A combined experimental and theoretical study on the structures, interactions and volumetric properties of guanidinium-based ionic liquid mixtures. Issue 32 (1st August 2019)

• Record Type: Journal Article
• Authors: Lu, Xiaoxing; Xie, Hujun; Lei, Qunfang; Fang, Wenjun
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 32(2019)
• Page Start: 17720
• Page End: 17728
• Publication Date: 2019-08-01
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp02999k
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Mixing of ILs leads to changes of interactions and different structures. Abstract : Mixtures of ionic liquids (ILs) have shown their potential in both physical and chemical processes, regarded as alternatives to common ILs. In this work, four guanidinium-based ILs, 2-ethyl-1, 1, 3, 3-tetramethylguanidinium ethyl sulfate ([TMG(C2 )][C2 OSO3 ]) and bis(trifluoromethylsulfonyl)imide ([TMG(C2 )][NTf2 ]), and 2, 2-diethyl-1, 1, 3, 3-tetramethylguanidinium ethyl sulfate ([TMG(C2 )2 ][C2 OSO3 ]) and bis(trifluoromethylsulfonyl)imide ([TMG(C2 )2 ][NTf2 ]), are employed to investigate the structures, interactions and properties of four systems of IL–IL binary mixtures, including [TMG(C2 )][C2 OSO3 ] x [NTf2 ]1− x, [TMG(C2 )] x [TMG(C2 )2 ]1− x [C2 OSO3 ], [TMG(C2 )] x [TMG(C2 )2 ]1− x [NTf2 ] and [TMG(C2 )2 ][NTf2 ] x [C2 OSO3 ]1− x . Combining experiments with theory, the relationships among H-bond interactions, structures and volumetric properties have been revealed. 1 H NMR characterizations show the changes of H-bond interactions in the IL–IL mixtures in relation to composition, and DFT calculations reveal significant cation–anion interactions through the active hydrogen atom (N + –H) and the methyl groups in the cations with the anions in the manner of H⋯O and H⋯F. The ethyl group in the [C2 OSO3 ] − anion hardly forms interactions with other components. The size effect of the calculated system has been evaluated for the IL–IL clusters with 2, 4 and 8 ions. Different structures due to variation of cationic and anionic species have remarkable influence on the volumetric properties of the IL–IL mixtures. Negative excess molar volume ( V Em) is found in [TMG(C2 )] x [TMG(C2 )2 ]1− x [C2 OSO3 ], and it is caused by the close packing of ions. Positive V Em values indicate that interaction loss occurs in the other three systems, where a linear arrangement or square packing of ions with low space utilization is found.