A photoelectron spectroscopy and ab initio study of the structures and chemical bonding of the B25− cluster

Abstract

Photoelectron spectroscopy and ab initio calculations are used to investigate the structures and chemical bonding of the B25(-) cluster. Global minimum searches reveal a dense potential energy landscape with 13 quasi-planar structures within 10 kcal/mol at the CCSD(T)/6-311+G(d) level of theory. Three quasi-planar isomers (I, II, and III) are lowest in energy and nearly degenerate at the CCSD(T) level of theory, with II and III being 0.8 and 0.9 kcal/mol higher, respectively, whereas at two density functional levels of theory isomer III is the lowest in energy (8.4 kcal/mol more stable than I at PBE0/6-311+G(2df) level). Comparison with experimental photoelectron spectroscopic data shows isomer II to be the major contributor while isomers I and III cannot be ruled out as minor contributors to the observed spectrum. Theoretical analyses reveal similar chemical bonding in I and II, both involving peripheral 2c-2e B-B σ-bonding and delocalized interior σ- and π-bonding. Isomer III has an interesting elongated ribbon-like structure with a π-bonding pattern analogous to those of dibenzopentalene. The high density of low-lying isomers indicates the complexity of the medium-sized boron clusters; the method dependency of predicting relative energies of the low-lying structures for B25(-) suggests the importance of comparison with experiment in determining the global minima of boron clusters at this size range. The appearance of many low-lying quasi-planar structures containing a hexagonal hole in B25(-) suggests the importance of this structural feature in maintaining planarity of larger boron clusters.

Understanding the Central Location of a Hexagonal Hole in a B36 Cluster

“…However, the upper limit for the B n − anionic clusters still remains an open question. Anionic clusters up to B 25 − were confirmed to be planar . Beyond the B 25 − cluster, the B 28 − and B 30 − clusters are all 2D boron sheets .…”

“…[5] However,t he upper limit for the B n À anionic clusters still remains an open question.A nionic clusters up to B 25 À were confirmed to be planar. [15] Beyond the B 25 À cluster, the B 28 À and B 30 À clusters are all 2D boron sheets. [16,17] The biggest planar boron cluster with an egative chargef ound so far has 40 boron atoms.…”

Valence bonds in elongated boron clusters

“…For this, we chose the particular family of the so‐called elongated boron clusters. The aim is to obtain a set of rules that rationalize the electronic structure calculations on a series of structures extending from to …”

Nature of Bonding in Bowl‐Like B36 Cluster Revisited: Concentric (6π+18π) Double Aromaticity and Reason for the Preference of a Hexagonal Hole in a Central Location

“…[19] Structures I-III differ only in the positiono ft he hexagonal hole:a tt he centero ft he first boron ring in I,o nt he first boron ring in II,a nd on the second boron ring in III.A sa result,t he inner BDR ribbon in II is not closed, owing to a defect, and yet it also has af illed andi mperfect "disk" center. [39,40] In contrast, neither the inner nor outer BDR ribbonsi nIII are closed, owing to the defect, although it has ap erfect hexacoordinate B 7 disk at the center. [39,40] In contrast, neither the inner nor outer BDR ribbonsi nIII are closed, owing to the defect, although it has ap erfect hexacoordinate B 7 disk at the center.…”

“…Notably,s imilarp entacoordinate boron motifsw ere previously observed in B 24 À and B 25 À clusters. [39,40] In contrast, neither the inner nor outer BDR ribbonsi nIII are closed, owing to the defect, although it has ap erfect hexacoordinate B 7 disk at the center.…”