Abstract
[Ru(pap)2(L)](ClO4), [Ru(pap)(L)2], and [Ru(acac)2(L)] (pap = 2-phenylazopyridine, L- = 9-oxidophenalenone, acac- = 2,4-pentanedionate) were prepd. and studied regarding their electron-transfer behavior, both exptl. and by using DFT calcns. [Ru(pap)2(L)](ClO4) and [Ru(acac)2(L)] were characterized by crystal-structure anal. Spectroelectrochem. (EPR, UV/visible/NIR), in conjunction with cyclic voltammetry, showed a wide range of $\sim$2 V for the potential of the RuIII/II couple, which was in agreement with the very different characteristics of the strongly p-accepting pap ligand and the s-donating acac- ligand. At the rather high potential of +1.35 V vs. SCE, the oxidn. of L- into L.bul. could be deduced from the near-IR absorption of [RuIII(pap)(L.bul.)(L-)]2+. Other intense long-wavelength transitions, including LMCT (L-$\rightarrow$RuIII) and LL/CT (pap.bul.-$\rightarrow$L-) processes, were confirmed by TD-DFT results. DFT calcns. and EPR data for the paramagnetic intermediates allowed the authors to assess the spin densities, which revealed two cases with considerable contributions from L-radical-involving forms, i.e., [RuIII(pap0)2(L-)]2+$łeftrightarrow$[RuII(pap0)2(L.bul.)]2+ and [RuIII(pap0)(L-)2]+$łeftrightarrow$[RuII(pap0)(L.bul.)(L-)]+. Calcns. of electrogenerated [RuII(pap.bul.-)(pap0)(L-)] displayed considerable neg. spin d. (-0.188) at the bridging metal. [on SciFinder(R)]
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