Computational Investigation into Ligand Effects on Correlated Geared Dynamics in Dirhodium Supramolecular Gears-Insights Beyond the NMR Experimental Window.

The rotational dynamics of dirhodium supramolecular gears, formed with four 9-triptycene carboxylates cyclically arranged around a dirhodium core with variable axial ligands as originally designed by Shionoya et al., provide an excellent opportunity to evaluate the potential of computational methods and expand our understanding of the factors determining geared dynamics. Rotational dynamic rates in these structures depend on the nature of the axial ligand as shown by simulations over timescales that are not accessible experimentally. Molecular dynamics simulations gave information on the gearing mechanism, and the activation barriers to gearing were calculated using density functional theory. Steric demands imposed by the axial ligand were quantified using buried volume analysis. We found that gearing takes place in all six dirhodium-gear complexes with different axial ligands and that rotational barriers depend on their steric size.