B12H122− can be formed during the thermal decomposition of metal borohydrides (M(BH4)x). Halogen ions such as fluoride or chloride can contribute to destabilize the BH4− ions. Hydride and fluoride mixed species like B12HnF(12−n)2− will be probable products after hydrogen release from mixed boro-hydride-fluoride (BHxF(4−x)−) or borohydride-borofluoride systems (BH4−, BF4−). Various number of isomers are possible for B12HnF(12−n)2− (n = 2–11). DFT calculations were performed on isolated ions of all the possible isomers for (n = 0–3, 9–12), using B3LYP functionals and 6-31G(d,p) basis set. Relative stability, vibrational and NMR spectroscopy of these isomers are discussed and compared with available experimental data.