B27−: Appearance of the smallest planar boron cluster containing a hexagonal vacancy

Abstract

Photoelectron spectroscopy and ab initio calculations have been carried out to probe the structures and chemical bonding of the B27 (-) cluster. Comparison between the experimental spectrum and the theoretical results reveals a two-dimensional (2D) global minimum with a triangular lattice containing a tetragonal defect (I) and two low-lying 2D isomers (II and III), each with a hexagonal vacancy. All three 2D isomers have 16 peripheral boron atoms and 11 inner boron atoms. Isomer I is shown to be mainly responsible for the observed photoelectron spectrum with isomers II and III as minor contributors. Chemical bonding analyses of these three isomers show that they all feature 16 localized peripheral B-B σ-bonds. Additionally, isomer I possesses 16 delocalized σ bonds and nine delocalized π bonds, while isomers II and III each contain 17 delocalized σ bonds and eight delocalized π bonds. It is found that the hexagonal vacancy is associated generally with an increase of delocalized σ bonds at the expense of delocalized π bonds in 2D boron clusters. The hexagonal vacancy, characteristic of borophenes, is found to be a general structural feature for mid-sized boron clusters. The current study shows that B27 (-) is the first boron cluster, where a hexagonal vacancy appears among the low-lying isomers accessible experimentally.

B 36 borophene as an electronic sensor for formaldehyde: Quantum chemical analysis

“…Until now, numerous studies have focused on the graphene-like inorganic and all-boron monolayers because they are of great importance as graphenes [33][34][35][36][37][38][39][40][41][42][43]. Since all-boron honeycomb hexagonal networks are electron deficient, it has been found that B atoms cannot generate these kinds of structures [42].…”

The Planar CoB18− Cluster as a Motif for Metallo‐Borophenes

“…Thep eripheral BÀBb ond lengths in CoB 18 À are between 1.56 a nd 1.65 , smaller than those of the interior B À Bbonds (1.66-1.90 ), consistent with those found for bare planar boron clusters. [3][4][5][6][7][8][9][10] Theseven Co À Bb ond lengths range from 1.91 t o2 .08 , which are close to the Co-B single bond length (1.96 ) using the selfconsistent covalent radii of Pyykkç. [49] Therefore,the Co atom has optimal bonding with the seven boron atoms in its first coordination shell, giving rise to the high stability of the planar CoB 18 À cluster.I ts hould be pointed out that CoB 8 À was found previously to be ah ighly stable borometallic molecular wheel with D 8h symmetry,i nw hich the B À Ba nd CoÀBb ond lengths are 1.56 and 2.03 , respectively.…”

“…In size-selected boron clusters for n > 9, truly planar structures always involve at etragonal, pentagonal, or hexagonal defects. [5][6][7][8][9][10] At riangular lattice always display out-of-plane distortions,j ust like in the infinitely large monolayer boron with atriangular lattice. [11][12][13][14] In the finite system, the peripheral BÀBb onds are stronger with shorter bond lengths due to dangling bonds,which create strains in the interior of the planar boron clusters.T his strain can be released either by out-of-plane distortions or nontriangular defects.However,inthe C 2v planar CoB 18 À the Co À Bb ond distance is longer than typical interior B À Bb onds, and, therefore,t he hetero-atom helps relieve the strain created by the short peripheral BÀBbonds to allow aperfectly planar structure.T his observation suggests that different transition-metal or f-element atoms may be doped into monolayer borons to create hetero-borophenes.T hus, doping can be another handle to tune the properties of borophenes,w hich is not available to graphene.W ith transition metals and rare-earth elements,i ti sc onceivable to create metallo-borophenes with tunable magnetic, optical, and non-linear optical properties.T he low oxidation state observed for the Co atom in CoB 18 À suggests that such metallo-borophenes may also have interesting chemical and catalytic properties.…”

“…[2] In the molecular and nano-scale,b oron also displays interesting chemical structures and bonding.O ver the past decade,j oint experimental and theoretical studies have uncovered af ascinating landscape for size-selected boron clusters,ranging from planar structures to fullerene-like cage structures (borospherenes). [3][4][5][6] In contrast to bulk boron, sizeselected boron clusters (B n À )have been found to be planar or quasi-planar (2D) up to 27 atoms as anions, [7] and continue to be 2D at n = 30, 35, and 36. [8][9][10] Due to its electron deficiency, boron cannot form hexagonal monolayers like graphene, whereas at riangular boron lattice obtained by filling ah exagonal boron layer was predicted to be buckled.…”

Structural Evolution and Chemical Bonding of Diniobium Boride Clusters Nb2Bx–/0 (x = 1–6): Hexagonal‐Bipyramidal Nb2B6–/0 Species

“…Due to the nature of electron deficiency and small covalent radius, boron clusters have the tendency to shape planar and quasiplanar structures, which contrast markedly with the three‐dimensional (3D) structures in bulk boron and many solid boron compounds. During the past few decades, the size of boron clusters with planar or quasiplanar geometries has been considerably extended by experimental and theoretical work . Among them, B 16 + has been reported to be the smallest cationic cluster that undergoes a transition between the two‐dimensional (2D) quasiplanar and the 3D structures .…”