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Issue 23, 2018
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Cobalt complexes with redox-active anthraquinone-type ligands

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Three anthraquinone-type multidentate ligands, HL1–3 (HL = 2-R-1H-anthra[1,2-d]imidazole-6,11-dione; HL1: R = (2-pyridyl), HL2; R = (4,6-dimethyl-2-pyridyl), HL3; R = (6-methoxy-2-pyridyl)), were prepared, and their complexation behaviour was investigated. Three bis-chelate cobalt complexes with the formula [CoII(L1–3)2n(solv.) (1, 2, and 3 for HL1, HL2, and HL3, respectively), in which the ligands adopted tridentate binding modes, were synthesized and structurally characterized by single-crystal X-ray analyses. Electrochemical studies of 1–3 in CH2Cl2 reveal three reversible redox waves, assigned to ligand and cobalt-centred processes. Additional complexes were obtained in which HL1 adopted a bidentate binding mode, stabilising the mono-chelate [CoII(HL1)(NO3)2(DMF)2] (4) species and tris-chelate [CoIII(L1)3] (5) complex in which the cobalt ion was in its 3+ state. The electrochemical properties of complex 5 were investigated in DMF, and the Co(II)/Co(III) redox couple was found to be negatively shifted compared to that of complex 1, while the ligand-based processes became irreversible. Tridentate chelation is found to stabilise the anthraquinone ligands and unlocks their redox multi-stability.

Graphical abstract: Cobalt complexes with redox-active anthraquinone-type ligands

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Supplementary files

Article information

12 Feb 2018
14 May 2018
First published
31 May 2018

Dalton Trans., 2018,47, 7804-7811
Article type

Cobalt complexes with redox-active anthraquinone-type ligands

T. Shiga, R. Kumamaru, G. N. Newton and H. Oshio, Dalton Trans., 2018, 47, 7804
DOI: 10.1039/C8DT00586A

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