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Speciation of Aluminium in Mixtures of the Ionic Liquids [C 3 mpip][NTf 2 ] and [C 4 mpyr][NTf 2 ] with AlCl 3 : An Electrochemical and NMR Spectroscopy Study
Author(s) -
Rodopoulos Theo,
Smith Leanne,
Horne Michael D.,
Rüther Thomas
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902753
Subject(s) - aluminium , ionic liquid , chemistry , amide , dissolution , inorganic chemistry , ionic bonding , aluminium chloride , analytical chemistry (journal) , ion , organic chemistry , catalysis
This paper reports on the electrodeposition of aluminium on several substrates from the air‐ and water‐stable ionic liquids 1‐propyl‐1‐methylpiperidinium bis(trifluoromethylsulfonyl)amide ([C 3 mpip][NTf 2 ]) and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([C 4 mpyr][NTf 2 ]), which contain anhydrous AlCl 3 . At an AlCl 3 concentration of 0.75 molal, no evidence for aluminium electrodeposition was observed in either system at room temperature. However, aluminium electrodeposition becomes feasible upon heating the samples to 80 °C. Aluminium electrodeposition from bis(trifluoromethylsulfonyl)amide‐based ionic liquids that contain AlCl 3 has previously been shown to be very dependent upon the AlCl 3 concentration and has not been demonstrated at AlCl 3 concentrations below 1.13 molal. The dissolution of AlCl 3 in [C 3 mpip][NTf 2 ] and [C 4 mpyr][NTf 2 ] was studied by variable‐temperature 27 Al NMR spectroscopy to gain insights on the electroactive species responsible for aluminium electrodeposition. A similar change in the aluminium speciation with temperature was observed in both ionic liquids, thereby indicating that the chemistry was similar in both. The electrodeposition of aluminium was shown to coincide with the formation of an asymmetric four‐coordinate aluminium‐containing species with an 27 Al chemical shift of δ =94 and 92 ppm in the [C 3 mpip][NTf 2 ]–AlCl 3 and [C 4 mpyr][NTf 2 ]–AlCl 3 systems, respectively. It was concluded that the aluminium‐containing species that give rise to these resonances corresponds to the electroactive species and was assigned to [AlCl 3 (NTf 2 )] − .