Towards a Molecular Understanding of Cation-Anion Interactions-Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy, X-ray Photoelectron Spectroscopy and Theoretical Calculations
Towards a Molecular Understanding of Cation-Anion Interactions-Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy, X-ray Photoelectron Spectroscopy and Theoretical Calculations
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DOI：
10.1002/chem.201001032
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Steinrueck, Hans-Peter
中科院分区：
文献类型：
--
作者：
Cremer, Till;Kolbeck, Claudia;Steinrueck, Hans-Peter
含阴离子[C(8)C(1)Im](+)(1-甲基-3-辛基咪唑)(+)(Tf2N=三氟甲基磺酸盐，Tf2N=双(三氟甲基磺酰亚胺)，Pf(2)N=双(五氟乙磺酰亚胺)，Pf(2)N=双(五氟乙磺酰亚胺)，用X-射线光电子能谱、核磁共振和理论计算研究了FAP=tris-(pentafluoroethyl)trifluorophosphate)和两种[C(8)C(1)C(1)Im](+)(1，2-二甲基-3-辛基咪唑)离子液体及其阴离子[BR-和[Tf2N](-)。虽然H-1核磁共振谱被发现非常准确地探测到C-2位置上的氢与阴离子之间最强的氢键相互作用，但X.PS的比较研究首次提供了离子液体中阳离子-阴离子电荷转移现象作为离子液体阴离子的函数的直接实验证据。对于同一阴离子的[C(8)C(1)Im](+)和[C(8)C(1)C(1)Im](+)盐，这些电荷转移效应惊人地相似，结合理论计算得出结论：氢键和电荷转移相互独立地发生，但对于小而配位较强的阴离子，两者都更加明显，而在大而配位较弱的阴离子的情况下，氢键和电荷转移都大大减弱。
Ten [C(8)C(1)Im](+) (1-methyl-3-octylimidazolium)-based ionic liquids with anions Cl-, Br-, I-, [NO3](-), [BE4](-), [TfO](-), [PF6](-), [Tf2N](-), [Pf(2)N](-), and [FAP](-) (TfO=trifluoromethylsulfonate, Tf2N=bis(trifluoromethylsulfonyl)imide, Pf(2)N=bis(pentafluoroethylsulfonyl)imide, FAP=tris-(pentafluoroethyl)trifluorophosphate) and two [C(8)C(1)C(1)Im](+) (1,2-dimethyl-3-octylimidazolium)-based ionic liquids with anions Br- and [Tf2N](-) were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While H-1 NMR spectroscopy is found to probe very specifically the strongest hydrogen-bond interaction between the hydrogen attached to the C-2 position and the anion, a comparative X.PS study provides first direct experimental evidence for cation-anion charge-transfer phenomena in ionic liquids as a function of the ionic liquid's anion. These charge-transfer effects are found to be surprisingly similar for [C(8)C(1)Im](+) and [C(8)C(1)C(1)Im](+) salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions.