Theoretical Study On The Structural Evolution And Stabilization Mechanism Of Lithium And Beryllium Metal Doped Boron Clusters

Since the discovery of fullerenes such as C60 in the 1980s,their widespread application value in various fields has attracted extensive research interests in atomic clusters.In recent years,numerous studies on boron clusters have demonstrated that the electron deficiency of boron leads to boron clusters exhibiting abundant geometric structures and novel electronic structures,which has aroused widespread attention in the study of boron clusters.Compared to pure boron clusters,metal doped boron clusters not only effectively regulate the structural evolution of boron clusters,but also obtain a series of metal doped boron clusters with high symmetry structures,such as planar,half-sandwich,tubular,cage,core-shell,etc.So far,the transition metal doped boron clusters have been systematically studied,in which the rich d-orbital electrons of transition metal atoms lead to the unique structural evolution and novel electronic structures of boron clusters.In the metal doped boron cluster systems,the research of alkali metal and alkaline earth metal doped boron cluster is relatively rare.However,exploring the structural evolution and stabilization mechanism of boron clusters caused by alkali metal and alkaline earth metal doped is a topic worthy of attention.In this paper,we use lithium(Li)and beryllium(Be),which have small atomic radius and strong electronegativity in alkali metal and alkaline earth metal,as the doping atoms to systematically reveal the structural evolution and growth mechanism of boron clusters,and further obtain boron clusters with novel geometric and electronic structures.It provides an important theoretical vision for the study of the stabilization mechanism of boron clusters.The main contents and results are outlined as follows:1.Tubular boron clusters can be considered not only as a key indicator of the twodimensional planar to three-dimensional structural transition of boron clusters,but also as embryos for boron nanotubes.While some tubular boron or metal-doped boron clusters have been obtained as discussed above,most of them are two-ring tubular cases,and their higher-ring analogues are very scarce,especially the four-ring system has not been reported.In order to explore the evolution mechanism and stabilization mechanism of the tubular boron clusters,the MB24q and M2B24q(M=alkali metal and alkaline earth metals)in neutral and their monocharged states are first considered.Global minimum searches and energy confirmation revealed that the most stable structure of Li2B24 is a three-ring tubular structure and the most stable structure of Be2B24+is a four-ring tubular structure,and obtained the stabilization mechanism of alkali metal and alkaline earth metal doped tubular boron clusters.Chemical bonding analysis of Be2B24+clusters revealed that the unique ability of beryllium to make strong covalent and electrostatic interactions makes the Be2B24+cluster stable in such an unusual geometry.2.In this paper,we systematically investigated the alkali metal and alkaline earth metal Li and Be doped LinB12(n=1-3)and BenB12+/0/-(n=1-4)systems.It is found that the drastic structural change from the quasi-planar B12 cluster to the tube or cage shape occurs upon the addition of such simple dopant,and obtaining the first cage Be4B 12+(similar to an Archimedean solid)cluster close to Td symmetry.The chemical bonding analysis of highly symmetric cage Be4B12+clusters revealed that the strong electrostatic interaction and even stronger covalent interaction between Be atoms and boron skeleton are not only the main driving forces for the two-dimensional to three-dimensional structural transition of B12 clusters,give rise to the high stability of highly symmetric cage boron clusters.This work systematically reveals the important influence of alkali metal and alkaline earth metal atoms on the structural evolution of boron clusters,which unveils a new idea for designing novel borospherenes.3.Due to the similarity of their delocalized π-electrons,certain planar boron clusters are considered as analogues of arenes.It is well-known that small arenes can form sandwich compounds with transition metal elements,such as,(C5H5)2Fe.However,the formation of sandwich complexes with boron motifs has not been reported thus far.This is primarily attributed to thermodynamic factors,as the boron fragments tend to fuse with each other rather than exist as isolated entities required for a sandwich structure.We consider boron motifs interacting with beryllium Bem rings,where m in BnBemBn corresponds to the number of peripheral B-B bonds in the Bn wheels.Our findings reveal that sandwich isomers cannot be energetically favored for Bn(n=3-5,12-14)boron wheels as the boron frameworks preferentially fuse through B-B bonds at the peripheral and central boron positions,respectively.Among the remaining cases,although sandwiches are possible,they are relatively high in energy,except for a particular combination.B7Be6B7.Chemical bonding analysis reveals that the B7Be6B7 complex can be viewed as[B7]3-[Be6]6+[B7]3-complex(where B73-is the boron analogues of C5H5-),and stability of the B7Be6B7 complex arises from a combination of strong electrostatic and significant covalent interactions between Be6 and B7.