σ-Aromaticity Planar Pentacoordinate Beryllium Atoms

Abstract

Six-valence-electron planar pentacoordinate beryllium (ppBe) is explored herein as a global minimum, which is only constructed by s-block metals in BeM 5 + (M = Cu, Ag, Au). The bonding in ppBe can be regarded as the excited-stated Be with a 2p x 1 2p y 1 electronic configuration, forming electron sharing with doublet M 5 + motifs followed by two sets of Be(p ∥ ) → [M 5 + ] σ donations and one Be(s) ← [M 5 + ] σ back-donation. Thus, the σ aromaticity originating from three delocalized σ orbitals gives rise to the whole stability of the high D 5h -symmetry ppBe and strongly enriches s-block planar hypercoordinate bonding.

Planar σ-Aromaticity in Ga-Doped Au Clusters

“…52 For example, the stability and planarity of the high-symmetry BeM 5 + (M = Cu, Ag, and Au) with the D 5h symmetry are mainly reinforced by σ-aromaticity. 53 Therefore, the σ-aromaticity in this paper is characterized by delocalized σ-bonding, after all MO, ELF, LOL, and NICS-scan results have been verified that the…”

“…Referring to the reference, Boldyrev et al in the review present examples of metal clusters, for which the use of σ-aromaticity concepts is essential for understanding chemical bonding and electron delocalization . For example, the stability and planarity of the high-symmetry BeM 5 + (M = Cu, Ag, and Au) with the D 5 h symmetry are mainly reinforced by σ-aromaticity . Therefore, the σ-aromaticity in this paper is characterized by delocalized σ-bonding, after all MO, ELF, LOL, and NICS-scan results have been verified that the valence electrons delocalize over the entire structures of Au 3 Ga and Au 5 Ga.…”

σ-Aromatic MAl6S6 (M = Ni, Pd, Pt) Stars Containing Planar Hexacoordinate Transition Metals

“…Planar hepta- and octacoordinate boron (p7B, p8B) centers can be stabilized in the beautiful molecular wheels B 8 − and B 9 − , which were experimentally observed by Zhai in 2003 [ 28 ]. The wheel-like ppB B 6 H 5 + , ppBe BeCu 5 , p8Be BeB 8 2− , p7Sc ScCu 7 , ppAl Cu 5 Al 2+ , ppGa Cu 5 Ga 2+ , and star-like ppB BBe 5 Au 5 , phGa GaBe 6 Au 6 were identified as the global minima [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Using size-selected anion photoelectron spectroscopy combined with ab initio calculations, a series of transition-metal-centered monocyclic boron wheel clusters M©B n ( n = 8–10) were reported by Wang and Boldyrev [ 36 ].…”

Planar Pentacoordinate Zinc Group Elements Stabilized by Multicentric Bonds

“…3,40−43 Recently, an all-metallic planar pentacoordinate Be center with σ-only aromaticity has been computationally proposed. 44 Although σ aromaticity has been the driving force for planar hypercoordinate transition metal atoms, 3,40−43 such reports of σ aromaticity for zinc group elements (Zn, Cd, Hg) showing a planar hypercoordinate geometry are rare. 43,45 Schleyer and co-workers reported the computational design of planar hepta-, octa-, nona-, and decacoordinate zinc center enclosed by boron rings.…”

“…The concept of σ aromaticity, first proposed to rationalize the apparent stability of cyclopropane, has been particularly valuable to understand the bonding and stability of all-metal aromatic and antiaromatic systems. − Even the dual σ + π aromaticity has been found to be responsible for the high stability of transition-metal-centered borometallic molecular wheels. ,− Recently, an all-metallic planar pentacoordinate Be center with σ-only aromaticity has been computationally proposed . Although σ aromaticity has been the driving force for planar hypercoordinate transition metal atoms, ,− such reports of σ aromaticity for zinc group elements (Zn, Cd, Hg) showing a planar hypercoordinate geometry are rare. , Schleyer and co-workers reported the computational design of planar hepta-, octa-, nona-, and decacoordinate zinc center enclosed by boron rings .…”