The new compounds [(acac)2Ru(μ-boptz)Ru(acac)2] (1), [(bpy)2Ru(μ-boptz)Ru(bpy)2](ClO4) 2 (2-(ClO4)2), and [(pap)2Ru(μ- boptz)-Ru(pap)2](ClO4)2 (3-(ClO 4)2) were obtained from 3,6-bis(2-hydroxyphenyl)-1,2,4,5- letrazine (H2boptz), the crystal structure analysis of which is reported. Compound 1 contains two antiferromagnetically coupled (J = -36.7cm1) RuIII centers. We have investigated the role of both the donor and acceptor functions containing the boptz2- bridging ligand in combination with the electronically different ancillary ligands (donating acac-, moderately π-accepting bpy, and strongly π-accepting pap; acac = acetylacetonate, bpy = 2,2′-bipyridine pap = 2-phenylazopyridine) by using cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy for several in situ accessible redox states. We found that metal-ligand-metal oxidation state combinations remain invariant to ancillary ligand change in some instances: however, three isoelectronic paramagnetic cores Ru(μ-boptz)-Ru showed remarkable differences. The excellent tolerance of the bpy coligand for both RuIII and RuII is demonstrated by the adoption of the mixed-valent form in [L2Ru(μ-boptz)-RuL2]3+, L = bpy, whereas the corresponding system with pap stabilizes the Ru II states to yield a phenoxyl radical ligand and the compound with L = acac- contains two RuIII centers connected by a tetrazine radical-anion bridge. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.