Binuclear bis(.mu.-oxo)dimanganese(III,IV) and -(IV,IV) complexes with N,N'-bis(2-pyridylmethyl)-1,2-ethanediamine

Water Oxidation Catalyzed by a Dinuclear Mn Complex: A Functional Model for the Oxygen‐Evolving Center of Photosystem II

“…It is likely that during the 3!4 reaction step the carboxylate arms are concomitantly displaced to accommodate the two m-oxo ligands. Thus, an arrangement similar to other, known bis(moxo)-dimanganese complexes of linear N 4 bispicen-based [11] ligands (Mn···Mn = 2.7 ) [12][13][14] is achieved. The anticipated facile oxidation of 3 (oxidase activity) can be invoked to explain the slightly different curve shape in the first evolution step (the front of the peak shows a spike, which indicates an initial rapid reduction in O 2 concentration).…”

Considerations on the mechanism of photosynthetic water oxidation – dual role of oxo-bridges between Mn ions in (i) redox-potential maintenance and (ii) proton abstraction from substrate water

“…However, the short Mn-Mn distances found by EXAFS (Dau et al 2001;Robblee et al 2001) and EPR spectroscopy (Peloquin and Britt 2001) are highly suggestive of Mn ions that are electronically coupled, most likely via bridging oxygens. Consequently, any pure single-electron oxidation can be predicted to increase the redox potential for the next oxidation step significantly (increase by 0.6-1.0 V in di-l-oxo bridged Mn 2 complexes) (Goodson et al 1990; see Figures 2 and 3). In PS II, however, such an increase in redox-potential would prevent any subsequent oxidation of the Mn complex by Tyr Z .…”

Synthesis and Characterization of a Dinuclear Manganese(III,III) Complex with Three Phenolate Ligands

“…Absorption bands observed between 500 and 935 nm have been assigned to phenolate to Mn IV LMCT transitions in Mn IV monomeric complexes [20] as well as Mn 2 III,IV and Mn 2 IV,IV dimers [21] and bands at λ Ͼ 700 nm have been assigned to intervalence transitions in mixed-valence µ-oxo Mn 2 III,IV complexes. [22] Isosbestic points were observed at the outset (t Ͻ 300 s) of the spectroelectrochemical experiment (not shown). Throughout the course of electrolysis, however, the isosbestic points were not maintained either due to instability of the Mn 2 III,IV species or parallel formation of oxidation products from the second oxidation process.…”