Ionic, Directional, and Collective Interaction Regimes in 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.