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Issue 14, 2018
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Cobalt(II) liquid metal salts for high current density electrodeposition of cobalt

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Abstract

Cobalt(II)-containing ionic liquids were synthesized using N,N-dimethylformamide, N-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc), pyridine-N-oxide (py-O), 1,10-phenanthroline (phen), ethylenediamine (en) and dimethylimidazolidinone (DMI) as ligands. The weakly coordinating bis(trifluoromethylsulfonyl)imide (Tf2N) was used as a counter anion. Several compounds had a melting temperature below 100 °C, and the compound [Co(DMAc)6][Tf2N]2 was liquid at room temperature, with a viscosity of only 18 mPa s at 80 °C. Several compounds were recrystallized to give high quality single crystals and their crystal structures were determined. EXAFS measurements were performed on [Co(DMAc)6][Tf2N]2 at different temperatures and it was observed that the [Co(DMAc)6]2+ ion partially dissociated at higher temperatures, which explains the temperature-dependent color change (thermochromism). The electrochemical properties of the compounds with the lowest melting points were also investigated. Adherent, crack-free metallic cobalt layers could be electrodeposited from [Co(DMAc)6][Tf2N]2, [Co(DMI)6][Tf2N]2 and [Co(NMP)6][Tf2N]2. From the first two, black deposits consisting of micrometer-sized needles were obtained, whereas the latter resulted in a dull grey cobalt layer consisting of micrometer-sized cobalt spheres. The Co(III)/Co(II) redox couple was not found to occur in any compound with an O-donor ligand, but the Co(III)/Co(II) redox couple was found to be quasi-reversible for [Co(phen)3][Tf2N]2 dissolved in [BMP][Tf2N].

Graphical abstract: Cobalt(ii) liquid metal salts for high current density electrodeposition of cobalt

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Publication details

The article was received on 22 Jan 2018, accepted on 27 Feb 2018 and first published on 28 Feb 2018


Article type: Paper
DOI: 10.1039/C8DT00283E
Citation: Dalton Trans., 2018,47, 4975-4986
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    Cobalt(II) liquid metal salts for high current density electrodeposition of cobalt

    J. Sniekers, P. Geysens, T. Vander Hoogerstraete, L. Van Meervelt, J. Fransaer and K. Binnemans, Dalton Trans., 2018, 47, 4975
    DOI: 10.1039/C8DT00283E

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