Theoretical and experimental evidence for a new kind of spin-coupled singlet species: Isomeric mixed-valent complexes bridged by a radical anion ligand. Angewandte Chemie, International Edition, (44)35:5655--5658, 2005. [PUMA: acetylacetonate azobispyridine complex complex;electrochem complex;electronic complex;geometry complex;ruthenium crystal isomeric optimized prepn redox ruthenium structure]