Thermal analysis and Raman spectra of different phases of the ionic liquid butyltrimethylammonium bis(trifluoromethylsulfonyl)imide.
The ionic liquid butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, [C(4)C(1)C(1)C(1)N][Tf(2)N], is a glass-forming liquid that exhibits partial crystallization depending on the cooling rate. Differential scanning calorimetry (DSC) indicates crystallization at T(c) = 227 K, melting at T(m) = 258 K, glass transition at T(g) ~ 191 K, and also cold crystallization at T(cc) ~ 219 K. Raman spectroscopy shows that the crystalline structure obtained by slow cooling is formed with [Tf(2)N](-) in cisoid conformation, whereas [Tf(2)N](-) in transoid conformation results from fast cooling. No preferred conformation of the butyl chain of the [C(4)C(1)C(1)C(1)N](+) cation is favored by slow or fast cooling of [C(4)C(1)C(1)C(1)N][Tf(2)N]. Low-frequency Raman spectroscopy shows that crystalline domains developing in the supercooled liquid result in a glacial state made of a mixture of crystallites and amorphous phase. However, these crystalline structures obtained by slow cooling or cold crystallization are not the same because anion-cation interactions promote local structures with distinct conformations of the [Tf(2)N](-) anion.
Laboratório de Espectroscopia Molecular, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05513-970 São Paulo, SP, Brazil.
Luiz F O
LF
Faria
Jivaldo R
JR
Matos
Mauro C C
MC
Ribeiro