Cobalt(ii) liquid metal salts for high current density electrodeposition of cobalt. Issue 14 (20th March 2018)

• Record Type: Journal Article
• Authors: Sniekers, Jeroen; Geysens, Pieter; Vander Hoogerstraete, Tom; Van Meervelt, Luc; Fransaer, Jan; Binnemans, Koen
• Is Part Of: Dalton transactions. Volume 47:Issue 14(2018)
• Page Start: 4975
• Page End: 4986
• Publication Date: 2018-03-20
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c8dt00283e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Cobalt-containing liquid metal salts were synthesized and characterized. Reversible thermochromism was observed and the electrodeposition of cobalt layers with different morphologies was investigated. 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 (Tf2 N − ) was used as a counter anion. Several compounds had a melting temperature below 100 °C, and the compound [Co(DMAc)6 ][Tf2 N]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 ][Tf2 N]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 ][Tf2 N]2, [Co(DMI)6 ][Tf2 N]2 and [Co(NMP)6 ][Tf2 N]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 ][Tf2 N]2 dissolved in [BMP][Tf2 N].