The closoborane and their derivatives have attracted high interest due to their superionic conductivity. Very recently, high ionic conductivities have been reported for compounds containing the closoborane ion B12H12 2−. In this work, we address halogen-substituted ions B12HnX(12−n) 2− (n = 0−3, 6, 9−12 and X = F, Cl, Br) using DFT calculations to probe the structures, the chemical stability, and the electrochemical stability, as well as spectroscopic properties in view of potential future applications. Considering the theoretical reaction n/12 B12H12 2− + (12−n)/12 B12X12 2− → B12HnX(12−n) 2−, it appears that for X = Cl and Br the compounds with n = 6 are stabilized by about 100 kJ/mol. The calculation of the vertical detachment energy (which is indirectly related to the electrochemical stability) shows an increasing stability with increasing halogen content. These results suggest that, for practical applications, it is likely that a partially halogenated ion offers the best compromise. The calculations of vibrational properties and NMR chemical shifts also reveal several systematic trends, which are discussed and compared to available literature values.