Predicting lanthanide boride inverse sandwich tubular molecular rotors with the smallest core-shell structure.

Lanthanide-boron binary clusters possess interesting structures and bonding which may provide insights into designing new boride nanomaterials. Inspired by the recently discovered mono-decker inverse sandwich D LaB (A') (1) and based on the extensive first-principles theory calculations, we predict herein the possible existence of a series of bi-decker inverse sandwich di-lanthanide boron complexes including D La[B] (A) (2), D La[B] (A) (3), and C La[B@B] (A) (4) which all contain a tubular B ligand (n = 18, 20) sandwiched by two La atoms at the two ends. In these novel clusters, La[B@B] (4) as a tubular molecular rotor with the smallest core-shell structure reported to date in boron-based nanoclusters possesses a B-bar rotating constantly and almost freely inside the B tube around it at room temperature. Detailed bonding analyses indicate that these complexes are stablized by effective (d-p)σ, (d-p)π, and (d-p)δ coordination interactions between the La centers and B bi-decker ligand. Six multi-center fluxional σ-bonds between the B-core and B tube in La[B@B] (4) are found to be responsible for its unique fluxional behaviors. The IR and Raman spectra of the concerned species are simulated to facilitate their experimental characterization.