Aluminium Speciation in 1‐Butyl‐1‐Methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide/AlCl₃ Mixtures

Abstract

Electrodeposition of aluminium is possible from solutions of AlCl(3) dissolved in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (C(4)mpyrNTf(2)) ionic liquid. However, electrodeposition is dependant on the AlCl(3) concentration as it only occurs at concentrations >1.6 mol L(-1). At these relatively high AlCl(3) concentrations the C(4)mpyrNTf(2)/AlCl(3) mixtures exhibit biphasic behaviour. Notably, at 1.6 mol L(-1) AlCl(3), 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 C(4)mpyrNTf(2)/AlCl(3) system is described and implications of aluminium speciation in several C(4)mpyrNTf(2)/AlCl(3) mixtures, as deduced from Raman and (27)Al NMR spectroscopic data, are discussed. The (27)Al NMR spectra of the C(4)mpyrNTf(2)/AlCl(3) mixtures revealed the presence of both tetrahedrally and octahedrally coordinated aluminium species. Raman spectroscopy revealed that the level of uncoordinated NTf(2)(-) anions decreased with increasing AlCl(3) 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 [AlCl(3)(NTf(2))](-) or [AlCl(2)(NTf(2))(2)](-).

The Electrode/Ionic Liquid Interface: Electric Double Layer and Metal Electrodeposition

“…[136] In the ionic liquids composed of strongly coordinating anions such as N(Tf) 2 À , an anion coordination layer may be formed with the dissolved metal ions, and is regarded as the first solvation layer. [137] lanthanide ions such as La III , Eu III , and Yb III , [138] and Al III [139] and alkali-metal ions [140] are all coordinated by N(Tf) 2 À .…”

Chromium electrodeposition from [BMIm][BF4] ionic liquid

“…Deposition of pure metals and alloys of over 35 metals has been achieved from ILs. The mechanism of Al electroreduction and the nature of electroactive species in the ILs/AlCl 3 system are discussed in [9]. According to the data published by Forsyth et al [10], the film formation on the metal surfaces is not a simple chemical interaction between the components of the IL and substrate but may involve electrochemical processes.…”

Cobalt(II) Complexes of Nitrile‐Functionalized Ionic Liquids

“…Knowledge of the coordination chemistry of metal complexes of ionic liquids is important for applications of ionic liquids to electrodeposition of metals, because the coordination chemistry in ionic liquids often differs from that in aqueous solution and because not all the metal complexes present in an ionic-liquid medium are electroactive. [10] Here we report on a series of nitrile-functionalized pyrrolidinium ionic liquids and on the electron-donor abilities of these solvents in the dissolution process of cobalt(II) bis(trifluoromethylsulfonyl)imide ("bistriflimide") salts.…”