Radical non-radical states of the [Ru(PIQ)] core in complexes (PIQ = 9,10-phenanthreneiminoquinone)

Abstract

9,10-Phenanthreneiminosemiquinonate anion radical (PIQ˙⁻) complexes of ruthenium of types trans-[Ru^II(PIQ˙⁻)(PPh₃)₂(CO)Cl] (1) and trans-[Ru^III(PIQ˙⁻)(PPh₃)₂Cl₂] (2) are reported. Reactions of 1 and 2 with I₂ afford trans-[Ru^III(PIQ˙⁻)(PPh₃)₂(CO)Cl]⁺I₃⁻·½CH₂Cl₂ (1⁺I₃⁻·½CH₂Cl₂) and trans-[Ru^III₂(PIQ˙⁻)₂(PPh₃)₂(μ-Cl)₃]⁺I₃⁻·¼I₂·¼toluene) (3⁺I₃⁻·¼I₂·¼toluene), while the reaction of 2 with Br₂ yields a 9,10-phenanthreneiminoquinone (PIQ) complex of the type mer-[Ru^III(PIQ)(PPh₃)Br₃]·½CH₂Cl₂ (4·½CH₂Cl₂). In comparison, the reaction of trans-[Ru^III(PQ˙⁻)(PPh₃)₂Cl₂] (2_PQ), a 9,10-phenanthrenequinone (PQ) analogue of 2 affords only trans-[Ru^III(PQ)(PPh₃)₂Cl₂]⁺Br₃⁻ (5⁺Br₃⁻). Considering the X-ray bond parameters, EPR spectra and the atomic spin densities obtained from the density functional theory (DFT) calculations, 1 is defined as a PIQ˙⁻ (average C–O/N and C–C lengths, 1.280(2) and 1.453(3) Å) complex of ruthenium(II) while 4 is a neutral PIQ (average C–O, C–N, C–C and C–O/N lengths, 1.248(7), 1.284(7), 1.485(8) and 1.266(7) Å) complex of the ruthenium(III) ion. The single crystal X-ray bond parameters proposed that 1⁺I₃⁻ (average C–O/N and C–C lengths, 1.294(8) and 1.449(9) Å) and 2 (average C–O/N and C–C lengths, 1.289(2) and 1.447(4) Å) are PIQ˙⁻ complexes of ruthenium(III), while the 3⁺ ion (average C–O/N and C–C lengths, 1.288 ± 0.004 and 1.450 ± 0.017 Å) is a co-facial bi-octahedral complex of ruthenium(III). In contrast, the 5⁺ ion is a PQ complex of the ruthenium(III) ion. EPR spectra and the calculated atomic spin densities authenticated that the 2⁺ ion obtained after constant potential coulometric oxidation of 2 is a PIQ complex of ruthenium(III), while the 2⁻ ion is a hybrid state of [Ru^II(PIQ˙⁻)] and [Ru^III(PIQ²⁻)] states. It is observed that the PIQ˙⁻ state in which spin is more localized on the nitrogen (∼38% in 1 and ∼35% in 2⁻ ion) is stable and the coordination of the PIQ²⁻ state is not observed in this study. Redox activities, UV-vis/NIR absorption spectra and their origins and the spectroelectrochemical measurements for 2 → 2⁺, 2 → 2⁻ and 3⁺ → 3²⁺ conversions are analyzed.