Redox properties and electron transfer in a triarylamine-substituted HS-Co2+/LS-Co3+redox couple.
A new tridentate phenanthroline-pyridyl-based ligand 1 containing a redox active Tara (triaryl amine) unit has been developed (1 = 4-((6-(1,10-phenanthrolin-2-yl)pyridin-2-yl)oxy)-N,N-di-p-tolylaniline). The complex [Co2+(1)2](ClO4/BF4)2was prepared and the order of the oxidation steps was analysed by cyclic voltammetry and EPR/UV-vis-NIR spectroelectrochemistry. Oxidation of [Co2+(1)2]2+to [Co3+(1+)2]5+proceeds in two steps. The first step is the Co2+/3+centred oxidation to [Co3+(1)2]3+(E°'(M2+/3+) = 284 mV vs. Fc/Fc+) followed by oxidation of the Tara0/+centres (E°'(Tara) = 531 mV). Both kinds of oxidation processes were independently investigated in the analogous complexes [Zn(1)2](ClO4)2and [Co(2)2](BF4)2allowing an assignment of changes in the electronic spectra to the redox states (2 = 2-(6-phenoxypyridin-2-yl)-1,10-phenanthroline). Although spectroelectrochemistry did not indicate substantial coupling between the redox centres the Tara unit is an efficient mediator for the self-exchange in the [Co2+/3+(1)2]2+/3+couple. The electron transfer by self-exchange in [Co2+/3+(1)2]2+/3+was further investigated by variable temperature (VT)1H NMR spectroscopy. In addition, the resonances found in the paramagnetic proton NMR spectra were assigned by using COSY, T1and EXSY measurements in combination with the Co-N distances obtained from X-ray analysis. [Co(1)2]2+is found in the HS state. In contrast, the Fe2+species [Fe(1)2](ClO4)2is a spincrossover system. The SCO was analysed in solution by VT1H NMR and VT/vis spectroscopy.
TU Chemnitz, Institut für Chemie, Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany. holm.petzold@chemie.tu-chemnitz.de.
Linda
L
Schnaubelt
TU Chemnitz, Institut für Chemie, Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany. holm.petzold@chemie.tu-chemnitz.de.
Holm
http://orcid.org/0000-0002-0516-8692
H
Petzold
TU Chemnitz, Institut für Chemie, Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany. holm.petzold@chemie.tu-chemnitz.de.
J Matthäus
JM
Speck
Center of Spectroelectrochemistry, Leibniz Institute for Solid State and Materials Research (IFW Dresden), Helmholtzstrasse 20, 01069 Dresden, Germany.
Evgenia
E
Dmitrieva
Center of Spectroelectrochemistry, Leibniz Institute for Solid State and Materials Research (IFW Dresden), Helmholtzstrasse 20, 01069 Dresden, Germany.
Marco
M
Rosenkranz
TU Chemnitz, Institut für Chemie, Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany. holm.petzold@chemie.tu-chemnitz.de.
Marcus
M
Korb