Stability of B12 (CN)12 (2-) : Implications for Lithium and Magnesium Ion Batteries.

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, B12 H12 (2-) 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)12 (2-) , 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 B12 H12 (2-) . Equally important is the observation that CB11 (CN)12 (2-) , 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 CB11 H12 (2-) 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.