Toward Two-Dimensional Superatomic Honeycomb Structures. Evaluation of [Ge9(Si(SiMe3))3]- as Source of Ge9-Cluster Building Blocks for Extended Materials

Inspired by recent experimental realizations of two-dimensional (2D) metals and alloys, we theoretically investigate plausible formation of new germanium frameworks based on the aggregation of ligand-decorated Ge-9 clusters. Here, we explore the formation of single-, double-, and triply connected arrays of species with Zintl-ion core of Ge9 leading to the formation of dimers ([Ge9R2](2)(2)), hexamers ([Ge9R](6)(6)), and two-dimensional arrays ([M-3{Ge-9}(3)](infinity); M = Li, Cs). This can be potentially addressed by the controlled removal of ligands from the [Ge-9{Si(SiMe3)(3)}(3)](-) monoanion acting as the source of Ge-9 building blocks. Our results reveal that the bonding between different Ge-9 cores is favorable and covalent in nature as a localized 2c2e GeGe exobond. The extended two-dimensional {Ge9}(infinity) array designed as [M3{Ge9}3](infinity) with M = Li, Cs in periodic boundary conditions is energetically stable. The resulting layered Ge-structure has similar stability as that of germanene. It exhibits large pores with radius of 5.23 angstrom between the three-connected Ge9 clusters. Hence, it can be considered as a the first superatomic honeycomb structure proposed to date. This 2D material exhibit a small band gap in contrast to the 2D germanene which has no such gap. Hence, the two-dimensional Ge9 cluster-based compound would have potential for a tunable bandgap material. The use of Ge-clusters is suggested as an interesting approach to obtain nanomaterials accessing to novel alleotropes.