Silicon's Building Block Synthesized

Inorganic Chemistry

The smallest discretely defined repeat unit that can be plucked from the silicon crystal lattice has been synthesized as an independent molecule by a team of Austrian chemists (Science 2005, 310, 825).

Sila-adamantane, as the new compound is called, is a tricyclic Si₁₀ cluster with pendant methyl and trimethylsilyl groups. The molecule is anticipated to help scientists better understand how the properties of silicon transition from the molecular level to the bulk solid.

Sila-adamantane was synthesized by Jelena Fischer, Judith Baumgartner, and Christoph Marschner of Graz University of Technology. The compound has the same structure as adamantane, the carbon compound that serves as the repeat unit in diamond, one of carbons structural allotropes.

Marschners group had previously synthesized a bicycloheptasilane compound. To make sila-adamantane, the researchers derivatized the heptasilane by attaching a cyclohexylsilanyl group. This substituted bicyclic precursor was then treated with AlCl₃, which catalyzed its rearrangement to the adamantane tricyclic structure.

Lewis-acid-catalyzed rearrangement of silanes is well-known. In the case of sila-adamantane, the reaction involves converting dimethylsilylene moieties in the precursors rings to trimethylsilyl and quaternary silicon centers.

Adamantanes containing several silicon atoms have been prepared before. Sila-adamantane also is related to silsesquioxanes, a family of cluster compounds made up of a network of silicon and oxygen atoms. These inorganic-organic hybrids are potential materials for ceramics and electronics.

Marschner tells C&EN that sila-adamantanes structure should impart properties that could make it suitable for use in molecular electronics, such as constructing molecular wires and miniaturized semiconductor devices.