Thermochemical Properties and Electronic Structure of Boron Oxides B_nO_m (n = 5−10, m = 1−2) and Their Anions

Abstract

The molecular and electronic structures of a series of small boron monoxide and dioxide clusters B(n)O(m) (n = 5-10, m = 1, 2) plus their anions were predicted. The enthalpies of formation (DeltaH(f)'s), electron affinities (EAs), vertical detachment energies, and energies of different fragmentation processes are predicted using the G3B3 method. The G3B3 results were benchmarked with respect to more accurate CCSD(T)/CBS values for n = 1-4 with average deviations of +/-1.5 kcal/mol for DeltaH(f)'s and +/-0.03 eV for EAs. The results extend previous observations on the growth mechanism for boron oxide clusters: (i) The low spin electronic state is consistently favored. (ii) The most stable structure of a neutral boron monoxide B(n)O is obtained either by condensing O on a BB edge of a B(n) cycle, or by binding one BO group to a B(n-1) ring. The balance between both factors is dependent on the inherent stability of the boron cycles. (iii) A boron dioxide is formed by incorporating the second O atom into the corresponding monoxide to form BO bonds. (iv) A B(n)O(m)(-) anion is constructed with BO groups bound to the B(n-1) or B(n-2) rings (yielding the B(n-2)(BO)(2)(-) species). This becomes the preferred geometry for the larger boron dioxides, even in the neutral state. The boronyl group mainly behaves as an electron-withdrawing substituent reducing the binding energy and resonance energy of the oxides. (v) The boron oxides conserve some of the properties of the parent boron clusters such as the planarity and multiple aromaticity.

Thermochemical properties, electronic structure and bonding of mixed lithium boron clusters (BnLi, n=1–8) and their anions

“…During the past decades, a large number of investigations have been reported on the global minima, chemical bonding nature [1][2][3][4][5][6][7][8][9], spectroscopic properties [10][11][12][13][14][15] and thermochemical parameters [16][17][18] of the small bare boron clusters B n (n = [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] in the neutral, cationic and anionic states. It was pointed out that these small boron clusters strongly prefer a planar shape [6,10,11] and the three-dimensional geometries become favored only from the clusters containing more than 20 atoms.…”

“…It was pointed out that these small boron clusters strongly prefer a planar shape [6,10,11] and the three-dimensional geometries become favored only from the clusters containing more than 20 atoms. Furthermore, most of the small bare boron clusters can be considered as r-aromatic, p-aromatic or doubly (p and r) aromatic species, that are in line with their high stability and planarity [6,10,11,[17][18][19][20].…”

“…Recently, we reinvestigated the electronic structure, thermochemical parameters and growth mechanisms of the small B n clusters, their monoxides and dioxides, B n O m , with n = 1-13 and m = 1-2, together with their anions [16][17][18]. To evaluate the molecular stability, we employed the resonance energy (RE) index, that was defined earlier by Dewar and deLlano [26a] and recently updated by Dixon and co-workers [26b].…”

“…To evaluate the molecular stability, we employed the resonance energy (RE) index, that was defined earlier by Dewar and deLlano [26a] and recently updated by Dixon and co-workers [26b]. In addition, we defined the normalized resonance energy (NRE), which is a simple index to quantify the cluster stability [18]. The most typical feature of B n O m species is the strength of the BO bond.…”

“…The BO group mainly behaves as an electron-withdrawing substituent reducing the binding energy and resonance energy of the oxides. Overall, the latter conserve the planarity and multiple aromaticity of the parent boron clusters [18]. Considering oxygen as an electronegative element, the effects of lithium, which is a 0301-0104/$ -see front matter Ó 2010 Elsevier B.V. All rights reserved.…”