Atomistic insight into orthoborate-based ionic liquids: Force field development and evaluation
Journal of Physical Chemistry B
Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91, Stockholm, Sweden; Chemistry of Interfaces, Luleå University of Technology, S-971 87, Luleå, Sweden; System and Component Design, KTH Royal Institute of Technology, S-10 044, Stockholm, Sweden; Mechanical Construction and Production, Ghent University, B-9000 Ghent, Belgium; Department of Physics, Warwick University, CV4 7AL, Coventry, United Kingdom; Stellenbosch Institute of Advanced Studies (STIAS), Wallenberg Research Centre, Stellenbosch University, Marais Street, Stellenbosch 7600, South Africa
We have developed an all-atomistic force field for a new class of halogen-free chelated orthoborate-phosphonium ionic liquids. The force field is based on an AMBER framework with determination of force field parameters for phosphorus and boron atoms, as well as refinement of several available parameters. The bond and angle force constants were adjusted to fit vibration frequency data derived from both experimental measurements and ab initio calculations. The force field parameters for several dihedral angles were obtained by fitting torsion energy profiles deduced from ab initio calculations. To validate the proposed force field parameters, atomistic simulations were performed for 12 ionic liquids consisting of tetraalkylphosphonium cations and chelated orthoborate anions. The predicted densities for neat ionic liquids and the [P6,6,6,14][BOB] sample, with a water content of approximately 2.3-2.5 wt %, are in excellent agreement with available experimental data. The potential energy components of 12 ionic liquids were discussed in detail. The radial distribution functions and spatial distribution functions were analyzed and visualized to probe the microscopic ionic structures of these ionic liquids. There are mainly four high-probability regions of chelated orthoborate anions distributed around tetraalkylphosphonium cations in the first solvation shell, and such probability distribution functions are strongly influenced by the size of anions. © 2014 American Chemical Society.
Calculations; Chelation; Distribution functions; Oil field development; Positive ions; Probability distributions; Ab initio calculations; Atomistic simulations; Energy components; Force field development; Force field parameters; Radial distribution functions; Solvation shell; Vibration frequency; Ionic liquids