]–naph–[Mo₂], where the complex unit [Mo₂] ([Mo₂(DAniF)₃(μ-E₂C)]) functions as an electron donor (acceptor) and the naphthalene (naph) group is the bridge. The mixed-valence (MV) complexes, generated by one-electron oxidation of the neutral precursors, display weak, very broad intervalence charge-transfer absorption bands in the near-to-mid-IR regions. The electronic coupling matrix elements for the MV complexes, H_ab = 390–570 cm^–1, are calculated from the Mulliken–Hush equation, which fall between those for the phenyl (ph) and biphenyl (biph) analogues reported previously. The three series consisting of three complexes with the same [Mo₂] units exhibit exponential decay of H_ab as the bridge changes from ph to biph via naph, with decay factors of 0.21–0.17 Å^–1. Therefore, it is evidenced that while the extent of the bridge conjugacy varies, the electronic coupling between the two [Mo₂] units is dominated by the Mo₂···Mo₂ separation. The absorption band energies for metal-to-ligand charge transfer are in the middle of those for the ph and biph analogues, which is consistent with variation of the HOMO–LUMO energy gaps for the complex series. These results indicate that the interplay of the bridge length and conjugacy is to affect the enegy for charge transfer crossing the intervening moiety, in accordance with a superechange mechanism.