Characterization and modeling of polyoxometalate-based ionic liquids. Force field refinement and insights into their dynamical behavior

Identifier:  imarina:9465818

Handle: https://hdl.handle.net/20.500.11797/imarina9465818

Authors:  Merimi K; Masip-Sánchez A; Zeaiter N; Camerel F; Cottyn-Boitte B; Roch-Marchal C; Floquet S; López X

Abstract:
Ionic liquids (ILs) are salts with melting points below 100 °C, being a more sustainable alternative to organic solvents because of their negligible vapor pressure and high thermal stability. The recently developed branch of polyoxometalate-based ILs (POM-ILs) incorporates the unique properties (redox, catalytic) of POMs to the advantages of ILs, opening the door to further advancements and applications in the field. In the present work we have synthesized and characterized new POM-ILs. Motivated by this progress and building upon current knowledge on simulations of classical ILs, we also propose a computational setup to describe the dynamic behavior of bulk POM-ILs through atomistic molecular dynamics simulations. The cationic part is an organic PR<inf>4</inf>⁺ unit, and POMs are well-known systems such as Lindqvist, Keggin and Wells-Dawson, among others. Part of the work presents variations made to the (reference) AMBER force field atomic parameters σ and ε, and their justification. We observe that changes applied remarkably affect the molecular mobilities (diffusivities or viscosities) of the system. Our analysis establishes that one set of the tested parameters reproduces the relative experimental viscosities for the family of compounds analyzed. Taking this setup, we further describe computationally the local and bulk dynamical properties, detailing the anion-cation interactions. One remarkable fact is that the experimental diffusivities are reproduced with very little microscopic molecular motion, that is, the mobility of the constituent parts is very limited, mostly restricted to a local position.