Synthesis and Characterization of Tris(bipyridyl)ruthenium(II)-Modified Mono-, Di-, and Trinuclear Manganese Complexes as Electron-Transfer Models for Photosystem II
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- 作者：Dirk Burdinski ; Eberhard Bothe ; and Karl Wieghardt
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：January 10, 2000
- 年：2000
- 卷：39
- 期：1
- 页码：105 - 116
- 全文大小：314K
- 年卷期：v.39,no.1(January 10, 2000)
- ISSN：1520-510X
文摘
With the aim of modeling the arrangement of redox-active and photoactive components along the electron-transferpathway of photosystem II, tetra- to nonanuclear transition metal complexes have been synthesized, comprisingone, two, or three manganese ions, oxidizable phenolates, and tris(2,2'-bipyridyl)ruthenium(II)-type units asphotosensitizers. These model complexes are considered to be mononuclear ([LnMn](PF6)m), dinuclear ([L1aMnIV2(
-O)2](PF6)6), or trinuclear ([LnMnIIMnIIMnIILn](PF6)12) with respect to the number of manganese centers present.Electronic coupling between the manganese ions is strongly antiferromagnetic in the case of the di(-oxo)dimanganese compound [L1aMnIV2(-O)2](PF6)6, where the "ligand" [H2L1a]4+ consists of two tris(bipyridyl)ruthenium(II)-type units covalentely bound to a bismacrocyclic Me2dtne backbone to which the manganese ionsare coordinated via an additional phenolate oxygen (Me2dtne = 1,2-bis(4-methyl-1,4,7-triazacyclononyl)ethane).Weak antiferromagnetic coupling is observed in compounds [LnMnIIMnIIMnIILn](PF6)12, where the three metalsare in a linear arrangement (face-sharing octahedral). They are bridged by three phenolate oxygens of each of thedeprotonated "ligands" [H3Ln]6+, respectively. Each ligand [H3Ln]6+ (n = 1, 2) consists of a tacn ring with threependent arm phenols which are each bound to a tris(bipyridyl)ruthenium(II)-type unit (tacn = 1,4,7-triazacyclononane). In these compounds several electron-transfer steps were detected by electrochemical methodswhich are assigned to different redox processes located at individual electrochemically active components (Mn,Ru, bipyridyl, phenolate). For example, in the "mononuclear" compounds [LnMn](PF6)m (n = 1 or 2) Mn(II),Mn(III), and Mn(IV) are accessible and three Ru(II) centers are reversibly oxidized to Ru(III), and in addition,the coordinated phenolate can be oxidized to a highly reactive, coordinated phenoxyl radical. In several casesvery slow heterogeneous electron-transfer rates were observed for redox processes involving the manganese centers.
-O)2](PF6)6), or trinuclear ([LnMnIIMnIIMnIILn](PF6)12) with respect to the number of manganese centers present.Electronic coupling between the manganese ions is strongly antiferromagnetic in the case of the di(-oxo)dimanganese compound [L1aMnIV2(-O)2](PF6)6, where the "ligand" [H2L1a]4+ consists of two tris(bipyridyl)ruthenium(II)-type units covalentely bound to a bismacrocyclic Me2dtne backbone to which the manganese ionsare coordinated via an additional phenolate oxygen (Me2dtne = 1,2-bis(4-methyl-1,4,7-triazacyclononyl)ethane).Weak antiferromagnetic coupling is observed in compounds [LnMnIIMnIIMnIILn](PF6)12, where the three metalsare in a linear arrangement (face-sharing octahedral). They are bridged by three phenolate oxygens of each of thedeprotonated "ligands" [H3Ln]6+, respectively. Each ligand [H3Ln]6+ (n = 1, 2) consists of a tacn ring with threependent arm phenols which are each bound to a tris(bipyridyl)ruthenium(II)-type unit (tacn = 1,4,7-triazacyclononane). In these compounds several electron-transfer steps were detected by electrochemical methodswhich are assigned to different redox processes located at individual electrochemically active components (Mn,Ru, bipyridyl, phenolate). For example, in the "mononuclear" compounds [LnMn](PF6)m (n = 1 or 2) Mn(II),Mn(III), and Mn(IV) are accessible and three Ru(II) centers are reversibly oxidized to Ru(III), and in addition,the coordinated phenolate can be oxidized to a highly reactive, coordinated phenoxyl radical. In several casesvery slow heterogeneous electron-transfer rates were observed for redox processes involving the manganese centers.