We present an experimental and computational study of the oligomerization in icosahedral closo-(car)boranes Li2[B12H12] (I) and Li[CB11H12] (II). The experiments were performed on a hybrid ESI-TQ-FT-ICR mass spectrometer equipped with a 7.0 T superconducting magnet. The computational study consisted of finding energy minimum structures for the molecules I, II and the derived anions [B 12H12]2-, [CB11H12] -, [I2-Li]-, and [II2-Li] -, as well as an estimate for the dissociation energy in the processes [X2-Li]- → X + [X-Li]- with X = I, II. Comparison of experiments and computations shows an excellent agreement for the bond dissociation energy in the process [II2-Li]- → II + [II-Li]- with ΔE = 1.5 eV. © 2012 American Chemical Society.