Fluxional Bonds in Planar B₁₉⁻, Tubular Ta@B₂₀⁻, and Cage‐Like B₃₉⁻

Abstract

Based on detailed bonding analyses on the fluxional behaviors of planar B 19 − , tubular Ta@B 20 − , and cage-like B 39 − , we propose the concept of fluxional bonds in boron nanoclusters as an extension of the classical localized bonds and delocalized bonds in chemistry.Figure 3. (a) The four true minima (C 3 , C 2 , M 1 ,and M 2 ) of B 39 − and three transition states (TS 1 , TS 2 , and TS 3 ) between them, with their energies relative to the global minimum C 3 B 39 − indicated in kcal/mol. [23] The active B 5 W, X, and M sites in the front of the cages are highlighted in blue. (b) W-X-M transformation of borospherenes, with the 3c-2e σ bonds and 5c-2e σ bond highlighted in the W-, X-, and M-shaped B 5 units. [Color figure can be viewed at wileyonlinelibrary.com] [Color figure can be viewed at wileyonlinelibrary.com] WWW.C-CHEM.ORG

Probing the Fluxional Bonding Nature of Rapid Cope rearrangements in Bullvalene C10H10 and Its Analogs C8H8, C9H10, and C8BH9

“…Such energy barriers appear to be much higher than that previously reported in boron nanoclusters 1–4 . This can be qualitatively understood based on the fact that, due to its prototypical electron-deficiency, boron has the strong propensity to form delocalized σ and π bonds in highly reactive boron nanoclusters with extremely small energy barriers 1–4 , while the fluxional processes in 1 , 4 , 7 , and 10 possess much higher energy barriers because they involve the formations and breakages of C-C interactions in stable organic species. The C1-C2 single bond with r c1-c2 = 1.53~1.59 Å on the top in the C 3v or C s GSs has been elongated to r c1–c2 = r c5–c6 = 1.92~2.04 Å in the C 2v TSs.…”

“…Classical bonds include localized two-center-two-electron (2c-2e) bonds and delocalized multi-center-two-electron (mc-2e, m ≥ 3) bonds. Our group predicted the existence of fluxional σ- and π-bonds (FBs) in planar B 18 2− and B 19 − , half-sandwich KB 18 − , tubular Ta@B 20 − , Ta@B 21 , and Ta@B 22 + , and cage-like B 39 − in four recent papers 1–4 . Multicenter FBs in these fluctuating boron nanoclusters form and break constantly in concerted mechanisms at room temperatures.…”

“…Detailed bonding analyses were performed on the concerned species using the adaptive natural density partitioning (AdNDP) 25–27 method. The AdNDP approach recovers both the localized and delocalized bonding elements of the concerned systems and has been successfully applied to a wide range of nanoclusters and molecules 1–4,28–38 . Natural bonding orbital (NBO) analyses were performed utilizing the NBO 6.0 program 39 .…”

From inverse sandwich Ta2B7+ and Ta2B8 to spherical trihedral Ta3B12−: prediction of the smallest metallo-borospherene

“…PE measurements and infrared photodissociation (IR-PD) spectra in combination with rst-principles theory calculations have proven to be powerful approaches in characterizing novel clusters in gas phases. [3][4][5][6][7][17][18][19][20][21][22][23][24][25][26][27][28]62 As shown in Fig. 4, the highsymmetry Ta 3 B 12 À (3) exhibits relatively simple IR and Raman spectral patterns, with the major IR active peaks at 507 (e 0 ), 559 (e 0 ), 668 ða 00 2 Þ, and 881 (e 0 ) cm À1 (Fig.…”

“…behaving like a tubular molecular rotor at 900 K facilitated by prototypical multicentre uxional bonds (FBs) which form and break constantly. 24 A series of perfect di-metaldoped inverse sandwich complexes have also been observed in PE experiments, including D 6h Ta 2 B 34 with more than 2000 singlet or triplet stationary points explored for each cluster at PBE/DZVP level. 35 Low-lying isomers were then fully optimized at the PBE0 (36) level with the 6-311+G* basis set 37 for B and Stuttgart relativistic small-core pseudopotential 38,39 for Ta using the Gaussian 16 program suite, 40 with vibrational frequencies checked to make sure that all isomers reported are true minima.…”