STRUCTURE AND INTERACTIONS OF DICATIONIC IMIDAZOLIUM IONIC LIQUIDS

VASILEIOS DRACOPOULOS, ICE-HT, FORTH, Patras, Greece
Anastasia-Maria Moschovi, Ice-ht, Forth, Patras, Greece
Antonis Syrigos, Ice-ht, Forth, Patras, Greece
Theodora Romiou, Ice-ht, Forth, Patras, Greece
Maria Daletou, Ice-ht, Forth, Patras, Greece
Theophilos Ioannides, Ice-ht, Forth, Patras, Greece
Georgia Tsolou, Mechanical Engineering, Technological Educational Institute, Patras, Greece
Alexandros Kalarakis, Mechanical Engineering, Technological Educational Institute, Patras, Greece

Present work focuses on the investigation of the local structure and interactions of either side M(CnH2n+1Im)2(NTf)2 (n=0-12) and/or linker CnH2n(MIm)2(NTf)2 (n=1-12) alkyl substituted imidazolium dicationic ionic liquids (DILs) through experimental and theoretical techniques (FTIR/ATR, Raman, DSC, molecular simulation). Results derived from this study were compared against corresponding data from protic monocationic (p-MIL) and/or aprotic (a-MIL) ILs and prove that the existence of two imidazole cations at one methylene distance has a tremendous effect on the local structure. While in protic DILs hydrogen bonding between anion and cation (N-H∙∙∙O) is stronger compared to p-MILS, in aprotic DILs the HB behaviour is more complicated since no certain shift is observed in C-H stretching modes but a change in their FWHM. Furthermore, the anion conformation is changed to even more populated cis structures compared to aprotic MILs. This is probably reflected to glass transition temperatures where, in contrast to the corresponding MILs, a decrease is occurred for up to hexyl side substituted DILs. All these findings are correlated to the induced coulombic field of the two imidazole molecules in the di-cation.
In the case of alkyl substituted DILs used as linkers, the FTIR spectra shows that as the alkyl chain length exceeds a critical value the overall spectral characteristics are similar to that of corresponding monocationic (aPILs). These preliminary results seem to support the fact that the distance between the two cations increases as the alkyl chain length increases and are consistent with experimental data collected by x-ray scattering measurements [1]. Finally, this spectral behaviour indicates that the local interactions in dicationic ones are presumably close to that of aprotic MILs.
REFERENCES
[1] S.Li et al, J.Phys.Chem. C 117, 18251 (2013)