File(s) under permanent embargo

Aluminium speciation in 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide/AlCl3 mixtures

journal contribution
posted on 23.03.2008, 00:00 authored by N Rocher, E Izgorodina, T Rüther, Maria ForsythMaria Forsyth, D MacFarlane, T Rodopoulos, M Horne, A Bond
Aluminium 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].

History

Journal

Chemistry - a European journal

Volume

15

Issue

14

Pagination

3435 - 3447

Publisher

Wiley - V C H Verlag GmbH & Co. KGaA

Location

Weinheim, Germany

ISSN

0947-6539

eISSN

1521-3765

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2009, Wiley-VCH Verlag GmbH&Co. KGaA