Charged Si9 Clusters in Neat Solids and the Detection of [H2 Si9 ]2- in Solution: A Combined NMR, Raman, Mass Spectrometric, and Quantum Chemical Investigation.

Abstract

Polyanionic silicon clusters are provided by the Zintl phases K4 Si4 , comprising [Si4 ]4- units, and K12 Si17 , consisting of [Si4 ]4- and [Si9 ]4- clusters. A combination of solid-state MAS-NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum-chemical investigations was used to investigate four- and nine-atomic silicon Zintl clusters in neat solids and solution. The results were compared to 29 Si isotope-enriched samples. 29 Si-MAS NMR and Raman shifts of the phase-pure solids K4 Si4 and K12 Si17 were interpreted by quantum-chemical calculations. Extraction of [Si9 ]4- clusters from K12 Si17 with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si9 clusters. This compound was characterized by elemental and EDX analyses and 29 Si-MAS NMR and Raman spectroscopy. Charged Si9 clusters were detected by 29 Si NMR in solution. 29 Si and 1 H NMR spectra reveal the presence of the [H2 Si9 ]2- cluster anion in solution.