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 pi-delocalization in Ge-3(NH)(3), which models germanazene that was prepared by Power et al. To get a broader perspective, we explore the entire E-3(NH)(3) series (E=C, Si, Ge, Sn, Pb). Thus, while (4n+ 2)pi systems of carbon rings are aromatic with cyclic pi-delocalization, the E-3(NH)(3) rings are dominated by a nonbonded structure, wherein pi-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 E-3(NH)(3) creates pi-systems, which are stabilized by charge-shift bonding. Thus, unlike in benzene, in Ge-3(NH)(3) delocalization of pi-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, Ge-3(NAr)(3) (Ar=Ph).