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Issue 14, 2017
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Tuneable reversible redox of cobalt(III) carbazole complexes

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Four tridentate carbazole-based ligands, HLtBu/H {3,6-di(tert-butyl)-1,8-bis[5-(3-benzyl-1,2,3-triazole)]-9H-carbazole}, HLtBu/tBu {3,6-di(tert-butyl)-1,8-bis[5-(3-(4-tert-butyl)benzyl-1,2,3-triazole)]-9H-carbazole}, HLH/H {1,8-bis[5-(3-benzyl-1,2,3-triazole)]-9H-carbazole} and HLH/tBu {1,8-bis[5-(3-(4-tert-butyl)benzyl-1,2,3-triazole)]-9H-carbazole}, were prepared and complexed with cobalt(II) tetrafluoroborate. In situ air oxidation resulted in cobalt(III) complexes 1–4 with the general formula [CoIII(L)2]BF4·xH2O (1: L = LtBu/H, x = 2; 2: L = LtBu/tBu, x = 1; 3: L = LH/H, x = 0.5; 4: L = LH/tBu, x = 2). X-ray structural characterisation confirmed that the four complexes are isostructural, with two orthogonally coordinated deprotonated tridentate ligands providing an octahedral N6-donor set to the cobalt(III) ion. 1H NMR studies show that this structure is maintained in CDCl3 and DMSO-d6 solution. Cyclic voltammetry on 1–4 in MeCN showed that all of the complexes exhibit two reversible, one-electron oxidation processes (probably due to ligand oxidations), and an irreversible or quasi-reversible reduction process (probably due to reduction of Co(III) to Co(II)). As expected, the oxidations move 120–140 mV to lower potentials on adding tert-butyl substituents to the 3 and 6 positions of the carbazole rings, and unsurprisingly the potentials are far less sensitive to the nature of the benzyl ring substituents.

Graphical abstract: Tuneable reversible redox of cobalt(iii) carbazole complexes

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Publication details

The article was received on 25 Jan 2017, accepted on 02 Mar 2017 and first published on 07 Mar 2017

Article type: Paper
DOI: 10.1039/C7DT00295E
Dalton Trans., 2017,46, 4696-4710

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    Tuneable reversible redox of cobalt(III) carbazole complexes

    M. S. Bennington, H. L. C. Feltham, Z. J. Buxton, N. G. White and S. Brooker, Dalton Trans., 2017, 46, 4696
    DOI: 10.1039/C7DT00295E

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