Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(III,II) complex with an unusual arrangement of the bridging ligands

Syntheses, crystal structures and MMCT properties of diruthenium-based cyanido-bridged RuV/VI2-NC-RuII complexes

The goal of this study was to investigate how the electron-donating capability around the lower valent metal ion and the electron-accepting capability of the higher valent metal ion influence metal to metal charge transfer (MMCT) properties in mixed-valence complexes. A series of trinuclear ruthenium complexes represented as [Ru2(ap-4-Me)3(CH3COO)NCRuCpMex(dppe)][PF6] (CpMex = polymethylcyclopentadienyl, x = 0, 1, and 5; and dppe = 1, 2-bis(diphenylphosphino)ethane, ap-4-Me = 2-anilino-4-methylpyridine) and their one-electron oxidized products were synthesized and fully characterized. The UV-vis-NIR spectra confirmed that as the electron donor character of the CpMex(dppe)RuCN fragment enhanced or the electron-accepting capability of the higher valent diruthenium cluster increased, the RuII → RuV2 or RuVI2 Ru2 MMCT bands shifted to lower energies, which was supported by TDDFT calculations.

New insights into progressive ligand replacement from [Ru2Cl(O2CCH3)4]: synthetic strategies and variation in redox potentials and paramagnetic shifts

The complete series of [Ru₂Cl(Dp-FPhF)_x(O₂CCH₃)_4-x] (x = 1-4; Dp-FPhF^- = N,N'-bis(4-fluorophenyl)formamidinate) compounds, has been prepared and characterized by a multi-technique approach, including single crystal X-ray diffraction. A careful study of the different methodologies has allowed us to prepare four compounds with good yields and without an inert atmosphere or further purification. Specifically, [Ru₂Cl(Dp-FPhF)(O₂CCH₃)₃] (1) was obtained using an ultrasound-assisted (USS) method, while [Ru₂Cl(Dp-FPhF)₄] (4) was prepared by microwave assisted solvothermal synthesis (MWS). The intermediate substitution products cis-[Ru₂Cl(Dp-FPhF)₂(O₂CCH₃)₂] (2) and [Ru₂Cl(Dp-FPhF)₃(O₂CCH₃)] (3) have been prepared by conventional heating, controlling the molar ratio of the starting materials. ESI-MS and infrared spectroscopy were used to follow all the reactions and permitted a qualitative evaluation of the axial reactivity in this series. Magnetic and absorption measurements confirmed a high spin σ²π⁴δ²(π*δ*)³ electronic configuration in all cases. However, the effect of the gradual modification of the electronic density in the diruthenium core markedly affects other properties. The cyclic voltammograms of the compounds show a strong decrease in the one electron oxidation potential and an increase in the reduction potential in the series from 1 to 4. Furthermore, despite their paramagnetic nature, ¹H- and ¹⁹F-NMR spectra were recorded, and a correlation between the paramagnetic shift of the signals and the substitution degree of the diruthenium species was observed. These results provide a comprehensive guide to synthesise and understand the effects of equatorial ligand substitution on the properties of Ru₂⁵⁺ compounds.

Synthesis, Structural and Physicochemical Properties of Water-Soluble Mixed-Ligand Diruthenium Complexes Containing Anilinopyridinate Bridging Ligands

A series of water-soluble Ru₂⁵⁺ complexes of the type Ru₂(O₂CCH₃)₃(L)Cl where L = 2,3,4,5,6-F₅ap, 2,4,6-F₃ap, 2-Fap, ap, 2-Meap, 2,6-Me₂ap, or 2,4,6-Me₃ap, where ap is the anilinopyridinate anion, have been characterized as to their structural and physicochemical properties in H₂O and DMSO. Five of the newly synthesized complexes were structurally characterized, and the Ru-Cl bond lengths range from 2.477 to 2.544 Å while the Ru-Ru bond lengths range from 2.2838 to 2.2935 Å. The UV-vis spectra of each compound are characterized by three absorption bands in both H₂O and DMSO, the intensity and position of which vary with both the type of bridging ligand and the solvent. The seven examined Ru₂⁵⁺ complexes exist as 1:1 electrolytes in water, and each undergoes a reversible one-electron reduction assigned to Ru₂⁵⁺/Ru₂⁴⁺ in both investigated solvents. A second irreversible reduction attributed to Ru₂⁴⁺/Ru₂³⁺ is also observed for each compound at more negative potentials in DMSO. A linear free energy relationship exists between the sum of the Hammett substituent constants (Σσ) on the ap-type bridging ligand and the wavenumber of an absorption band for the Ru₂⁵⁺ complexes. A linear relationship is also seen between Σσ and measured E_1/2 values for the Ru₂⁵⁺/Ru₂⁴⁺ process in water containing 0.1 M KCl, but little to no effect is seen between the specific bridging ligand and the structural features of the investigated compounds.

Structural, spectroscopic and electronic properties of a family of face-shared bi-octahedral Ru25+/6+ complexes with a bridging 2,5-di(2-pyridyl)pyrrolide ligand

Herein, we found that nitrogen donor dpp⁻ligand is flexible and provides a platform for aggregation of Ru²⁺ and/or Ru³⁺ to give a new type of face-sharing bi-octahedra Ru₂⁵⁺ and Ru₂⁶⁺ dimer featuring of distinct metal–metal bond bond between two ruthenium centres.

Effect of axial ligands on the spectroscopic and electrochemical properties of diruthenium compounds

Three related diruthenium complexes containing four symmetrical anionic bridging ligands were synthesized and characterized as to their electrochemical and spectroscopic properties. The examined compounds are represented as Ru2(dpb)4Cl, Ru2(dpb)4(CO), and Ru2(dpb)4(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru2(dpb)4Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru2(5+) form of the compound undergoes multiple redox processes involving the dimetal unit. The reversibility as well as potentials of these diruthenium-centered electrode reactions depends upon the solvent and the bound axial ligand. The Ru2(5+/4+) and Ru2(5+/6+) processes of Ru2(dpb)4Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru2(dpb)4Cl to [Ru2(dpb)4(CO)](+) was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru2(dpb)4Cl at room temperature. The chemically generated [Ru2(dpb)4(CO)](+) complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO4 under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru2(dpf)4(CO) in CH2Cl2, 0.1 M TBAClO4 under a N2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru2(dpb)4(NO) undergoes two successive one-electron reductions and a single one-electron oxidation, all of which involve the diruthenium unit. The CO and NO adducts of Ru2(dpb)4 were further characterized by FTIR spectroelectrochemistry, and the IR spectral data of these compounds are discussed in light of results for previously characterized Ru2(dpf)4(CO) and Ru2(dpf)4(NO) derivatives under similar solution conditions.