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Aluminium speciation in 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide/AlCl3 mixtures
journal contribution
posted on 2008-03-23, 00:00 authored by N Rocher, E Izgorodina, T Rüther, Maria ForsythMaria Forsyth, D MacFarlane, T Rodopoulos, M Horne, A BondAluminium speciation: Aluminium speciation in NTf2 ionic liquids has a strong influence on its electrodeposition from the liquid mixture. This work probed the nature of these species and proposes that the electroactive species involved are either [AlCl3(NTf2)]− or [AlCl2(NTf2)2]− (e.g., see figure).
Electrodeposition of aluminium is possible from solutions of AlCl3 dissolved in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (C4mpyrNTf2) ionic liquid. However, electrodeposition is dependant on the AlCl3 concentration as it only occurs at concentrations >1.6 mol L−1. At these relatively high AlCl3 concentrations the C4mpyrNTf2/AlCl3 mixtures exhibit biphasic behaviour. Notably, at 1.6 mol L−1 AlCl3, aluminium can only be electrodeposited from the upper phase. Conversely, we found that at 3.3 mol L−1 aluminium electrodeposition can only occur from the lower phase. The complex chemistry of the C4mpyrNTf2/AlCl3 system is described and implications of aluminium speciation in several C4mpyrNTf2/AlCl3 mixtures, as deduced from Raman and 27Al NMR spectroscopic data, are discussed. The 27Al NMR spectra of the C4mpyrNTf2/AlCl3 mixtures revealed the presence of both tetrahedrally and octahedrally coordinated aluminium species. Raman spectroscopy revealed that the level of uncoordinated NTf2− anions decreased with increasing AlCl3 concentration. Quantum chemical calculations using density functional and ab initio theory were employed to identify plausible aluminium-containing species and to calculate their vibrational frequencies, which in turn assisted the assignment of the observed Raman bands. The data indicate that the electroactive species involved are likely to be either [AlCl3(NTf2)]− or [AlCl2(NTf2)2]−.
Electrodeposition of aluminium is possible from solutions of AlCl3 dissolved in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (C4mpyrNTf2) ionic liquid. However, electrodeposition is dependant on the AlCl3 concentration as it only occurs at concentrations >1.6 mol L−1. At these relatively high AlCl3 concentrations the C4mpyrNTf2/AlCl3 mixtures exhibit biphasic behaviour. Notably, at 1.6 mol L−1 AlCl3, aluminium can only be electrodeposited from the upper phase. Conversely, we found that at 3.3 mol L−1 aluminium electrodeposition can only occur from the lower phase. The complex chemistry of the C4mpyrNTf2/AlCl3 system is described and implications of aluminium speciation in several C4mpyrNTf2/AlCl3 mixtures, as deduced from Raman and 27Al NMR spectroscopic data, are discussed. The 27Al NMR spectra of the C4mpyrNTf2/AlCl3 mixtures revealed the presence of both tetrahedrally and octahedrally coordinated aluminium species. Raman spectroscopy revealed that the level of uncoordinated NTf2− anions decreased with increasing AlCl3 concentration. Quantum chemical calculations using density functional and ab initio theory were employed to identify plausible aluminium-containing species and to calculate their vibrational frequencies, which in turn assisted the assignment of the observed Raman bands. The data indicate that the electroactive species involved are likely to be either [AlCl3(NTf2)]− or [AlCl2(NTf2)2]−.
History
Journal
Chemistry - a European journalVolume
15Issue
14Pagination
3435 - 3447Publisher
Wiley - V C H Verlag GmbH & Co. KGaALocation
Weinheim, GermanyPublisher DOI
ISSN
0947-6539eISSN
1521-3765Language
engPublication classification
C1.1 Refereed article in a scholarly journalCopyright notice
2009, Wiley-VCH Verlag GmbH&Co. KGaAUsage metrics
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ab initio calculationsaluminumelectrodepositionionic liquidsNMR spectroscopyRaman spectroscopyScience & TechnologyPhysical SciencesChemistry, MultidisciplinaryChemistryCHLOROALUMINATE IONIC LIQUIDSNUCLEAR-MAGNETIC-RESONANCEMOLTEN-SALTCOMPLEX-COMPOUNDSTEMPERATURECHLORIDESYSTEMSWATERBIS(TRIFLUOROMETHANESULFONYL)IMIDE
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