On the coordination of Zn2+ ion in Tf2N− based ionic liquids: structural and dynamic properties depending on the nature of the organic cation. Issue 4 (10th January 2018)

• Record Type: Journal Article
• Authors: Sessa, Francesco; Migliorati, Valentina; Serva, Alessandra; Lapi, Andrea; Aquilanti, Giuliana; Mancini, Giordano; D'Angelo, Paola
• Is Part Of: Physical chemistry chemical physics. Volume 20:Issue 4(2017)
• Page Start: 2662
• Page End: 2675
• Publication Date: 2018-01-10
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp07497b
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The Zn 2+ coordination structure changes when the Zn(Tf2 N)2 salt is dissolved in ionic liquids resulting in more favorable interactions among solvent cations and anions. Abstract : A synergic approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy has been used to investigate diluted solutions of zinc bis(trifluoromethanesulfonyl)imide (Zn(Tf2 N)2 ) in Tf2 N − based ionic liquids (ILs) having different organic cations, namely the 1-butyl-3-methylimidazolium ([C4 (mim)] + ), 1, 8-bis(3-methylimidazolium-1-yl)octane ([C8 (mim)2 ] 2+ ), N, N, N -trimethyl- N -(2-hydroxyethyl)ammonium ([Choline] + ) and butyltrimethylammonium ([BTMA] + ) ions. All of the ILs tend to dissolve the Zn(Tf2 N)2 species giving rise to a different structural arrangement around the Zn 2+ as compared to that of the salt crystallographic structure. A quantitative analysis of the Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra of the solutions has been carried out based on the microscopic description of the systems derived from the MD simulations. A very good agreement between theoretical and experimental EXAFS signals has been obtained, allowing us to assess the reliability of the MD structural results for all the investigated solutions. The Zn 2+ ion has been shown to be coordinated by six oxygen atoms of the Tf2 N − anions arranged in an octahedral geometry in all the Tf2 N − based ILs, regardless of the organic cation of the IL solvent. However, the nature of the organic cation has a small influence on the overall spatial arrangement of the Tf2 N − anions in the Zn 2+ first solvation shell: two different Zn–Tf2 N complexes are found in solution, a 5-fold one, with one bidentate and four monodentate Tf2 N − anions, and a 6-fold one with only monodentate ligands, with the ratio between the two species being slightly dependent on the IL cation. The IL ion three-dimensional arrangements in the different IL solutions were also investigated by carrying out a thorough analysis of the MD simulations, highlighting similarities and differences between imidazolium and ammonium based IL systems.