Browsing by Author "Panja, Sumit Kumar"

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Evidence of C-F-P and aromatic pi-F-P weak interactions in imidazolium ionic liquids and its consequences
(2018-04-05)
Panja, Sumit Kumar
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Srivastava, Nitin
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Srivastava, Jyoti
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Prasad, Namburi Eswara
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Noothalapati, Hemanth
A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF(6) IL to cmimPF(6) IL The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and pi cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C-2-F-P and pi-F-P) in cmimPF(6) but are absent in structurally similar prototype IL bmimPF(6). Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF(6) IL compared to bmimPF(6) IL These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions. (C) 2017 Elsevier B.V. All rights reserved.
Significance of weak interactions in imidazolium picrate ionic liquids: spectroscopic and theoretical studies for molecular level understanding
(2015-01-01)
Panja, Sumit Kumar
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Dwivedi, Nidhi
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Noothalapati, Hemanth
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Shigeto, Shinsuke
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Sikder, A. K.
The effects of interionic hydrogen bonding and pi-pi stacking interactions on the physical properties of a new series of picrate anion based ionic liquids (ILs) have been investigated experimentally and theoretically. The existence of aromatic (C-2-H center dot center dot center dot O) and aliphatic (C-7-H center dot center dot center dot O-N-22 and C-6-H center dot center dot center dot O-N-20) hydrogen bonding and pi-pi stacking interactions in these ILs has been observed using various spectroscopic techniques. The aromatic and aliphatic C-H center dot center dot center dot O hydrogen bonding interactions are found to have a crucial role in binding the imidazolium cation and picrate anion together. However, the pi-pi stacking interactions between two successive layers are found to play a decisive role in tight packing in ILs leading to differences in physical properties. The drastic difference in the melting points of the methyl and propyl derivatives (mmimPic and pmimPic respectively) have been found to be primarily due to the difference in the strength and varieties of pi-pi stacking interactions. While in mmimPic, several different types of pi-pi stacking interactions between the aromatic rings (such as picrate-picrate, picrate-imidazole and imidazolium-imidazolium cation rings) are observed, only one type of pi-pi stacking interaction (picrate-picrate rings) is found to exist in the pmimPic IL. NMR spectroscopic studies reveal that the interaction of these ILs with solvent molecules is different and depends on the dielectric constant of the solvent. While an ion solvation model explains the solvation in high dielectric solvents, an ion-pair solvation model is found to be more appropriate for low dielectric constant solvents. The enhanced stability of these investigated picrate ILs compared with that of inorganic picrate salts under high doses of gamma radiation clearly indicates the importance of weak interionic interactions in ILs, and also opens up the possibility of the application of picrate ILs as prospective diluents in nuclear separation for advanced fuel cycling process.