Substituent Effects on Core Structures and Heterogeneous Catalytic Activities of MnIII(渭-O)2MnIV Dimers with 2,2鈥?6鈥?2鈥?Terpyridine Derivative Ligands for Water Oxidat

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• 作者：Hirosato Yamazaki ; Satoshi Igarashi ; Toshi Nagata ; Masayuki Yagi
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 6, 2012
• 年：2012
• 卷：51
• 期：3
• 页码：1530-1539
• 全文大小：531K
• 年卷期：v.51,no.3(February 6, 2012)
• ISSN：1520-510X

文摘

[(OH₂)(R-terpy)Mn(渭-O)₂Mn(R-terpy)(OH₂) ]³⁺ (R-terpy = 4鈥?substituted 2,2鈥?6鈥?2鈥?terpyridine, R = butoxy (BuO), propoxy (PrO), ethoxy (EtO), methoxy (MeO), methyl (Me), methylthio (MeS), chloro (Cl)) have been synthesized as a functional oxygen-evolving complex (OEC) model and characterized by UV鈥搗is and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. The UV鈥搗is spectra of derivatives in water were hardly influenced by the 4鈥?substituent variation. X-ray crystallographic data showed that Mn centers in the Mn^III(渭-O)₂Mn^IV cores for derivatives with R = H, MeS, Me, EtO, and BuO are crystallographically indistinguishable, whereas the derivatives with R = MeO and PrO gave the significantly distinguishable Mn centers in the cores. The indistinguishable Mn centers could be caused by rapid electron exchange between the Mn centers to result in the delocalized Mn(渭-O)₂Mn core. The exchange integral values (J = 鈭?96 to 鈭?78 cm^鈥?) for delocalized cores were lower than that (J = 鈭?63 to 鈭?61 cm^鈥?) for localized cores, though the Mn路路路Mn distances are nearly the same (2.707鈥?.750 脜). The half wave potential (E_1/2) of a Mn^III鈥揗n^IV/Mn^IV鈥揗n^IV pair of the derivatives decreased with an increase of the electron-donating ability of the substituted groups for the delocalized core, but it deviated from the correlation for the localized cores. The catalytic activities of the derivatives on mica for heterogeneous water oxidation were remarkably changed by the substituted groups. The second order rate constant (k₂/mol^鈥? s^鈥?) for O₂ evolution was indicated to be correlated to E_1/2 of a Mn^III鈥揗n^IV/Mn^IV鈥揗n^IV pair; k₂ increased by a factor of 29 as E_1/2 increased by 28 mV.