Weak intra and intermolecular interactions via aliphatic hydrogen bonding in piperidinium based ionic Liquids: Experimental, topological and molecular dynamics studies

Hydrogen bonding interaction plays an important role in the stability of the building blocks of various materials. In present work, both intra- and inter- molecular aliphatic H-bond interactions stabilize piperidinium based ionic liquids (ILs: MPDNP, PPDNP, BPDNP and HPDNP) and play crucial role on physical properties of these ILs. Further, the significance of multiple intermolecular aliphatic H-bonding interactions in the formation of molecular clusters, ion-pair, dimeric ion-pairs, and also corrugated sheet array of ILs has been investigated here. UV-vis study of these ILs has also been performed to understand the electronic properties of these ILs in solution. The DSC, TGA, SCXRD, vibrational spectroscopic techniques have been employed to understand the effect of intra and intermolecular aliphatic hydrogen bonding interaction on physical property and molecular cluster formation of ILs in their ambient phases. The DSC and TGA studies demonstrate that the intermolecular interaction between cation and anion remains nearly unvaried on increasing of alkyl chain length but the physical properties of ILs changes. SCXRD and vibrational spectroscopic techniques describe the presence of aliphatic H-bonding interaction between ion pairs, dimeric ion-pairs and corrugated sheet having contacts in the range 2.46-2.63 angstrom. NBO analysis is performed to calculate the second order stabilization energy for better understanding of the intramolecular interactions at a molecular level. The second order stabilization energy for the transfer lone pair charge of oxygen to antibonding orbital of CAH is measured in the range of 3.46-3.73 Kcal/mol for ILs. Topological and ab initio molecular dynamics (AIMD) simulations studies are performed to get closer insight of underlying interactions and the stability of ILs. AIMD study depicts that the total energy of IL attains a maximum of -1045.84 a.u. close to 100 fs, whereas relatively low energy is measured between 250 and 350 fs.