Neutral spin-delocalized mixed-valence manganese(I)-manganese(II) dimers bridged by alkoxide, imidazolate, or malonodinitrile anions
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Inorganic Chemistry 25 (27): 4865--4870 (1986)

(h5-C5H4Me)(CO)2Mn2(m-L) L = Me3CO-, 1-adamantyl oxide, imidazolate, Me3CC(CN)2-, HC(CN)2- were prepd. from Mn precursor complexes by oxidn. with air or PbO2 in aprotic media and were characterized by ESR as spin-delocalized Mn(I)Mn(II) systems. Stability and extent of formation of these dimers depend on the s-donor strength of the anionic bridging ligands and correlate with their basicity, the alkoxides being the strongest and the malonodinitrile anions the weakest bases. A comparison of the mixed-valence dimers with corresponding mononuclear low-spin Mn(II) complexes (h5-C5H4Me)(CO)2(L)Mn reveals similar g values and halving of the 55Mn coupling consts., except for the alkoxide-bridged dimers, which exhibit some metal-metal interaction. Intervalence transitions (IT) of the imidazolate and malonodinitrile anion bridged Mn(I)Mn(II) dimers in toluene soln. are remarkably similar to the IT features measured for corresponding Ru(II)Ru(III) ammine complexes in aq. solns. The significance of the spectroscopic results with regard to photosynthetic O2-evolving Mn centers is briefly discussed. on SciFinder(R)
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