MB 8 2− (M = Be, Mg, Ca, Sr, and Ba): Planar octacoordinate alkaline earth metal atoms enclosed by boron rings

Abstract

Complexes involving planar octacoordinate alkaline earth metal atoms in the centers of eight-membered boron rings have been investigated by two density functional theory (DFT) methods. BeB 8 2 with D 8h symmetry is predicted to be stable, both geometrically and electronically, since a good match is achieved between the size of the central beryllium atom and the eight-membered boron ring. By contrast, the other alkaline earth metal atoms cannot be stabilized in the center of a planar eight-membered boron ring because of their large radii. By following the out-of-plane imaginary vibrational frequency, pyramidal C 8v MgB 8 2 , CaB 8 2 , SrB 8 2 , and BaB 8 2 structures are obtained. The presence of delocalized  and  valence molecular orbitals in D 8h BeB 8 2 gives rise to aromaticity, which is reflected by the value of the nucleus-independent chemical shift. The D 8h BeB 8 2 structure is confirmed to be the global minimum on the potential energy surface.density functional theory, octacoordinate, alkaline earth metal, aromatic, molecular orbital

Spatial and Electronic Structures of BeB8 and MgB8: How far Does the Analogy Go?

“…The distance between the central boron atoms and boron atoms on the perimeter is 185.6 pm in BeB 8 , and 181.6 in MgB 8 , while the boron‐boron bond length along the B 7 ring is 153.1 pm in BeB 8 and 154.3 pm in MgB 8 . The found geometrical parameters of the boron rings are similar to those reported for BeB 8 2− and MgB 8 2− [86] …”

“…If Be is changed with Mg the obtained boron‐based clusters usually exhibit very different spatial‐ and electronic‐structure properties. For instance, BeB 8 2− has a planar wheel D 8h structure, whilst MgB 8 2− takes the pyramidal C 8v form [57] . Furthermore, Mg 2 B 8 exhibits a compass like structure with a very characteristic dynamical behaviour, [59] while Be 2 B 8 adopts the sandwich‐like structure [60] .…”

“…It was found that doping with the alkali or alkaline-earth atoms give rise to variety of boronbased structures, such as sandwich, [40] inverse sandwich [43] or wheel-like structures. [56,57] Among the alkaline-earth metals, Be has shown to be very useful in stabilizing monocyclic boronstructures. [44,45,58] If Be is changed with Mg the obtained boronbased clusters usually exhibit very different spatial-and electronic-structure properties.…”

Probing the structure and electronic properties of beryllium doped boron clusters: A planar BeB16− cluster motif for metallo-borophene

“…For plane and quasi-planar structures, the coordinate number of Be atom is interesting. The BeB n 0/− ( n = 10, 12, 14, 16) and BeB 18 − feature heptacoordinate and the BeB 11 − and BeB n 0/− ( n = 13, 15) possess octacoordinate, while the BeB 17 0/− are quasi-planar hexacoordinate structures due to the attribute of Be atom 59,60 . This evident structures evolution pattern contributes to form plane clusters of BeB n 0/− , which are potential two-dimensional material.…”

Structural transformations in boron clusters induced by metal doping

“…113 Pu et al noted that this shape does not occur with any other anionic system with a group 2 element. 119 B 8 Fe 2− is also a planar molecular wheel with Fe at the center. 120 If the Fe atom is substituted by Co, the D 8h form is maintained for the neutral and anionic cases.…”