Browsing by Author "Srivastava, Nitin"

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Complementing Crystallography with Ultralow-Frequency Raman Spectroscopy: Structural Insights into Nitrile-Functionalized Ionic Liquids
(2016-01-04)
Chen, Hong-Kai
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Srivastava, Nitin
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Saha, Satyen
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Shigeto, Shinsuke
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應用化學系
Functionalized ionic liquids are a subclass of ionic liquids that are tailored for a specific application. Structural characterization in both solid and liquid phases is central to understanding their physical properties. Here, we used ultralow-frequency Raman spectroscopy, which can measure Raman spectra down to approximately 5cm(-1), to study the structures and physical properties of 1-(4-cyanobenzyl)-3-methylimidazolium salts with five different anions. A comparison of the observed low-frequency Raman spectral patterns enabled us to predict the crystal symmetry of one of the synthesized salts for which single-crystal X-ray diffraction data were unobtainable. Real-time tracking of the low-frequency Raman spectral changes during melting revealed peak shifts indicative of different degrees of microscopic heterogeneity in the ionic liquids. The results show that our method provides a facile means that is complementary to X-ray crystallography, for obtaining structural information of ionic liquids.
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.