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

Abstract

Using density functional theory and a hybrid exchange-correlation functional, a systematic study of the stability and electronic structure of neutral and multiply charged organic molecules, B C X (n=0, 1, 2; X=H, F, CN) and B C X (n=0, 1; X=H, F, CN) is performed. The results show that in addition to the aromaticity of the molecules, substituents play an important role in stabilizing the organic dianion complexes. In particular, it is demonstrated that CN groups are responsible for the stability of organic dianions as it has recently been found to be the case in B-cage compounds such as B (CN) and CB (CN) . It is also shown that the stable organic dianions B C (CN) and BC (CN) might be halogen-free electrolytes in Li-ion batteries.

Rational Design of Stable Dianions by Functionalizing Polycyclic Aromatic Hydrocarbons

“…The stability of the dianion is further enhanced if such substitution is accompanied by substitution of C by B. Note that the dianion B 2 C 4 (CN) 6 is stable against electron emission by 1.10 eV . The second electron affinity of B 2 C 8 (CN) 8 (1.97 eV) is larger than that of B 2 C 4 (CN) 6 as it has more CN ligands.…”

“…Note that the dianion B 2 C 4 (CN) 6 is stable against electron emission by 1.10 eV. [15] The second electron affinity of B 2 C 8 (CN) 8 (1.97 eV) is larger than that of B 2 C 4 (CN) 6 as it has more CN ligands. Thus, one can use both ligand substitution and size as effective parameters to enhance the stability of multiply negatively charged organic molecules.…”

“…The role of substituents in enhancing the stability of multiply changed molecules in the gas phase has also been studied by replacing H atoms in B 4 H 4 2− and B 6 H 6 2− by F, Cl, CN or BO . Thus, the replacement of core and ligand atoms can not only transform organic molecules with negative electron affinities into superhalogens, but also enable small dianions to be stable in the gas phase …”

“…[13,14] Thus, the replacemento fc ore and ligand atoms can not only transform organic moleculesw ith negative electron affinities into superhalogens, but also enables mall dianions to be stable in the gas phase. [15,16] In this paper,w ef ocus on polycyclic aromatic hydrocarbons to determine if the above scheme indeed can succeed in creating organic dianions. We address three questions:F irst, can one transform naphthalene (C 10 H 8 )t oastable dianion by replacing the Ca toms in the core rings with Ba toms and the H atoms with Fo rC N?…”

Rational Design of Stable Dianions and the Concept of Super-Chalcogens

“…Among the most well-known dianions is B 12 H 12 2– closo -borane, , which is stable, in the gas phase, against spontaneous electron emission by 0.9 eV. Stability of these species is explained by the Wade–Mingos rule, which requires ( n + 1) pairs of electrons, where n is the number of vertices in the boron polyhedron. − It was recently shown that the stability of these dianions could be substantially improved by ligand substitution. − For example, B 12 (CN) 12 2– and B 12 (SCN) 12 2– are stable against electron emission by 5.3 and 3.3 eV, , respectively. This prediction has recently been confirmed experimentally and the measured second electron affinity of B 12 (CN) 12 2– , 5.55 eV, agrees well with the predicted value.…”