Fluoride Ion-Encapsulated Germoxane Cages Modified with Organosiloxane Chains as Anionic Components of Ionic Liquids

Abstract

Herein, we report the preparation of a new class of inorganic−organic hybrid ionic liquids by modification of a doublefour-ring (D4R)-type germoxane (Ge−O−Ge) compound, containing a fluoride ion inside and a tetraethylammonium cation outside, with organosiloxane chains. D4R-type inorganic compounds are attractive as anionic components of ionic liquids because of their ability to encapsulate a fluoride ion inside the cage and allow various functional groups to be linked at the cage corners. The crystalline D4R-type germoxanes with corner Ge−OH groups were successfully converted to clear liquids by modification with dimethylvinylsilyl groups, followed by hydrosilylation with flexible oligosiloxanes (HSi(OSiMe 3 ) n Me 3−n , n = 1−3). The resulting products showed liquid behaviors below 0 °C and were stable against thermal decomposition up to ∼200 °C. Additionally, they had high affinities for both hydrophilic and hydrophobic substances, attributable to the organosiloxane chains surrounding the ionic cage. Furthermore, the differences between the D4R-type germoxane and D4R-type siloxane were investigated using density functional theory calculations. The symmetry of the optimized structure and its electrostatic nature indicated that D4R-type germoxane is advantageous for the creation of ionic liquids.

Integrated Extrinsic and Intrinsic Self‐Healing of Polysiloxane Materials by Cleavable Molecular Cages Encapsulating Fluoride Ions

“…The solid‐state 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of PDMS‐GeD4R is shown in Figure 1c . The absence of the signal for the terminal SiMe 2 H groups of PDMS (≈−7 ppm) and the appearance of the signals for (SiO) Si Me 2 CH 2 – ( C : δ = 8.6 ppm) and (GeO) Si Me 2 CH 2 – ( D : δ = 16.3 ppm) [ 16 ] indicated that hydrosilylation reaction proceeded. Signals for the residual vinylsilyl groups [(GeO) Si Me 2 CH=CH 2 ] ( B : δ = 3.1 ppm) and PDMS main chains [ Si Me 2 (OSi) 2 ] ( A : δ = −21.9 ppm) were also observed.…”

“…The solid‐state 19 F MAS NMR spectrum of PDMS‐GeD4R (Figure 1d ) showed a signal at δ = −14.5 ppm, which was assigned to F − inside the germoxane cage. [ 12 , 15 , 16 ] Other signals at δ = −131.2 and −163.9 ppm were assignable to the Si–F and Ge–F species, respectively, based on the 19 F NMR spectra of F − ‐treated siloxane and germoxane compounds (for details, see Figures S4–S6 , Supporting Information). These species indicated that F − was partially released from the cage during the synthesis of PDMS‐GeD4R .…”

“…[ 8c ] Such a difference can be attributed to the higher thermal stability of the F − ‐encapsulating cage structures and Si–F bonds over silanolates. We have previously synthesized F − ‐encapsulating cage germoxane‐based cross‐linked networks [ 16a ] and ionic liquids [ 16b ] and investigated their thermal stability, confirming that they were thermally stable without decomposition up to ≈200 °C. The thermal and chemical stability of Si–F compounds such as SiF 4 was also revealed by computational simulations.…”

“…[ 15 ] This allowed post‐chemical modification through hydrosilylation without deteriorating the cage structure. [ 15 , 16 ] These features of F – ‐encapsulating germoxane cages guarantee their uniform molecular‐level incorporation into silicone networks.…”

The Potential Role of Ionic Liquid as a Multifunctional Dental Biomaterial

“…Hayashi et al recently explored a technique enabling ILs to formulate fluoridated toothpaste. They reported preparing a new class of hybrid ILs, called "fluoride ion-encapsulated germoxane cages", containing a fluoride ion inside [133].…”