Ionic, Directional,and Collective Interaction Regimesin Doped B₁₂ Clusters: An IQA Perspective

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 exchange-correlation terms are significant and distributed over many boron atoms (ScB₁₂, TiB₁₂ and FeB₁₂), consistent with a more collective mode of interaction with the boron scaffold. The results provided herein offer a chemically transparent framework for the rational selection of dopants in boron-rich clusters by revealing how different elements promote distinct structural motifs and bonding regimes.