Anionic Siliconoids from Zintl Phases: R3Si9− with Six and R2Si92− with Seven Unsubstituted Exposed Silicon Cluster Atoms (R=Si(tBu)2H). Issue 72 (11th December 2018) - Schiegerl, Lorenz J.
Abstract: Neutral and anionic silicon clusters (siliconoids) are regarded as important model systems for bulk silicon surfaces. For 25 years their formation from binary alkali metal silicide phases has been proposed, but experimentally never realized. Herein the silylation of a silicide, leading to the anionic siliconoids (Si( t Bu)2 H)3 Si9 − (1 a ) and (Si( t Bu)2 H)2 Si9 2− (2 a ) with the highest known number of ligand‐free silicon atoms is reported for the first time. The new anions are obtained in a one‐step reaction of K12 Si17 /NH3 (liq.) and Si( t Bu)2 HCl/THF. Electrospray ionization spectrometry and 1 H, 13 C, 29 Si, as well as 29 Si‐HMBC (heteronuclear multiple bond correlation) NMR spectroscopy, confirm the attachment of three silyl groups at a [Si9 ] 4− cluster under formation of1 a, in accordance with calculated NMR shifts. During crystal growth the siliconoid di‐anion2 a is formed. The single‐crystal X‐ray structure determination reveals that two silyl groups are connected to the deltahedral Si9 cluster core, revealing seven unsubstituted exposed silicon cluster atoms with a hemispheroidal coordination. The negative charges −1 and −2 are delocalized over the six and seven siliconoid Si atoms in1 a and2 a, respectively. Abstract : Closing the gap ! 25 years after Wiberg's synthesis of tetrahedro ‐tetrasilane from molecular precursors, the idea to use binary silicides was realized experimentally. The direct synthesis of soluble silicon‐rich molecules from solid K12 Si17 in a one‐step reaction allows now for an easy and direct access to molecules with a large number of ligand‐free Si atoms–so‐called siliconoids.