Redox properties and electron transfer in a triarylamine-substituted HS-Co2+/LS-Co3+ redox couple. Issue 8 (7th February 2017)

• Record Type: Journal Article
• Authors: Schnaubelt, Linda; Petzold, Holm; Speck, J. Matthäus; Dmitrieva, Evgenia; Rosenkranz, Marco; Korb, Marcus
• Is Part Of: Dalton transactions. Volume 46:Issue 8(2017)
• Page Start: 2690
• Page End: 2698
• Publication Date: 2017-02-07
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt04748c
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The redox and electron transfer properties of a triarylamine decorated HS-Co 2+ /LS-Co 3+ redox couple were investigated by coupled EPR/UV-vis-NIR spectroelectrochemistry and 1 H NMR spectroscopy. Abstract : A new tridentate phenanthroline-pyridyl-based ligand1 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 [Co 2+ (1 )2 ](ClO4 /BF4 )2 was prepared and the order of the oxidation steps was analysed by cyclic voltammetry and EPR/UV-vis-NIR spectroelectrochemistry. Oxidation of [Co 2+ (1 )2 ] 2+ to [Co 3+ (1 + )2 ] 5+ proceeds in two steps. The first step is the Co 2+/3+ centred oxidation to [Co 3+ (1 )2 ] 3+ ( E °′(M 2+/3+ ) = 284 mV vs . Fc/Fc + ) followed by oxidation of the Tara 0/+ centres ( E °′(Tara) = 531 mV). Both kinds of oxidation processes were independently investigated in the analogous complexes [Zn(1 )2 ](ClO4 )2 and [Co(2 )2 ](BF4 )2 allowing 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 [Co 2+/3+ (1 )2 ] 2+/3+ couple. The electron transfer by self-exchange in [Co 2+/3+ (1 )2 ] 2+/3+ was further investigated by variable temperature (VT) 1 H NMR spectroscopy. In addition, the resonances found in the paramagnetic proton NMR spectra were assigned by using COSY, T 1 and 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 Fe 2+ species [Fe(1 )2 ](ClO4 )2 is a spincrossover system. The SCO was analysed in solution by VT 1 H NMR and VT/vis spectroscopy.