Theoretical Study On The Structural And Electronic Properties Of Alkali Metal Doped Boron Clusters

The doped boron clusters with metals have been achieved in a large amount of species with intriguing electronic and structural properties.In the case of the doped boron systems,the dopant is responsible for the new topology that does not exist in the pure boron clusters,meanwhile,such topology of boron motifs also strongly affects electronic properties and bonding of dopants.In this dissertation,the structural and electronic properties,stability of alkali-doped boron clusters are studied theoretically using the high-level calculations.The main research contents are as follows:1.Lithium doped tubular structure in LiB₂₀0 and LiB^–₂₀:a viable global minimumWe present a strategy by which the stability of tubular boron clusters can be significantly enhanced by doping the B₂₀0 cluster with a lithium atom.High-level quantum chemical calculations showed that the lowest energy structures of LiB₂₀0 and LiB₂₀^–are tubular structures with D_10d0d symmetry,in which the lithium atom is located at the center of the tubular structure.Chemical bonding analysis revealed that the high-symmetry tubular boron clusters are characterized as charge transfer complexes(Li⁺B₂₀^–and Li⁺B₂₀^2-),resulting in double aromaticity with delocalized?+?bonding and strong electrostatic interactions between cationic Li⁺and tubular boron motifs with twenty Li–B interactions.The unique bonding pattern of the LiB₂₀0 and LiB^–₂₀species provides a key driving force to stabilize tubular structures over quasi-planar structures,suggesting that electrostatic interactions resulting from alkali metals might unveil a new clue to the structural evolution of boron clusters2.Structural and electronic properties of MB₂₂^–?M=Na,K?clusters:tubular boron versus quasi-planar boron formsElectron deficiency of boron atom has led to the abundant chemical propertiesof boron clusters,such as intriguing structures,unique multi-center bonding and electronic properties,as well as the structural evolution from planar to three-dimensional forms.Tubular boron clusters or all-boron fullerenes serve as an important indicator for the structural evolution of boron clusters.Moreover,tubular boron clusters can be considered as precursors for boron nanotubes.However,the anionic tubular boron clusters have been theoretically identified to be less stable in comparison to the planar or quasi-planar forms,which is clearly disadvantageous for the gas-phase experimental characterization.In this study,we follow the strategy that the stability of the tubular boron clusters can be significantly enhanced by doping alkali metals,suggesting MB₂₂^–?M=Na,K?as the largest anionic boron nanotube predicted until now.The title tubular boron clusters were more stable than the quasi-planar forms because of the double aromaticity with the delocalized?+?electrons in boron motifs as well as the optimal electrostatic interactions between the cationic M⁺and anionic tubular boron motifs,originating from the strong charge transfer from the alkali metals to the boron motifs.