The diamagnetic title complexes were obtained from Ru(acac)(2)(CH3CN)(2) and 2-aminophenol or 2-aminothiophenol. X-ray structure analysis of (L-1)Ru(acac)(2) (L-1 = o-iminoquinone) revealed C-C intra-ring, C-O, and C-N distances which suggest a Ru-III-iminosemiquinone oxidation state distribution with antiparallel spin-spin coupling. One-electron oxidation and reduction of both title compounds to paramagnetic monocations [(L)Ru(acac)(2)](+) or monoanions [(L)Ru(acac)(2)](-) occurs reversibly at widely separated potentials (DeltaE > 1.3 V) and leads to low-energy shifted charge transfer bands. In comparison with clearly established Ru-II-semiquinone or Ru-III-catecholate systems the g tensor components 2.23 > g(1) > 2.09, 2.16 > g(2) > 2.07, and 1.97 > g(3) > 1.88 point to considerable metal contributions to the singly occupied MO, corresponding to Ru-III complexes with either o-quinonoid (--> cations) or catecholate-type ligands (--> anions) and only minor inclusion of Ru-IV- or Ru-II-iminosemiquinone formulations, respectively. The preference for the Ru-III oxidation state for all accessible species is partially attributed to the monoanionic 2,4- pentanedionate (acac) co-ligands which favor a higher metal oxidation state than, e.g., neutral 2,2'-bipyridine (bpy).