X-Ray Photoelectron Spectroscopy (XPS) is a well stablished technique to study elemental composition as well as physical and chemcial properties of ionic liquids (ILs). XPS studies of antimony compounds are mainly focused on antimony oxides and halides rather than on SbF6-containing ILs. First reports from early 1970s showed uncertain binding energy (BE) values for antimony photoemission peaks, probably due to limitations imposed by equipment and data processing at that time. Herein, we present a XPS study of 1-alkyl-3-methylimidazolium hexafluoroantimonate ILs of general formula [CnC1Im][SbF6], where n = 4,8 and 12. XP spectra were recorded using a Kratos Axis Ultra Spectrometer with a monochromated Al Ka source (1486.6 eV) and charge-referencing of BE for all elements was achieved using 285.0 eV for Caliphatic1s (when n = 8 and 12) or 402.2 eV for N1s (for n = 4). Using this model, the measured BE values for F 1s (686.2 eV), N 1s (402.2 eV) and C 1s components (C2 = 287.8 eV; C4-C5 = 287.0 eV; C6-C7 = 286.6 eV, Caliph = 285.0 eV) were reproducible within the experimental error of ± 0.1 eV. Sb 3d peak was fitted taking into account the 3d3/2/3d5/2 spin orbit coupling splitting of 9.3 ± 0.1 eV.Thus, Sb (V) 3d3/2 component was observed at 542.5 eV while Sb (V) 3d5/2 at 533.1 eV. However, an interesting mixed oxidation-state system for Sb peak was noticed for these ILs. Besides the main assigned Sb (V) peaks, it was also possible to identify Sb 3d3/2 and Sb 3d5/2 components for antimony (III) at lower BE values, due to photoreduction of Sb (V) to Sb (III) caused by long exposure to X-ray, a phenomenon previously described for Cs2SbCl5. Applying the same fitting model used for Sb (V) components, it was possible to identify BE values of 541.0 eV and 531.7 eV for Sb (III) 3d3/2 and Sb (III) 3d5/2, respectively. High resolution scan spectra of Sb 3d peak for all [CnC1Im][SbF6] are showed in Figure 1. The good applicability of our fitting model for Sb 3d peak can be recognized by measuring the level separation of [Sb (V) 3d3/2 – Sb (III) 3d3/2] peaks as well as [Sb (V) 3d5/2 – Sb (III) 3d5/2] peaks, which remained constant at 1.40 ± 0.1 eV.

Study of the stability of 1-alkyl-3-methylimidazolium hexafluoroantimonate ionic liquids using X-ray photoelectron spectroscopy

250th National Meeting (2015)

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