Abstract
New compounds Ru(pap)(2)(L)(ClO(4)), Ru(pap)(L)(2), and Ru(acac)(2)(L) (pap = 2-phenylazopyridine, L(-) = 9-oxidophenalenone, acac(-) = 2,4-pentanedionate) have been prepared and studied regarding their electron-transfer behavior, both experimentally and by using DFT calculations. Ru(pap)(2)(L)(ClO(4)) and Ru(acac)(2)(L) were characterized by crystal-structure analysis. Spectroelectrochemistry (EPR, UV/Vis/NIR), in conjunction with cyclic voltammetry, showed a wide range of about 2 V for the potential of the Ru(III/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 versus SCE, the oxidation of L(-) into L(·) could be deduced from the near-IR absorption of Ru(III)(pap)(L(·))(L(-))(2+). Other intense long-wavelength transitions, including LMCT (L(-) $\rightarrow$ Ru(III)) and LL/CT (pap(·-) $\rightarrow$ L(-)) processes, were confirmed by TD-DFT results. DFT calculations and EPR data for the paramagnetic intermediates allowed us to assess the spin densities, which revealed two cases with considerable contributions from L-radical-involving forms, that is, Ru(III)(pap(0))(2)(L(-))(2+) $łeftrightarrow$ Ru(II)(pap(0))(2)(L(·))(2+) and Ru(III)(pap(0))(L(-))(2)(+) $łeftrightarrow$ Ru(II)(pap(0))(L(·))(L(-))(+). Calculations of electrogenerated complex Ru(II)(pap(·-))(pap(0))(L(-)) displayed considerable negative spin density (-0.188) at the bridging metal.on SciFinder (R)
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