Stability of B₁₂(CN)₁₂²⁻: Implications for Lithium and Magnesium Ion Batteries

Abstract

Multiply charged negative ions are seldom stable in the gas phase. Electrostatic repulsion leads either to autodetachment of electrons or fragmentation of the parent ion. With a binding energy of the second electron at 0.9 eV, B12H122− is a classic example of a stable dianion. It is shown here that ligand substitution can lead to unusually stable multiply charged anions. For example, dodecacyanododecaborate, B12(CN)122−, created by substituting H by CN is found to be highly stable with the second electron bound by 5.3 eV, which is six times larger than that in the B12H122−. Equally important is the observation that CB11(CN)122−, which contains one electron more than needed to satisfy the Wade‐Mingos rule, is also stable with its second electron bound by 1.1 eV, while CB11H122− is unstable. The ability to stabilize multiply charged anions in the gas phase by ligand manipulation opens a new door for multiply charged species with potential applications as halogen‐free electrolytes in ion batteries.

B12(SCN)12–: An Ultrastable Weakly Coordinating Dianion

“…When one of the B atoms in the B 12 (CN) 12 is replaced by C, ΔE 1 of CB 11 (CN) 12 is 8.72 eV which is also much larger than that of CB 11 H 12 . More importantly, the second electron in CB 11 (CN) 12 2− is bound by 1.07 eV, while the CB 11 H 12 2− dianion is unstable compared to its monoanion state. It was further found that the binding energies of Mg 2+ and Li + to CB 11 (CN) 12 2− and CB 11 (CN) 12 − , respectively, are also significantly lower than those bound to CB 11 H 12 2− and CB 11 H 12 − .…”

“…It was further found that the binding energies of Mg 2+ and Li + to CB 11 (CN) 12 2− and CB 11 (CN) 12 − , respectively, are also significantly lower than those bound to CB 11 H 12 2− and CB 11 H 12 − . All these properties indicate that B 12 (CN) 12 2− and CB 11 (CN) 12 − might serve as the anionic components of electrolytes inside metal-ion-based batteries. However, the cyanide ion CN − is highly toxic which will make it difficult to synthesize B 12 (CN) 12 2− in experiment.…”

“…More importantly, the second electron in CB 11 (CN) 12 2− is bound by 1.07 eV, while the CB 11 H 12 2− dianion is unstable compared to its monoanion state. It was further found that the binding energies of Mg 2+ and Li + to CB 11 (CN) 12 2− and CB 11 (CN) 12 − , respectively, are also significantly lower than those bound to CB 11 H 12 2− and CB 11 H 12 − . All these properties indicate that B 12 (CN) 12 2− and CB 11 (CN) 12 − might serve as the anionic components of electrolytes inside metal-ion-based batteries.…”

“…Using density functional theory, they calculated the binding energies of the first (ΔE 1 ) and second (ΔE 2 ) electrons. Known as electron affinities, these are defined, respectively, as It was shown that the second electron in B 12 (CN) 12 2− is bound by ΔE 2 = 5.3 eV which is about six times larger than the corresponding value of 0.9 eV in the well-known closo-borane 12 2− , 8.6 eV, is also much larger than the corresponding 4.6 eV binding energy in B 12 H 12 2− . When one of the B atoms in the B 12 (CN) 12 is replaced by C, ΔE 1 of CB 11 (CN) 12 is 8.72 eV which is also much larger than that of CB 11 H 12 .…”

“…Known as electron affinities, these are defined, respectively, as It was shown that the second electron in B 12 (CN) 12 2− is bound by ΔE 2 = 5.3 eV which is about six times larger than the corresponding value of 0.9 eV in the well-known closo-borane 12 2− , 8.6 eV, is also much larger than the corresponding 4.6 eV binding energy in B 12 H 12 2− . When one of the B atoms in the B 12 (CN) 12 is replaced by C, ΔE 1 of CB 11 (CN) 12 is 8.72 eV which is also much larger than that of CB 11 H 12 . More importantly, the second electron in CB 11 (CN) 12 2− is bound by 1.07 eV, while the CB 11 H 12 2− dianion is unstable compared to its monoanion state.…”