Dichotomy of Delocalization/Localization and Charge-Shift Bonding in Germanazene and its Heavier Group 14 Analogues: a Valence Bond Study

We present here a valence bond analysis of structure and π-delocalization in Ge₃(NH)₃, which models germanazene that was prepared by Power et al. To get a broader perspective, we explore the entire E₃(NH)₃ series (E=C, Si, Ge, Sn, Pb). Thus, while (4n+2)π systems of carbon rings are aromatic with cyclic π-delocalization, the E₃(NH)₃ rings are dominated by a nonbonded structure, wherein π-lone pairs are localized on the N atoms. Nevertheless, these molecules enjoy large covalent-ionic resonance energies of 153.0, 86.6, 74.2, 61.2, and 58.9 kcal/mol, respectively, for E=C, Si, Ge, Sn, Pb. The covalent-ionic mixing in E₃(NH)₃ creates π-systems, which are stabilized by charge-shift bonding. Thus, unlike in benzene, in Ge₃(NH)₃ delocalization of π-electron pairs of the N atoms is primarily confined to the domains of their adjacent Ge atoms. These features carry over to the substituted germanazene, Ge₃(NAr)₃ (Ar=Ph).