Characterization of the mixed-valent intermediate (n=3) of the complex series {(μ,η3:η3-L)[(Ru(terpy)]2}n+ with the unsaturated bridging ligand N,N′-bis(α-picolinoyl)hydrazido(2−)=L2−

N,N′-Bis(α-picolinoyl)hydrazine H2L, a potentially bis-tridentate conjugated ligand in its doubly deprotonated form L2−, has been used to synthesize the diruthenium(II) complex {(μ-L)[Ru(terpy)]2}(PF6)2. Its electrochemical and spectroelectrochemical (UV–Vis–NIR, EPR) investigation reveals a mixed-valent (RuIIIRuII) intermediate with electrochemical and spectroscopic characteristics related to those of the {(μ-adc-R)[Ru(bpy)2]2}3+ ions (adc-R2−=bis-bidentate C-substituted diacylhydrazido(2−) ligands): comproportionation constant Kc=109.0 (CH2Cl2), intervalence charge transfer band at 1000 nm (ε=3800 M−1 cm−1), EPR signal at g⊥=2.14, g∥=1.953. The non-innocent nature of Ln− is inferred from comparative analysis of the spectroscopic data.