Manganese complexes semiquinones

In special circumstances the metal and a ligand can compete for the spin in a paramagnetic complex. As this alternative involves oxidation-state changes, it is referred to as valence tautomerization or redox isomerization [78]. Such behavior is observed for o-semiquinone complexes of cobalt and manganese [78] recently, a copper(I)-semiquinone-copper(II)-catecholate equilibrium system (7) of biochemical interest has been analyzed by temperature-dependent ESR [79]. 

The production of supramolecular polymers containing chromium tricarbonyl and manganese tricarbonyl moieties was deseribed."" Sweigart recently reported the self-assembly of r -quinone and r -semiquinone complexes derived from hydroquinone coordinated to cationic manganese tricarbonyl moieties." The metal-mediated deprotonation of these complexes allowed for the pro-duetion of polymers such as 16. 

The reaction of cobalt(II) salen complexes with -quinones results in the formation of a [cobalt(III)-(salen)-(t7-SQ)] complex, where ( >-SQ) represents the semiquinone radical ion. (Similar reactions are observed with iron(II) and manganese(II)-salen complexes, the reactions with these metal centers being more extensive than those for cobalt(II)). In the case of 3,5-di-rm-butyl-t>-benzoquinone, however, the cobalt(III) ligand radical complex has been isolated, and from hyperfine coupling constant studies which are assumed as diagnostic of the extent of electron transfer, the complex is described best as a low-spin cobalt(III) system with a coordinated semiquinone. 

Articles by Sweigart and coworkers have shown that manganese tricarbonyl complexes of r -hydroquinone deprotonate to give ii -semiquinone and q -quinone complexes. " " Solution NMR analysis and crystal structures of the q -semiquinone complex indicated that this complex was polymeric due to strong intermolecular hydrogen bonding, as shown in scheme 29 Reaction of the q -semiquinone and the q" -quinone complexes allowed the production of one-, two- and three-dimensional polymers. These complexes have also been shown to self-assemble by complexation of the oxygen atoms with transition metal ions. 

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