Valence structures of the diastereomeric complexes meso- and rac-[Ru2(acac)4(μ-Q)]n (n = 2−, 1−, 0, 1+, 2+) with the multiple quinonoid bridging ligand Q = 1,2,4,5-tetraimino-3,6-diketocyclohexane

Abstract

Meso- and rac-configurated diastereoisomers [Ru(2)(acac)(4)(mu-Q)] have been separated and identified as Ru(II)-Q(0) species through a crystal structure analysis of the meso form. The presence of two redox-active {Ru(acac)(2)} groups (acac(-) = 2,4-pentanedionate) and quinonoid Q with two equivalent pi-conjugated alpha-diimine chelate sites and one p-quinone function allowed for the full cyclic voltammetric and spectroelectrochemical (UV-vis-NIR, IR, EPR) characterisation of the five accessible states (2-, 1-, 0, 1+ and 2+ forms) for both isomers. Oxidation occurs at the metal ions to produce Ru(II)Ru(III) mixed-valent states [Ru(2)(acac)(4)(mu-Q)](+) (K(c) approximately 10(4.5)) with corresponding EPR features but without detectable intervalence absorption in the near infrared region. IR-spectroelectrochemistry reveals opposite frequency shifts for the nu(C=O) and nu(NH) stretching vibrations on reduction and oxidation, in agreement with the assumed electronic structure. Reduction leads to strongly stabilised [Ru(2)(acac)(4)(mu-Q)](-) states (K(c) approximately 10(11)) which show weak NIR shoulders around 1040 nm. The EPR characteristics are remarkably different for the two isomeric monoanions, reflecting presumably flexible geometry and electronic structure. The observation of broad but detectable EPR resonance at room temperature in solution and the g factor anisotropy in the glassy frozen state at 110 K suggest a rather evenly metal-ligand mixed singly occupied MO. Together with the ZINDO calculations and the partial experimental results reported previously by Masui et al. (Inorg. Chem., 2000, 39, 141) for [Ru(2)(bpy)(4)(mu-Q)](n+) (n = 2, 3, 4), the characteristic differences provide an insight into the electronic features such as mixed valency manifestations and the variable extent of mixing of the metal-quinone frontier orbitals of these systems involving Ru(II)-stabilised Q which is unknown as a free ligand.

Questions of Noninnocence and Ease of Azo Reduction in Diruthenium Frameworks with a 1,8-Bis((E)-phenyldiazenyl)naphthalene-2,7-dioxido Bridge

“…Diastereomeric 1 n and 2 n exhibited similar spectral profiles; however, they could easily be discerned by their distinctly different intensities ( 1 n > 2 n ), as had also been noted earlier in analogous systems. , The origin of transitions was evaluated by TD-DFT calculations for representative 2 n , 3 n , and 4 n , which revealed severe mixing of metal- and ligand-based orbitals due to intrinsic covalent features (Figures and and Figures S15 and S16 and Table S26 in the Supporting Information). The Ru­(III)-derived complex [(acac) 2 Ru III (μ-L 2– )­Ru II (acac) 2 ] ( 2 ) displayed ligand (L/acac) to metal charge transfer (LMCT) transitions in the visible region.…”

In Vitro Studies of the Activity of Dithiocarbamate Organoruthenium Complexes against Clinically Relevant Fungal Pathogens

“…Analysing the EPR results (Figure 2) for the prepared dithiocarbamate complexes, typical EPR signalw of ruthenium(III) ions in the low spin 4d 5 configuration can be seen, as shown in Figure 2 (for complexes C2 (Figure 2a) and C4 (Figure 2b)); the spike at 3,400 G ( g ≈ 2.00) in Figure 2b is probably due to an organic decomposition product. It can be suggested that the obtained ruthenium compounds correspond to Ru(II)/Ru(III) mixed-valent states complexes, similar to a species already described in the literature, [Ru 2 (acac) 4 (μ-Q)] + , where acac = 2,4-pentanedionate, and Q is a quinonoid group, with two equivalent π-conjugated α-diimine chelate sites, and one p -quinone function [64]. Those species can have different oxidation states accessible due to an intramolecular electron transfer, forming [Ru III (μ-Q 2 − )Ru II ] or [Ru II (μ-Q •− )Ru II ].…”

A Diruthenium Complex of a “Nindigo” Ligand

“…Aerial oxidation is assumed during the formation of 1 from reduced components, which is well-known to occur for dihydro compounds under basic conditions. 12 Side products accounting for 40% yield could not be removed from the column during chromatography. The use of dehydronindigo 7a gave essentially identical results.…”