Abstract
The dinuclear complexes (μ-H2L)Ru(bpy)22(ClO4)2 (3(ClO4)2), (μ-H2L)Ru(pap)22(ClO4)2 (4(ClO4)2), and the asym. (bpy)2Ru(m-H2L)Ru(pap)2(ClO4)2 (5(ClO4)2) were synthesized via the mononuclear species Ru(H3L)(bpy)2ClO4 (1ClO4) and Ru(H3L)(pap)2ClO4 (2ClO4), where H4L is the centrosym. 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochem. of the structurally characterized 1ClO4, 2ClO4, 3(ClO4)2, 4(ClO4)2, and 5(ClO4)2 reveals multistep oxidn. and redn. processes, which were analyzed by EPR of paramagnetic intermediates and by UV-visible-NIR spectro-electrochem. With support by time-dependent d. functional theory (DFT) calcns. the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 33+ vs. largely bridge-centered spin in 43+-a result of the presence of RuII-stabilizing pap coligands. In addn. to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asym. system 53+ with about equal contributions from a radical bridge formulation. In comparison to the analogs with the deprotonated 1,4-diaminoanthraquinone isomer the centrosym. H2L2- bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites. on SciFinder(R)
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