Double aromaticity in a BBe₆H₆⁺cluster with a planar hexacoordinate boron structure

Abstract

Aromaticity is one of the central concept in chemisty which leads to the stability of many cluseters with interesting structural motiff. Herein, a cationic BBe6H6 cluster featuring a planar hexacoordinate...

σ-Aromaticity Planar Pentacoordinate Beryllium Atoms

“…The rule-breaking bonding usually requiring new considerations upon classical bonding models, especially an effective electronic design scheme, is a key issue to excavate them. − The highly delocalized bonding originating from the active participation of p/d π electrons of the central atom has been proven to facilitate planar hypercoordinate main-group/transition metals. − For instance, the fully delocalized π electrons of the central p z lone pair reinforced by π-acceptor/σ-donor ligands can effectively stabilize the high-symmetry planar hypercoordinate carbon or other main-group atoms, making the mixed π/σ-aromatic species according to the 4 n + 2 rule. − The dual σ + π aromaticity is responsible for highly stable transition-metal-centered borometallic molecular wheels. ,− It is worth noting that the σ aromaticity alone has been found to provide a crucial electronic stabilization factor for planar hypercoordinate clusters, but it is limited to transition metals. − …”

“…The valence population of ppBe is given in Table S1, and the negligible p z occupations of the ppBe and M atoms in BeM 5 + are clearly different from those of π-delocalized planar hypercoordinate species, − ,− where the high p z occupations originating from the effective p z lone-pair π electrons of the central atoms are of importance electronically to support their stability and planarity. The high s occupations of the ppBe and M atoms, and the considerable p x and p y occupations of the ppBe atom both reveal that the pronounced σ delocalization rather than π delocalization is a main bonding picture in BeM 5 + .…”

Planar hexacoordinate gallium

“…61 The planar hexacoordinate boron that is relevant to the present study is the most stable isomer of BBe 6 H 6 + with a phB center and having dual (+) aromaticity. 26,27 Cluster containing a phAl in the global minimum form of Al 4 C 6 cluster was also reported. 62 Apart from them, planar hexacoordination in an isolated cluster was not found.…”

CAl4Mg0/−: Global Minima with a Planar Tetracoordinate Carbon Atom

“…Since then, many molecules containing ptC have been characterized in silico [23][24][25][26][27][28][29][30][31][32], and some have been experimentally detected [1][2][3][4][5][6][7][8][9]. Lately, the idea of ptC has been extended to planar hypercoordinate carbon (phC; penta [33][34][35] and hexa [36][37][38][39][40] coordination) as well as to other elements such as B [41,42] or N [43] considering their potential applications in material science [44,45].…”