Silicon clusters with six and seven unsubstituted vertices via a two-step reaction from elemental silicon.

Lorenz J Schiegerl,Wilhelm Klein,Antti J Karttunen,Thomas F Fässler

doi:10.1039/c9sc03324f

Abstract

Unsaturated silicon clusters with only partial substitution, and thus, "naked" Si atoms are well studied species as they are proposed intermediates in gas-phase deposition processes. Although a remarkable number of stable molecular clusters has been reported, they are typically still obtained by multi-step syntheses. Herein we introduce a newly developed synthetic approach which led to the formation of the anionic species {Si(TMS)3}3Si9 - (1a) and {Si(TMS)3}2Si9 2- (1b), and an extension of this synthetic protocol resulted in the first covalent attachment of ligands through metal atoms to these clusters, (SnCy3)3Si9 - (2a) and (SnCy3)2Si9 2- (2b). The influence of the substituents on the electron localization in the central Si9 unit is analyzed by means of intrinsic bond orbital (IBO) analysis and partial atomic charge distribution. The IBO analyses reveal a new type of delocalization including 5-center-6-electron besides 3-center-2-electron bonds. The Raman spectra of 1b and 2b allow an assignment of the Si-Si intra-cluster vibrations by comparison to calculated (DFT-PBE0) spectra. The anions are formed in a one-step synthesis from binary K12Si17 which can easily be obtained by fusing the elements K and Si. The anions are characterized by ESI mass spectrometry and comprehensive NMR studies (1H, 13C, 29Si, 119Sn). Attempts to crystallize 1a and 2a as their (K-222crypt)+ salts yielded after the loss of one of the substituents single crystals containing 1b and 2b. The single crystal X-ray structure analyses reveal the presence of anionic siliconoids with surfaces of seven unsubstituted silicon atoms.

Highlights

The call for new sources of silicon-based materials is steadily increasing due to applications in numerous daily-life products as e.g. batteries, photovoltaics and electronic devices.[1,2,3,4,5,6,7,8] The wide range of applications is promoted by the abundancy, low costs, non-toxicity and semiconducting properties of silicon
In 1993, Wiberg et al already suggested in their report on the synthesis of (SitBu3)4Si4 that such substituted Si4 cluster compounds should probably be accessible in a more straightforward manner through the reaction of alkyl halides with tetrahedral Si44À polyanions that occur in binary alkali metal alloys of silicon.[32]
Reactions of Ge9 clusters from the K4Ge9 precursor with such reactants led to an attachment of silyl[51,57,58,59,60,61] and stannyl[62,63] groups at the cluster cores, and the products were characterized as tri-substituted cluster species by Electronic supplementary information (ESI)-MS and NMR investigations in solution as well as by X-ray analysis in solid-state

Summary

Introduction

The call for new sources of silicon-based materials is steadily increasing due to applications in numerous daily-life products as e.g. batteries, photovoltaics and electronic devices.[1,2,3,4,5,6,7,8] The wide range of applications is promoted by the abundancy, low costs, non-toxicity and semiconducting properties of silicon. We used Si9 clusters from the precursor K12Si17 for the production of the anionic siliconoids (SiHtBu2)3Si9À (3a) and (SiHtBu2)2Si92À (3b, Fig. 1d) via direct ligand attachment.[30] The silylation of Si9 clusters by the reaction of K12Si17 with SiHtBu2Cl yields species with covalently bonded SiHtBu2 groups at the cluster vertex atoms.

Results

Conclusion