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

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.

Silylated Ge9 Clusters as New Ligands for Cyclic (Alkyl)amino and Mesoionic Carbene Copper Complexes.

The coordination of Ge9 Zintl clusters at (carbene)CuI moieties is explored, and the complexes [(CAAC)Cu]2[η3-Ge9{Si(TMS)3}2] (1), (CAAC)Cu[η3-Ge9{Si(TMS)3}3] (2), and (MIC)Cu[η3-Ge9{Si(TMS)3}3] (3) are compared with their known N-heterocyclic carbene (NHC) derivatives (A and B), where CAAC = cyclic (alkyl)amino carbene, MIC = mesoionic carbene, and TMS = trimethylsilane. In analogy to the NHC derivatives, the synthesis of 1-3 proceeds by single-step reactions of (CAAC)CuCl or (MIC)CuCl with the [Ge9R2]2- and [Ge9R3]- [R = Si(TMS)3] cluster ligands, respectively, and yields complexes of (carbene)CuI (carbene = CAAC, MIC) moieties exhibiting η3-coordination modes of the Ge9 deltahedron to the Cu atom. In 1, [Ge9R2]2- acts as a η3-bridging unit for two (CAAC)CuI moieties, and 2 and 3 feature single (carbene)CuI (CAAC and MIC) fragments η3-connected to [Ge9R3]- units. Analysis of the bond lengths in comparison with known examples shows a bond expansion within the coordinated Ge3 triangular faces for all (carbene)CuIGe9 complexes (carbene = NHC, MIC, CAAC). All compounds are characterized by single-crystal X-ray diffractometry, NMR spectroscopy [1H, 13C{1H}, and 29Si{1H}], electrospray ionization mass spectometry, elemental analysis (C, H, and N), and for the first time also by IR and Raman investigations (for 2 and 3). The new complexes add to the known NHC derivatives and extend the exploration of Ge9 clusters with carbene ligands at CuI atoms.

Anionic Siliconoids from Zintl Phases: R3 Si9 - with Six and R2 Si9 2- with Seven Unsubstituted Exposed Silicon Cluster Atoms (R=Si(tBu)2 H).

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(tBu)2 H)3 Si9 - (1 a) and (Si(tBu)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(tBu)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 of 1 a, in accordance with calculated NMR shifts. During crystal growth the siliconoid di-anion 2 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 in 1 a and 2 a, respectively.

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.

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.

On the Reactivity of Silylated Ge9 Clusters: Synthesis and Characterization of [ZnCp*(Ge9 {Si(SiMe3 )3 }3 )], [CuPiPr3 (Ge9 {Si(SiMe3 )3 }3 )], and [(CuPiPr3 )4 {Ge9 (SiPh3 )2 }2 ].

We report on the synthesis of new derivatives of silylated clusters of the type [Ge9 (SiR3 )3 ]- (R = SiMe3 , Me = CH3 ; R = Ph, Ph = C6 H5 ) as well as on their reactivity towards copper and zinc compounds. The silylated cluster compounds were synthesized by heterogeneous reactions starting from the Zintl phase K4 Ge9 . Reaction of K[Ge9 {Si(SiMe3 )3 }3 ] with ZnCl2 leads to the already known dimeric compound [Zn(Ge9 {Si(SiMe3 )3 }3 )2 ] (1), whereas upon the reaction with [ZnCp*2 ] the coordination of [ZnCp*]+ to the cluster takes place (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) under the formation of [ZnCp*(Ge9 {Si(SiMe3 )3 }3 )] (2). A similar reaction leads to [CuPiPr3 (Ge9 {Si(SiMe3 )3 }3 )] (3) from [CuPiPr3 Cl] (iPr=isopropyl). Further we investigated the novel silylated cluster units [Ge9 (SiPh3 )3 ]- (4) and [Ge9 (SiPh3 )2 ]- (5), which could be identified by mass spectroscopy. Bis- and tris-silylated species can be synthesized by the respective stoichiometric reactions, and the products were characterized by ESI-MS and NMR experiments. These clusters show rather different reactivity. The reaction of the tris-silylated anion 4 with [CuPiPr3 Cl] leads to [(CuPiPr3 )3 Ge9 (SiPh3 )2 ]+ as shown from NMR experiments and to [(CuPiPr3 )4 {Ge9 (SiPh3 )2 }2 ] (6), which was characterized by single-crystal X-ray diffraction. Compound 6 shows a new type of coordination of the Cu atoms to the silylated Zintl clusters.