Insights from density functional theory into the formation and rotation of an enantiospecific assembly of molecular raffle wheels

We have performed a joint theoretical and experimental study of the assembly formed when BPP-COOH ( 2,6-bis(1H-pyrazol-1-yl)pyridine-4-carboxylic acid) is deposited on Ag(111). Three-fourths of the molecules form a rigid Kagome 'host' network. The cavities of this network are occupied by the remaining 'guest' molecules, which display a punctuated rotation between positions corresponding to global minima in the rotational energy landscape. Calculations show that the topography of this landscape can be explained by the making and breaking of hydrogen bonds between the guest molecules and the host network. The height of the rotational barrier computed theoretically is in excellent agreement with that extracted from temperature-dependent experiments. The host network also bestows enantiospecificity on the system, due to the twist between the host network and the underlying Ag(111) surface.