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

Abstract

Ten [C(8)C(1)Im](+) (1-methyl-3-octylimidazolium)-based ionic liquids with anions Cl(-), Br(-), I(-), [NO(3)](-), [BF(4)](-), [TfO](-), [PF(6)](-), [Tf(2)N](-), [Pf(2)N](-), and [FAP](-) (TfO=trifluoromethylsulfonate, Tf(2)N=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 [Tf(2)N](-) were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While (1)H 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 XPS 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.

Palladium–poly(ionic liquid) membranes for permselective sonochemical flow catalysis

“…S3. The N(1s) binding envelope of the quaternised films could be fitted to a main nitrogen environment at 401.9 ± 0.1 eV corresponding to two equivalent nitrogen centres in positively charged imidazolium rings [39,51,52], Fig. 3 and Scheme 1.…”

X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3

“…Using X-ray photoelectron spectroscopy [ok? ], it has been demonstrated that the ionic liquid anion can affect q i on the cation (Cremer et al, 2010). In addition, EXAFS spectroscopy with hard X-rays has been used to study structure in ionic liquids (Hartley et al, 2014, Migliorati et al, 2015.…”

Surface Science and Model Catalysis with Ionic Liquid‐Modified Materials

“…Recent work by several groups [30][31][32][33][34][35][36][37][38][39][40][41][42][43] including those of the authors [44][45][46][47][48][49][50][51][52][53][54][55][56][57] shows that a rigorous surface science approach can indeed be applied to IL surfaces and interfaces. There are mainly two aspects, which make such studies possible: First, the vapor pressure of many aprotic ILs is suffi ciently low so that their surfaces can be straightforwardly studied under ultrahigh vacuum (UHV) conditions.…”