title: Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations.
abstract: Description of the local microscopic structure in ionic liquids (ILs) is a prerequisite to obtain a comprehensive understanding of the influence of the nature of ions on the properties of ILs. The local structure is mainly determined by the spatial arrangement of the nearest neighboring ions. Therefore, the main interaction patterns in ILs, such as cation-anion H-bond-like motifs, cation-cation alkyl tail aggregation, and ring stacking, were considered within the framework of the nearest-neighbor approach with respect to each particular interaction site. We employed classical molecular dynamics (MD) simulations to study in detail the spatial, radial, and orientational relative distribution of ions in a set of imidazolium-based ILs, in which the 1-butyl-3-methylimidazolium (C4mim(+)) cation is coupled with the acetate (OAc(-)), chloride (Cl(-)), tetrafluoroborate (BF4(-)), hexafluorophosphate (PF6(-)), trifluoromethanesulfonate (TfO(-)), or bis(trifluoromethanesulfonyl)amide (TFSA(-)) anion. It was established that several structural properties are strongly anion-specific, while some can be treated as universally applicable to ILs, regardless of the nature of the anion. Namely, strongly basic anions, such as OAc(-) and Cl(-), prefer to be located in the imidazolium ring plane next to the C-H(2/4-5) sites. By contrast, the other four bulky and weakly coordinating anions tend to occupy positions above/below the plane. Similarly, the H-bond-like interactions involving the H(2) site are found to be particularly enhanced in comparison with the ones at H(4-5) in the case of asymmetric and/or more basic anions (C4mimOAc, C4mimCl, C4mimTfO, and C4mimTFSA), in accordance with recent spectroscopic and theoretical findings. Other IL-specific details related to the multiple H-bond-like binding and cation stacking issues are also discussed in this paper. The secondary H-bonding of anions with the alkyl hydrogen atoms of cations as well as the cation-cation alkyl chain aggregation turned out to be poorly sensitive to the nature of the anion.
authors.affiliation: LASIR, University of Lille-Science and Technology (UMR CNRS A8516) , Bâtiment C5, Cité Scientifique, 59655, Villeneuve d'Ascq Cedex, France.|Centre d'Etudes et de Recherche sur le Médicament de Normandie (CERMN), UNICAEN, FR CNRS INC3M , Boulevard Becquerel, Caen, 14032 Cedex, France.
authors.forename: Bogdan A
authors.initials: BA
authors.lastname: Marekha
authors.affiliation: LASIR, University of Lille-Science and Technology (UMR CNRS A8516) , Bâtiment C5, Cité Scientifique, 59655, Villeneuve d'Ascq Cedex, France.|Department of Inorganic Chemistry, V. N. Karazin Kharkiv National University , Svobody Square, 4, Kharkiv, 61022, Ukraine.
authors.forename: Volodymyr A
authors.initials: VA
authors.lastname: Koverga
authors.affiliation: LASIR, University of Lille-Science and Technology (UMR CNRS A8516) , Bâtiment C5, Cité Scientifique, 59655, Villeneuve d'Ascq Cedex, France.
authors.forename: Erwan
authors.initials: E
authors.lastname: Chesneau
authors.affiliation: Department of Inorganic Chemistry, V. N. Karazin Kharkiv National University , Svobody Square, 4, Kharkiv, 61022, Ukraine.
authors.forename: Oleg N
authors.initials: ON
authors.lastname: Kalugin
authors.affiliation: Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University , Honjo-machi, Saga 840-8502, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takamuku
authors.affiliation: Department of Chemistry, Eszterházy Károly University , Leányka Utca 6, H-3300 Eger, Hungary.|MTA-BME Research Group of Technical Analytical Chemistry, Szent Gellért tér 4, H-1111 Budapest, Hungary.
authors.forename: Pál
authors.initials: P
authors.lastname: Jedlovszky
authors.affiliation: LASIR, University of Lille-Science and Technology (UMR CNRS A8516) , Bâtiment C5, Cité Scientifique, 59655, Villeneuve d'Ascq Cedex, France.
authors.forename: Abdenacer
authors.initials: A
authors.lastname: Idrissi