Stable Unsaturated Silicon Clusters (Siliconoids)

• Applicant: Professor Dr. David Scheschkewitz
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 236324090

Unsaturated silicon clusters (siliconoids) are intermediates of the deposition of silicon from the gas phase. Stable derivatives of these ephemeral species are thought to occur embedded in amorphous silicon. In molecular form they are kinetically stabilized by the presence of sterically demanding substituents. Of particular note is the Si6R6 derivative with two unsubstituted vertices, which constitutes the global minimum structure and therefore the energetic silicon analogue of benzene. This pronounced preference prompted us to introduce an unambiguous trivial name for this new class of compounds: benzpolarene.The central objective is the functionalization of siliconoids including the incorporation of heteroelements such as the classical dopants for bulk silicon (boron and phosphorus), but also other Group 14 elements and transition metals. Suitable functionalities will allow for deliberately choosing from two possible options as a function of the targeted properties: either the expansion of the cluster core or the attachment of the desired element in the periphery of siliconoids. We aim to establish a comprehensive toolbox of such species in variable sizes that will enable us to tether the appropriate homo- and heteronuclear siliconoids to the substrate of our choice. Armed with a broad variety of preparative methods, we will then be able to exploit the unique electronic, magnetic and optoelectronic properties of benzpolarenes and other stable siliconoids by (a) their use as a new extremely electron-rich ligand class for homogeneous catalysis and (b) their application as functional motifs in materials. In subproject (a), we will focus on catalysis with earth-abundant base metals as we anticipate that the pronounced electron surplus of the siliconoids will lead to a non-innocent behavior as ligands that should be manifest in the support of two-electron redox steps otherwise not favored by 3d metals. The targeted species will be reminiscent of transition metals on silicon surfaces and thus serve as molecular model systems for heterogeneous catalysis. The influence of the unprecedented silicon-rich coordination environments on the performance will be used as a handle for the fine-tuning of these ligand systems. In subproject (b), a real bottom-up approach towards siliconoid materials will be developed. We will prepare nanostructured materials in one, two or three dimensions starting from functionalized siliconoids and suitable linking units and investigated them for cooperative effects brought about by the interlinkage and thus electronic communication of siliconoids. Overall, the project aims to close conceptual gaps between molecular silicon chemistry and that of the silicon bulk – with its applications in virtually all areas of modern society.

• DFG Programme: Research Grants
• International Connection: Austria, France
• Cooperation Partners: Privatdozent Dr. Raphael Johann Friedrich Berger; Professor Holger Vach, Ph.D.