Laboratório de Espectroscopia Molecular, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05513-970 São Paulo, SP, Brazil.
J Phys Chem B. 2012 Aug 2;116(30):9238-45. doi: 10.1021/jp3051824. Epub 2012 Jul 12.
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.
离子液体丁基三甲基铵双（三氟甲烷磺酰基）亚胺，[C(4)C(1)C(1)C(1)N][Tf(2)N]，是一种形成玻璃的液体，其结晶程度取决于冷却速率。差示扫描量热法（DSC）表明在 T(c) = 227 K 处结晶，在 T(m) = 258 K 处熔融，在 T(g)191 K 处玻璃化转变，在 T(cc)219 K 处还发生冷结晶。拉曼光谱表明，缓慢冷却得到的结晶结构中Tf(2)N呈顺式构象，而快速冷却得到的结晶结构中Tf(2)N呈反式构象。无论是缓慢冷却还是快速冷却，[C(4)C(1)C(1)C(1)N][Tf(2)N]中的丁基链均没有优先的构象。低频拉曼光谱表明，在过冷液体中形成的结晶畴导致形成由结晶相和非晶相组成的冰态。然而，由于阴离子-阳离子相互作用促进了具有独特Tf(2)N阴离子构象的局部结构，因此缓慢冷却或冷结晶得到的这些结晶结构并不相同。
