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

Abstract

The novel coordinate compounds T 8 [(CH 2 ) n -EWG] 8 F − -18-crown-6-M + were prepared by reaction of EWG-(CH 2 ) n -Si(OEt) 3 (where n = 1−3 and the electron-withdrawing group, EWG, contains an Si−C(sp 3 ) 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 T 8 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 19 F and 29 Si NMR spectroscopy and X-ray crystallography as well as by MALDI-TOF and ESI mass spectrometry. The T 8 [(CH 2 ) n -EWG] 8 F − -18-crown-6-M + compounds can be also synthesized by a facile reaction of 18-crown-6-M + F − with the corresponding T 8 [(CH 2 ) 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 T 8 [(CH 2 ) n -EWG] 8 F − -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 19 F NMR and 1 H NMR and DSC suggest that compound T 8 [CH 2 CH 2 (CF 2 ) 3 CF 3 ] 8 F − -18-crown-6-K + is a potential ionic liquid (IL).

Self-assembly of fluoride-encapsulated polyhedral oligomeric silsesquioxane (POSS) nanocrystals

“…5, the 1D SAXS and WAXS profiles are quite complex certainly for the TBAF and crown compounds, showing many peaks in all cases. The high number of peaks in the WAXS profiles usually indicates a complex unit cell and for these compounds, it is reasonable to assume that they all have triclinic unit cells, as reported in our previous single crystal X-ray work 8,10,11 for TBAF and crown compounds where single crystals could be obtained. For POSS without F − ion encapsulation compounds, triclinic crystalline unit cells have also been reported 17 from single crystal analysis for these compounds.…”

“…10 The corresponding metal/ crown ether compounds were prepared in a similar fashion using the metal fluoride salt, the crown ether and the appropriate perfluoroalkyltrialkoxysilane. 11 The perfluoroalkyl POSS compounds without fluoride entrapment were synthesized according to Mabry et al 17 All compounds obtained from the synthesis were white crystalline solids at room temperature.…”

“…-crown ether-M + or T 8 ijEWG-(CH 2 )n] 8 F TBA + . 10,11 TBAFC 6 . TBAFC 8 and TBAFC 10 ; similarly, compounds prepared with 18-crown-6-K + and the same fluorinated alkyl arms are denoted as CrownC 3 , CrownC 6 , CrownC 8 and CrownC 10 ; POSS cages T 8 without any F − ion encapsulation, but with the same fluorinated alkyl arms, are denoted as C 3 , C 6 and C 8 herein.…”

“…This is then followed by a second decomposition process of the weight loss of the fluorinated alkyl chain arms. 11 For the TBAF compounds, increasing the fluorinated alkyl chain arm length gives increased values of T d . Hence, here the increased arm length, and assumed packing, gives greater stability of the compounds.…”

“…1). 10,11 In the unit cell, each cage-encapsulated fluoride ion is associated with the counter ion where the packing depends upon the most efficient space filling arrangement of the cation and anion depending upon the nature of the arms attached to the cage.…”