Synthesis, vibrational, thermal, topological, electronic, electrochemical stability and DFT studies of new DABCO based ionic liquids

The design of new ILs with different anions could provide interesting physico-chemical properties and for these reasons, the knowledge about the synthesis, the thermal, vibrational, topological, electronic, electrochemical properties and interaction between the selected cation-anion in these ILs are important subjects. Therefore, the understanding about these properties of these compounds is an important subject of study. In this work, we studied three ionic liquids based on the 1-decyl-1,4-diazabicyclo[2.2.2]octane, DABCO-cation, where the corresponding anions were [Br]-, [PF6]-, and [N(SO₂CF₃)₂]-. The syntheses of these bicyclic DABCO ionic liquids are based on an alkylation reaction of 1,4-diazabicyclo[2.2.2] octane and 1-bromodecanefollowed by anion exchange. The obtained ILs are characterized by 1H, 13C, 19F and 31P-NMR spectroscopy. Vibrational spectroscopy studies are conducted by infrared (FTIR/ATR) and Raman spectroscopy in the wavenumber range 600–4000 cm-1 and 45–3500 cm-1, respectively. Furthermore, the thermal stabilities were investigated using the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods. Results indicate that the thermal stability follow the order [C10DABCO][Br]<[C10DABCO][PF6]<[C10DABCO][N(SO₂CF₃)₂]. Additionally, the structural parameters, electrostatic potential (ESP) maps, interaction energies, non-covalent interaction (NCI), atoms in molecule (AIM) analysis, natural bond orbital (NBO), frontier molecular orbital (FMO) analysis and Electrochemical window (ECW) are studied and analyzed by means of DFT calculations at the M06–2X-GD3/AUG–cc–pVDZ level of theory.