Thermodynamic parameters of the pedal motion in the crystal structures of two bromomethylated azobenzenes
Vande Velde, Christophe M.L.
Faculty of Sciences. Chemistry
Faculty of Applied Engineering Sciences
, p. 5751-5756
University of Antwerp
Two bromomethylated azobenzene derivatives were characterized by X-ray crystallography at 100 K after fast cooling, and showed disorder of the central N-atoms. The structures were re-determined over a range of temperatures, providing evidence for dynamic disorder due to pedal motion of the central N[double bond, length as m-dash]N bond. Using van't Hoff plots, thermodynamic parameters for the pedal motion were determined. Computationally very cheap AtomAtom-Force Field (AA-CLP) calculations were employed, which showed that the differences in dynamic disorder enthalpy between the two compounds are predominantly due to intermolecular interactions. AA-CLP calculations and gas phase electronic structure calculations were employed to show the link between intermolecular interactions and activation energy for pedal motion.