Synthesis and Structures of Novel Molecular Ionic Compounds Based on Encapsulation of Anions and Cations

El Aziz, Youssef; Taylor, Peter G.; Bassindale, Alan R.; Coles, Simon J. and Pitak, Mateusz B. (2016). Synthesis and Structures of Novel Molecular Ionic Compounds Based on Encapsulation of Anions and Cations. Organometallics, 35(24) pp. 4004–4013.



The novel coordinate compounds T8[(CH2)n-EWG]8F-18-crown-6-M+ were prepared by reaction of EWG-(CH2)n-Si(OEt)3 (where n = 1−3 and the electron-withdrawing group, EWG, contains an Si−C(sp3) bond) with an 18-crown-6-M+F complex (where M+ is K+, Cs+, and Rb+) in the presence of a limited amount of water. The EWG facilitates the formation and encapsulation of the fluoride anion in a silsesquioxane cage. The reaction takes place by complexing an alkali metal in the crown ether, catalyzing silsesquioxane cage formation, and concomitant encapsulation of a fluoride ion within the final T8 cage. The reaction is simple and takes place in a single step with excellent yields of 81−95%. These novel materials have been studied by 19F and 29Si NMR spectroscopy and X-ray crystallography as well as by MALDI-TOF and ESI mass spectrometry. The T8[(CH2)n-EWG]8F-18-crown-6-M+ compounds can be also synthesized by a facile reaction of 18-crown-6-M+F with the corresponding T8[(CH2)n-EWG]8 cage in nearly quantitative yield. Surprisingly, the single-crystal X-ray diffraction analysis has revealed the presence of 1D and 3D polymeric complexes of T8[(CH2)n-EWG]8F-18-crown-6-M+. To the best of our knowledge, this represents the first dual-encapsulation host−octasilsesquioxane system. The results from thermostability experiments monitored by 19F NMR and 1H NMR and DSC suggest that compound T8[CH2CH2(CF2)3CF3]8F-18-crown-6-K+ is a potential ionic liquid (IL).

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