Multiple local σ-aromaticity of nonagermanide clusters

Nonagermanide clusters are widely used in inorganic synthesis and are actively studied by experimentalists and theoreticians. However, chemical bonding of such versatile species is still not completely understood. In our work we deciphered a bonding pattern for various experimentally obtained nonagermanide species. We localized the electron density via the AdNDP algorithm for the model structures ([Ge(9)](4–), [Ge(9){P(NH(2))(2)}(3)](–), Cu[Ge(9){P(NH(2))(2)}(3)] and Cu(NHC)[Ge(9){P(NH(2))(2)}(3)]) and obtained a simple and chemically intuitive bonding pattern which can explain the variety of active sites and the existence of both D(3h) and C(4v) geometries for such clusters. Moreover, the [Ge(9)](4–) core is found to be a unique example of an inorganic Zintl cluster with multiple local σ-aromaticity.