We resorted to three coordinate systems to describe the reaction coordinate and significant secondary movements. Firstly, a cartesian coordinate system, obtained by combining all simulations and aligning them on the rigid phenanthroline bridge. This helps mitigate the impact of rotational and translational movements of the system during the simulations. Secondly, we generated a set of internal coordinates for all trajectories, using the MDanalysis package. This has the advantage of removing the issue of noise due to alignment artefacts, yet introduces more correlational effects. Thirdly, we generated a reduced set of internal coordinates, describing highly rigid chemical moieties by their centre of mass (see SI Section 3 for details).