Isovalent and Mixed-Valent Diruthenium Complexes [(acac)2RuII (μ-bpytz)RuII(acac)2] and [(acac)2RuII(μ-bpytz)RuIII(acac)2](ClO4) (acac = Acetylacetonate and bpytz = 3,6-Bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine):  Synthesis, Spectroelectrochemical, and EPR Investigation

The title compounds involving the structurally characterized bridging ligand bpytz were characterized, showing very strong electrochemical stabilization of the mixed-valent RuIIRuIII state (K c = 1013.9) but no detectable (ε < 20 M-1 cm-1) intervalence charge-transfer band in the infrared region. In situ reduction of the neutral precursor produces a diruthenium(II) complex of the bpytz radical anion according to EPR spectroscopy, whereas oxidation of the mixed-valent form leads to a diruthenium(III) species.