Coaxial Triple‐Layered versus Helical Be₆B₁₁⁻ Clusters: Dual Structural Fluxionality and Multifold Aromaticity

Abstract

Tw olow-lying structures are unveiled for the Be 6 B 11 À nanocluster system that are virtually isoenergetic.T he first, triple-layered cluster has aperipheral B 11 ring as central layer, being sandwiched by two Be 3 rings in acoaxial fashion, albeit with no discernible interlayer BeÀBe bonding.T he B 11 ring revolves like aflexible chain even at room temperature,gliding freely around the Be 6 prism. At elevated temperatures (1000 K), the Be 6 core itself also rotates;t hat is,t wo Be 3 rings undergo relative rotation or twisting with respect to each other. Bonding analyses suggest four-fold (p and s)a romaticity, offering adilute and fluxional electron cloud that lubricates the dynamics.The second, helix-type cluster contains aB 11 helical skeleton encompassing adistorted Be 6 prism. It is chiral and is the first nanosystem with ab oron helix. Molecular dynamics also shows that at high temperature the helix cluster readily converts into the triple-layered one.

Fluxional Boron Clusters: From Theory to Reality

“…Most recently, some of us, in collaboration with the group of Zhai, reported an unprecedented multifold fluxionality in Be 6 B 11 − . 74 The computations indicate that Be 6 B 11 − exhibits two nearly isoenergetic global minimum-energy structures: a helix-type C 2 -symmetric cluster and a coaxial multiple-layered C 2v -symmetric system (see Figure 12).…”

Effects of Temperature on Enantiomerization Energy and Distribution of Isomers in the Chiral Cu13 Cluster

“…Moreover, the calculated total energy of the cluster demands a high level of quantum mechanical methodology to produce reliable energies. Despite that, several algorithms coupled with DFT have been employed to search for the lowest energy structures on the potential energy surface of atomic clusters, such as the kick methodology [65][66][67][68][69][70][71][72][73][74][75][76][77] and genetic algorithms [43,[78][79][80][81]. Our computational procedure to elucidate the lowest energy consisted of a hybrid genetic algorithm called GALGOSON [43,47].…”

Boron Teetotum: Metallic [Ti(B6CxNy)]q and Bimetallic [Ti2(B6CxNy)]q Nine-Membered Heterocycles with x + y = 3 and −1 ≤ q ≤ 3

“…Previous investigations indicated that sp hybridization and multiple aromaticity tend to govern the planar shape for small boron clusters. , The π aromaticity of the planar pure boron ring obeys the classical electron counting rule 4 N + 2, whereas polycyclic structures such as B 18 2– , B 19 – , and B 20 2– and related clusters are classified as disk aromatic species. − The bowl-shaped boron B 30 cluster is identified as a typical nonconventional structure which has a pentagonal hole and satisfies a motif of B n @B 2 n @B 3 n with n = 5 . Subsequent studies demonstrated that the B 32 , B 35 , B 36 , and, more recently, B 50 clusters are also considered as members of bowl-shaped clusters which contain a hexagonal and heptagonal hole. − The tubular motif of the structure in which B m strings are connected together in antiprism fashion, was observed for boron clusters such as B 20 (double ring), B 27 + , and B 42 (both being triple ring). ,, The tubular shape emphasizes the rich perspective of electron distribution of boron clusters as it presents a tubular aromaticity which can be rationalized by the models of electron in cylinder and hollow cylinder. , Interestingly, fullerene-like structures are also identified for boron clusters including the B 40 , B 42 + , B 44 , and B 46 that contain large heptagonal, octagonal, and nonagonal holes. − …”