Abstract Doping can alter boron clusters in strikingly different ways, ranging from weak ionic stabilization to strongly localized and delocalized covalent bonding. Yet, these interaction modes are often discussed on a case-by-case basis, without a systematic comparative framework. Thus, we examined structural distortions, charge redistributions, electron sharing, and ionic and covalent contributions in a series of doped B12 clusters MB12 (M = Li, K, Be, Ca, Sc, Ti, Fe, Cu, Zn, Al, P) using the QTAIM and IQA methods of wave function analysis. These electron-deficient clusters reflect a balance between the energetic cost of deforming the B12 scaffold and the stabilizing interaction established with the heteroatom. Four broad interaction classes can be identified concerning individual M–B contacts: weak ionic contacts (LiB12 and KB12), strongly classical contacts (BeB12, CaB12 and AlB12), strongly covalent contacts (CuB12, ZnB12 and PB12), and a mixed regime in which both classical and e