Fluxional Behavior and Stability of the Cu2B8- Cluster: A Copper Borozene with a Freely Rotating Cu2 Dimer.

ABSTRACT

We demonstrate that Cu2B8- exhibits distinct fluxional behavior, akin to that of a functional stirrer, with the Cu2 dimer freely rotating on the B8 molecular wheel. This behavior is confirmed by Born-Oppenheimer molecular dynamics simulations. The initiation of this dynamic motion is facilitated by an ultrasoft vibrational mode (less than 10 cm-1), resulting in a negligible rotational barrier of 0.03 kcal/mol, as calculated at the single-point CCSD(T) level. The high stability of Cu2B8- arises from the strong interlayer electrostatic interaction between Cu2 and B8, due to charge transfer from Cu2 to B8, along with additional covalent interactions from the delocalized π electrons of the B8 wheel to the Cu2 dimer. Notably, the Cu2 dimer in Cu2B8- features a two-center one-electron Cu-Cu single bond, while the B82- moiety displays double aromaticity, characterized by the presence of six delocalized π electrons and six delocalized σ electrons.