Gas-Phase Stability of Derivatives of the closo-Hexaborate Dianion B₆H₆^2-

Abstract

B(6)H(6)(2-) does not represent a stable gas-phase dianion, but emits spontaneously one of its excess electrons in the gas phase. In this work we address the question whether small stable gas-phase dianions can be constructed from the parent B(6)H(6)(2-) dianion by substitution of the hydrogens with appropriate ligands. Various hexa-, tetra-, and disubstituted derivatives B(6)L(6)(2-), B(6)H(2)L(4)(2-), and B(6)H(4)L(2)(2-) (L = F, Cl, CN, NC, or BO) are investigated with ab initio methods in detail. Four stable hexasubstituted B(6)L(6)(2-) (L = Cl, CN, NC, or BO) and three stable B(6)H(2)L(4)(2-) (L = CN, NC, or BO) gas-phase dianions could be identified and predicted to be observable in the gas phase. The trends in the electron-detachment energies depending on various ligands are discussed and understood in the underlying electrostatic pattern and the electronegativities of the involved elements.

From an Icosahedron to a Plane: Flattening Dodecaiodo‐dodecaborate by Successive Stripping of Iodine

“…This finding is in accordance with calculations showing that B 12 H 12 2− is the smallest electronically stable hydro‐ closo ‐dodecaborate cluster 13. B 6 X 6 2− has been shown by calculations to be unstable to electron loss with X=H, but stable with X=Cl 14. Thus, the general pattern of fragmentation observed herein for B 12 I 12 2− , loss of neutral atoms and ions but not loss of electrons, agrees with previous calculations.…”

Dianionic Tetraborates Do Exist as Stable Entities

“…The B-B distance within the B 4 tetrahedron in all isomers has a value of around 1.69 Å (Table 1), which is slightly shorter than the values found for the B-B bond in B 6 (CN) 6 2-(1.72 Å). 20 The cage ligand bonds are clearly single bonds with typical values for the three examined dianions. The C-N bond of B 4 (CN) 4 2-and the N-C bond of B 4 (NC) 4 2-have lengths typical for triple bonds, whereas the B-O bond of B 4 (BO) 4 2-has more double bond character.…”

“…18 In contrast, the small members of the hydro-closoborates B n H n 2-(n < 12) are not stable in the gas phase but spontaneously emit one of their excess electrons. 19,20 The smallest hydro-closo-borate that is stable in the gas phase is B 12 H 12 2-. 19 This is not surprising because it is well-known that most of the small multiply charged anions known from condensed phases, such as carbonate CO 3 2-, 21-23 sulfate SO 4 2-, [24][25][26] and phosphate PO 4 3-, 24 are not stable in the gas phase owing to the strong electrostatic repulsion of the excess negative charges.…”

“…20 Indeed, it could be shown by means of standard ab initio methods that the dianions B 6 (CN) 6 2-, B 6 (NC) 6 2-, and B 6 (BO) 6 2-and the tetra-substituted isomers represent stable gas-phase dianions and should thus be observable in mass spectrometric experiments. 20 Motivated by these findings, we reduced the size of the substituted closo-borates and studied the stability of the penta-and tetraborate dianions B 5 X 5 2-and B 4 X 4 2-(X ) CN, NC, or BO). 33 All of these systems represent stable gas-phase dianions, although they are not yet known to exist either in solution or crystals or in the gas phase.…”

Substituent‐Stabilized Organic Dianions in the Gas Phase and Their Potential Use as Electrolytes in Lithium‐Ion Batteries

“…Over a decade ago, Zint et al. studied the stability of B 6 H 6 2− by substituting the H atoms with groups such as F, Cl, CN, NC or BO, which resulted in stable dianions in the gas phase . Similar studies have also been performed for the penta‐ and tetraborate dianions B 5 X 5 2− and B 4 X 4 2− .…”