Valence-state distribution in the ruthenium o-quinonoid systems [Ru(trpy)(Cl)(L-1)](+) and [Ru(trpy)(Cl)(L-2)](+) (L-1 = o-iminobenzoquinone, L-2 = o-diiminobenzoquinone; trpy=2,2 ': 6 ',2 ''-terpyridine)

摘要

Valence-state distributions in the ruthenium quinonoid (L) frameworks of [Ru(trpy)(Cl)(L-1))ClO4 (1-ClO4) and [Ru(trpy)-(CI) (L-2)]ClO4 (2-ClO4) (L-1 = o-iminobenzoquinone, L-2 = o-diiminobenzoquinone, and trpy = 2,2':6',2"-terpyridine) have been examined by structural, spectroelectrochemical, and density functional studies. The structural data, in corroboration with the DFT-calculated bond lengths, suggest that the primary valence formulation of 1(+) and 21 is a spin-coupled singlet configuration of [Ru-III(trpy)(Cl)(L-Sq)](+) with a minority contribution from diamagnetic [Ru-II(trpy)(Cl)(L-Q)](+). Consequently, the closely spaced successive two oxidation processes of 1(+) and 2(+) can be assigned to Ru-III -> Ru-IV and L-Sq -> L-Q, which involve the HOMO and HOMO-3 levels, respectively. The one-electron-oxidized species 1(2+) and 2(2+) display sharp EPR signals with g values of 2.011 and 2.014 at 77 K, respectively. The free radical EPR signal (g approximate to 2.0) of the one-electron-reduced species I or 2 signifies the preferential involvement of the ruthenium-based orbitals in the first reduction process to yield [Ru-II(trpy)(Cl)(L-Sq)], although the LUMO is calculated to be a mixture of d pi(Ru) (approximate to 24 %) and pi * (L) (approximate to 70 %). The subsequent second (1(-)/2(-)) and third (1(2-)/2(2-)) reduction steps in each case are associated simply with the terpyridyl-based orbitals (>= 90 %). The lowest energy charge-transfer transitions of 1(+) and 2(+) at 556 and 509 nm are predicted to be HOMO -> LUMO+1 and HOMO-1 -> LUMO+1 transitions, respectively. In the successive oxidations 1(+)/2(+) -> 1(2+)/2(2+) -> 1(3+)/2(3+) the lowest energy charge-transfer transitions undergo a blue shift with a substantial reduction in intensity. The lowest energy charge-transfer transitions, however, are red shifted with a reduction in intensity on going from (1(+)/2(+)) to 1/2. The origin of the transitions in the 1(2+)/2(2+) and 1/2 systems is predicted by TDDFT analysis. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)