The thermal decomposition of Samarium-Thiocyanate-Based ionic liquids

New lanthanide containing ionic liquids (ILs) based on thiocyanate complexes of the type [BMIM](x-3)[Ln (NCS)(x)(H2O)(y)] (BMIM = 1-Butyl-3-Methylimidazolium; x = 6,7,8; y = 0-2, x + y < 10; Ln = Y, La-Yb) have been reported in recent studies. These complexes are highly efficient in dissolving lanthanide complexes within ILs. The present work includes a thermal decomposition study of the anhydrous ionic liquids of this type with Samarium cation as the lanthanide. The thermal decomposition of [BMIM][NCS], [BMIM](3)[Sm(NCS)(6)], [BMIM](4)[Sm(NCS)(7)] and [BMIM](3)[Sm(NCS)(8)] was investigated by employing a combination of thermo-gravimetric analysis (TGA), and temperature programmed desorption (TPD) coupled with mass spectrometry. The decomposition temperature of the samarium-containing ILs were found to be higher than that measured for [BMIM][NCS], suggesting stabilization of the ILs by complexation to the samarium cation. Thermal gravimetric analysis of [BMIM](x-3)[Sm(NCS)(x)] confirms that the thermal decomposition occurs in a stepwise fashion to give Sm(NCS)(3) via a [BMIM](3)[Sm(NCS)(6)] intermediate, whereby [BMIM][NCS] units are decomposed to give gaseous products. Additional experimental evidence obtained with TPD-MS supporting this decomposition route and reveal that each [BMIM][NCS] unit decomposes by the rapid nucleophilic attack of the thiocyanate anion at the C-N bond of the methyl- and butyl- imidazole groups, and their proposed reaction mechanism are introduced here. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Recent studies have reported new lanthanide containing ionic liquids (ILs) that are highly efficient in dissolving lanthanide complexes within ILs. Thermal decomposition studies have shown that the samarium-containing ILs have higher decomposition temperatures than conventional ILs, indicating stabilization by complexation to the samarium cation. The decomposition pathway and reaction mechanism involve rapid nucleophilic attacks on the C-N bond of the imidazole groups, as revealed by experimental evidence using TPD-MS.