Low-temperature heat capacities of 1-alkyl-3-methylimidazolium bis(oxalato)borate ionic liquids and the influence of anion structural characteristics on thermodynamic propertiesElectronic supplementary information (ESI) available: 1H, 13C and 11B NMR spectra and TG/DTG curves of [Bmim][BOB] and [Hmim][BOB] ILs. See DOI: 10.1039/c0cp01744b

• Main Authors: Yang, Miao, Zhao, Jun-Ning, Liu, Qing-Shan, Sun, Li-Xian, Yan, Pei-Fang, Tan, Zhi-Cheng, Welz-Biermann, Urs
• Format: Journal Article
• Language: English
• Published: 08.12.2010
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c0cp01744b

Two chelated orthoborate ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(oxalato)borate ([Bmim][BOB]) and 1-hexyl-3-methylimidazolium bis(oxalato)borate ([Hmim][BOB]), were prepared and characterized. Their thermodynamic properties were studied using adiabatic calorimetry and differential scanning calorimetry (DSC). The thermodynamic properties of the two ILs were evaluated and compared with each other, and then with those of other [Bmim] type ILs. The results clearly indicate that for a given cation (or anion) and at a certain temperature, the more atoms in the anion (or cation), the higher the heat capacity; the higher glass-transition temperatures of [BOB] type ILs than others are mainly caused by the higher symmetry of the orthoborate anion structure. It is suggested that a high content of strong electronegative atoms and C n or C nv ( n = 1,2,3,...,∞) point group symmetry in the anion are favorable for the design and synthesis of room temperature ILs with a wide liquid range. Thermodynamic properties studies suggest C n or C nv ( n = 1,2,...,∞) point group symmetry in ionic liquid anion favoring a wide liquid range.