Theoretical studies on doubly and triply linked polymers of Ge9 clusters

Experimental isolation of singly-bonded polymers of Ge9, Sn9 clusters and oligomers of doubly linked Ge9 clusters encouraged us to explore other possibilities of polymerizing Ge9 units. The electron counts in the reported oligomers are not consistent with simple ideas of localized intercluster bonding; demanding a detailed theoretical analysis. Band structure calculations suggest delocalized bonding with a charge requirement of 2− per Ge9 unit for all polymeric doubly linked chains. DFT-based geometry optimization of model doubly linked polymers shows that one of the two possible forms is stable and has a band gap of ≈1.0 eV. A detailed bonding analysis of a theoretical model, Rb4Ge18, shows that the increased inter-polyhedral bond weakens the intra-polyhedral bonding. Ternary fusions are found to be generally unstable – for triple linkages the intrapolyhedral bonding is still further reduced; the polymers appear to be unstable towards dissociation into individual Ge9 units.