Hydrogen bonding interactions in nicotinamide Ionic Liquids: A comparative spectroscopic and DFT studies Madhulata Shukla Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi, 221005, India article info Article history: Received 13 July 2016 Received in revised form 16 November 2016 Accepted 22 November 2016 Available online 23 November 2016 Keywords: Nicotinamide Ionic Liquids Spectroscopic studies DFT calculation Hydrogen bonding abstract Being biodegradable in nature nicotinamide based Ionic Liquids (ILs) are gaining much attention now a day. Nicotinamide iodide (i.e 1-methyl-3ethoxy carbonyl pyridinium iodide (mNicI)) and 1-methyl- 3ethoxy carbonyl pyridinium trifilimide (mNicNTf 2 ) new ILs has been synthesized and has been char- acterized using different spectroscopic techniques like NMR, UV visible and infrared spectroscopy. Theoretical studies have been performed on several nicotinamide ILs. Geometry and spectral features were further characterized by Density Functional Theory (DFT) calculation. NBO charge distribution and electrostatic potential diagram presents in depth knowledge about interactions between cation and anion. A comparative theoretical study between mNicI and its other analogues i. e 1-methyl-3 ethoxy carbonyl pyridinium chloride and bromide i. e mNicCl and mNicBr has also been performed. CeH/X hydrogen bonding along with C/X interaction has been reported for the first time for the nicotinamide based ILs. C2eH stretching frequency shifts to higher wavenumber with change to a lesser electroneg- ative anion. mNicCl and mNicBr are expected to be solid in nature with the evidence from the red shift in stretching frequency as compared to mNicI. TD-DFT calculation of mNicI proved that pale yellow color of liquid is due to inherent transition from anion to cation. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Research in the area of Ionic Liquids (ILs) continues to grow and their applications have broadened extensively now a days. ILs is of enormous importance as a huge amount of different ILs can be envisioned by the simple combination of different anions and cations. By varying the anion species or the cation entity (e.g. varying alkyl chain or the core), it is possible to change the physical properties as hydrophobicity, viscosity, density, and solubility and thus its influence towards the biological features [1]. Non-volatile nature of ILs under equipped conditions minimizes their effect on air quality during their life cycle in a chemical reaction. However, impact of ILs on soil and water is definitely of considerable concern at the time of their disposal. Hence using the technique to tune the properties of ILs as function of the chemical structure, one can design the ILs that would not just be ideal solvents for chemical processes, but would also be safe for disposal and would therefore be sustainable [2]. In this respect after a thorough study of Pyr- idinium based ILs by Harjani et al. the biodegradation of pyridine based ILs showed noticeably high levels of biodegradability over the 28 days period. Thus this study illustrate that the structural variation in the pyridinium skeleton may lead to the formation of desirable ILs which possess good solvent attributes and a tendency to biodegrade when released into an aquatic environment [3]. In this paper, we focused our attention on the ILs that were based on the ester moiety, as the introduction of this group in the pyridinium based ILs improved their biodegradation probably by providing a site for an enzymatic attack [4]. Hence our objective is to do syn- thesis and characterization of new pyridinium based IL which is supposed to be an efficient biodegradable solvent [5]. Synthesis and characterization of 1-methyl-3-ethoxy carbonyl pyridinium iodide (commonly called nicotinamide iodide, mNicI) and 1-methyl-3- ethoxy carbonyl pyridinium trifilimide (mNicNTf 2 ) ILs has been carried out and in-depth structural studies has been performed using DFT along with IR and NMR spectroscopic studies. CeH/X hydrogen bonding along with C/X interaction has been reported for the first time for the nicotinamide based ILs. Natural bond orbital (NBO) analysis was also performed to find out the charge transfer and the interaction between cation and anion. Pale yellow color of mnicI has been explained by using TDDFT calculation. Experimental observations have been well reproduced with the theoretical findings. E-mail address: madhu1.shukla@gmail.com. Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc http://dx.doi.org/10.1016/j.molstruc.2016.11.067 0022-2860/© 2016 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1131 (2017) 275e280