A solvent- and temperature-dependent intramolecular equilibrium of diamagnetic and paramagnetic states in Co complexes bearing triaryl amines
| Autor: | Heinrich Lang, Holm Petzold, Evgenia Dmitrieva, Marco Rosenkranz, Linda Schnaubelt |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
010405 organic chemistry
Spin transition 010402 general chemistry 01 natural sciences Redox 0104 chemical sciences law.invention Inorganic Chemistry Crystallography chemistry.chemical_compound Electron transfer Paramagnetism chemistry law Proton NMR Cyclic voltammetry Electron paramagnetic resonance Acetonitrile |
| Zdroj: | Dalton transactions (Cambridge, England : 2003). 47(37) |
| ISSN: | 1477-9234 |
| Popis: | Complexes [Co(L)2](ClO4)2 (L = o-substituted 2-(pyridine-2-yl)-1,10-phenanthrolines 1a–c) containing three redox active centres (a Co2+ ion and two triaryl amine (Tara) units) have been synthesised. The order of oxidation steps in [Co(L)2](ClO4)2 (L = 1a–c) was determined using cyclic voltammetry and EPR/UV-vis-NIR spectroelectrochemistry. In acetonitrile solutions, at room temperature, the first oxidation is Co-centred followed by the Tara oxidation at more anodic potentials. The order of oxidation is inverted in solutions of the less polar solvent dichloromethane. The Co3+/2+-centred redox event leads to a spin transition between the paramagnetic high-spin (HS) Co2+ and the diamagnetic low-spin (LS) Co3+ state, which was proven using 1H NMR and EPR spectroscopy. After one-electron oxidation of [Co(L)2](ClO4)2, an equilibrium between the diamagnetic [Co3+(L)]3+ and paramagnetic [Co2+(L)(L+)]3+ state in [Co(L)2]3+ (L = 1a–c) was found. Cyclic voltammetry showed enhanced intermolecular electron transfer between the [Co2+(L)2]2+ and [Co3+(L)2]3+ redox states mediated by [Co2+(L)(L+)]3+. Variable temperature vis-NIR spectroscopy of in situ generated [Co(L)2]3+ revealed a temperature-dependent redox equilibrium between the [Co3+(L)2]3+ and the [Co2+(L+)(L)]3+ states (L = 1a–c). Magnetic coupling between the HS-Co2+ ion and the Tara+ radical in [HS-Co2+(L+)(L)]3+ (L = 1a,c) was deduced from broad and undetectable lines observed in the corresponding EPR spectra. Complete oxidation to [LS-Co3+(L+)2]5+ (L = 1a,c) leads to characteristic EPR spectra of Tara biradicals with non-interacting spins. |
| Databáze: | OpenAIRE |
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