Exploring the structure of halomethanes with xenon: An NMR and MD investigation

Abstract

The liquid structure of dihalomethanes (CH2X2, X = Cl, Br, I) loaded with xenon gas was investigated both experimentally, by 129Xe NMR Spectroscopy, and computationally, by molecular dynamics (MD) simulations and relativistic DFT calculations. The chemical shifts of xenon have been measured in a wide range of temperatures; in addition, the spin-lattice relaxation times, T1, and the diffusion coefficients of dissolved xenon were also determined. The MD simulations of the three dihalomethanes with xenon dissolved were used to generate a collection of clusters, representing xenon with its first solvation shell, which was subsequently submitted to the relativistic DFT calculation of the 129Xe NMR shielding constant. This was finally averaged over the trajectory to obtain the corresponding chemical shift at various temperatures. The experimental data were then rationalized in terms of the density of the bulk phase and the average orientation of the halogens with respect to the xenon atom. Diffusion coefficients were also obtained from the MD simulations and compared with the experimental values, showing a good agreement.