[Ag(Sn9-Sn9)]5- and [(η4-Sn9)Ag(η1-Sn9)]7-, as aggregates of spherical aromatic building blocks. Persistence of aromaticity upon cluster gathering

Formation of cluster-based materials requires a fundamental understanding of the resulting cluster aggregation processes. The Sn94- Zintl-ion structure can be viewed as a building block featuring a spherical aromatic species, leading to a cluster gathering upon oxidative coupling and/or mediated by transition metals. Here, we evaluate the spherical aromatic properties of [Sn9-Sn9]6-, [Ag(Sn9-Sn9)]5- and [(η4-Sn9)Ag(η1-Sn9)]7-, as aggregates of two Sn9 building units held together via oxidative coupling and mediated by a Ag(I) transition metal center. Our results from magnetic criteria of aromaticity show that the inherent spherical aromatic characteristics of the parent Sn94- cluster are persistent in the overall aggregate where the enabled shielding cones ascribed to each Sn9 unit are able to interplay between them, leading to an overlap of the shielding regions. Hence, the two approaches for bringing cluster units together are able to retain the inherent spherical aromatic features for each Sn9 unit, leading to a cluster-based dimer where the parent properties remain. Thus, further cluster-based materials can be envisaged from aggregation upon oxidative coupling and/or mediated by transition metals, where the constituent building blocks retain their initial features, useful to guide the formation of more complex cluster-based aggregates.

Ligand-free supermolecules: [Pd2@Ge18]4- and [Pd2@Sn18]4- as multiple-bonded Zintl-ion clusters based on Pd@Ge9 and Pd@Sn9 assembled units

Understanding intercluster bonding interactions is important in the rational synthesis of building blocks for molecular materials. Such characteristics have been developed for coinage metal clusters resembling single-, double-, and triple-bonded species, coined as supermolecules. Herein, we extend such an approach for understanding main-group clusters, thus evaluating [Pd2@E18]4- clusters (E = Ge, Sn) involving the fusion of parent spherical aromatic [Pd@E12]2- building units. Our results indicate intercluster bonding provided by contribution from 2P and 1G shells centered at each building motif, leading to an overall bond order of 2.70 and 2.31 for [Pd2@Ge18]4- and [Pd2@Sn18]4-, respectively. In addition, 119Sn-NMR patterns were evaluated to complement the experimental characterization of a single peak owing to the insolution fluxional behavior of [Pd2@Sn18]4- as three peaks owing to the three sets of unique Sn atoms within the structure. Magnetic response properties revealed that spherical aromatic characteristics from parent [Pd@E12]2- building units are retained in the overall [Pd2@E18]4- oblate cluster as two spherical aromatic units. Hence, the notion of superatomic molecules is extended to Zintl-ion clusters, favoring further rationalization for the fabrication of cluster-assembled solids.