Dynamic Mg2B8 Cluster A Nanoscale Compass

   Abstract: Boron-based binary cluster Mg₂B₈is shown to adopt a compass-like structure via computational global searches, featuring an Mg₂ dimer as the needle and a disk-shaped B₈ molecular wheel as baseplate. The nanocompass has a diameter of 0.35 nm. Born–Oppenheimer molecular dynamics simulations indicate that Mg₂B₈is structurally fluxional with the needle rotating freely on the baseplate, analogous toafunctioning compass. The dynamics is readily initiated via a ultrasoft vibrational mode. The rotational barrier is only 0.1 kcalmol^–1at the single point CCSD(T) level. Chemical bonding analysis suggests that the cluster compass can be formulated as [Mg2 ]²⁺[B₈]^2–; that is, the baseplate and the needle are held together primarily through ionic interactions. The baseplate is doubly aromatic with p and s sextets. The bonding pattern provides a dilute, continuous, and delocalized electron cloud, which underlies the dynamics of the nanocompass.