title: Experimental and DFT evidence for the fractional non-innocence of a β-diketonate ligand.
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 π-accepting pap ligand and the σ-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(-) → Ru(III)) and LL/CT (pap(⋅-) → 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+) ↔ [Ru(II)(pap(0))(2)(L(⋅))](2+) and [Ru(III)(pap(0))(L(-))(2)](+) ↔ [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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076 (India).
authors.forename: Amit
authors.initials: A
authors.lastname: Das
authors.forename: Thomas Michael
authors.initials: TM
authors.lastname: Scherer
authors.forename: Prasenjit
authors.initials: P
authors.lastname: Mondal
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri