02348nas a2200169   4500008004100000245010600041210006900147260000800216300001600224490000700240520170100247100002301948700003701971700002402008700002102032856012502053       2018                        eng d00aIon pairing in 1-butyl-3-methylpyridinium halide ionic liquids studied using NMR and DFT calculations0 aIon pairing in 1butyl3methylpyridinium halide ionic liquids stud  cAPR  a11470-114800 v203 aWe present the H-1, C-13 and N-15 NMR chemical shifts of bulk ionic liquids based on 1-butyl-3-methylimidazolium (the cation also known as 1-butyl-3-picolinium) halides (Cl-, Br- and I-) and tribromide (Br-3(-)) salts. A characterization in solution of the analogous ICl2- and I-3(-) salts is also reported. A series of DFT calculations has been run to predict the features of the NMR spectra of the pure ILs based on a few selected supramolecular ionic aggregates. To test the effect of temperature, and vibrational and conformational motions, only for the chloride salt, we also run first-principles molecular dynamics simulations of the ion pair in the gas phase, using the ADMP scheme (Atom Centered Density Matrix Propagation molecular dynamics model). The aim of our investigation is to test whether a simple DFT based approach of ion-pairing in ionic liquids is capable of providing reliable results and under which conditions the protocol is robust. We obtained a very good agreement between the calculated and experimental spectra for the three halides, where the bulk structure of the ILs is dominated by H-bond interactions between the X- anion (X = Cl, Br and I) and the ortho protons of the pyridinium ring (a structural arrangement not too different from the solid-state structure of pyridinium halides). In contrast, when the H-bond is weak, as in the Br-3(-) case, a number of supramolecular arrangements exist in solution and the simple DFT calculations of a few selected cases cannot exhaustively explore the complete energy landscape. Moreover, the dynamic effects due to thermal motion, evaluated by ADMP MD simulations of the chloride salt, appear to be not very significant.1 aSwamy, Vincent, P.1 aThulasiram, Hirekodathakallu, V.1 aRastrelli, Federico1 aSaielli, Giacomo  uhttps://library.ncl.res.in/content/ion-pairing-1-butyl-3-methylpyridinium-halide-ionic-liquids-studied-using-nmr-and-dft02053nas a2200205   4500008004100000022001400041245009300055210006900148260000800217300001200225490000700237520137800244100001401622700002501636700002001661700002301681700001801704700002101722856010401743       2020                        eng d  a1744-683X00aInfluence of the ion size on the stability of the smectic phase of ionic liquid crystals0 aInfluence of the ion size on the stability of the smectic phase   cJAN  a411-4200 v163 a<p>The thermotropic phase behavior of ionic liquids and ionic liquid crystals based on novel N-alkyl-3-methylpyridinium halides, trihalides and dichloroiodates was experimentally studied by polarized optical spectroscopy (POM) and differential scanning calorimetry (DSC) as well as by molecular dynamics (MD) simulation. In the experiments, the existence and thermal range of stability of the smectic phase of these ionic liquid crystals are found to strongly depend on the volume ratio between the cation and anion, that is their relative size. Only compounds with a relatively large volume ratio of the cation to anion, i.e., those with longer cationic alkyl chains and monoatomic halide anions, have a stable smectic A phase. Both melting points and clearing points increase with such a ratio. The MD simulation results qualitatively agree very well with the experimental data and provide molecular details which can explain the experimentally observed phenomena: the stronger van der Waals interactions from the longer alkyl chains and the stronger electrostatic interactions from the smaller anions with a higher charge density increase the stability of both the crystal phase and the smectic phase; this also prevents the ionic layers from easily mixing with the hydrophobic regions, a mechanism that ultimately leads to a nanosegregated isotropic liquid phase.</p>
1 aCao, Wudi1 aSenthilkumar, Beeran1 aCausin, Valerio1 aSwamy, Vincent, P.1 aWang, Yanting1 aSaielli, Giacomo  uhttps://library.ncl.res.in/content/influence-ion-size-stability-smectic-phase-ionic-liquid-crystals