Dynamic Mg 2 B 8 Cluster: A Nanoscale Compass

Boron‐based binary cluster Mg 2 B 8 is shown to adopt a compass‐like structure via computational global searches, featuring an Mg 2 dimer as the needle and a disk‐shaped B 8 molecular wheel as baseplate. The nanocompass has a diameter of 0.35 nm. Born–Oppenheimer molecular dynamics simulations indicate that Mg 2 B 8 is structurally fluxional with the needle rotating freely on the baseplate, analogous to a functioning compass. The dynamics is readily initiated via a ultrasoft vibrational mode. The rotational barrier is only 0.1 kcal mol −1 at the single‐point CCSD(T) level. Chemical bonding analysis suggests that the cluster compass can be formulated as [Mg 2 ] 2+ [B 8 ] 2− ; that is, the baseplate and the needle are held together primarily through ionic interactions. The baseplate is doubly aromatic with π and σ sextets. The bonding pattern provides a dilute, continuous, and delocalized electron cloud, which underlies the dynamics of the nanocompass.