Molecular Silicon Clusters

Abstract

The continuously decreasing size of device features in microelectronics draws growing attention to the structuring of silicon at the molecular level with powerful tools provided by synthetic chemistry. Silicon clusters are of particular importance in this regard not only as potential precursors for silicon deposition but also as well-defined model systems for bulk and surfaces of silicon at the nanoscale as well as possible starting points for future construction of molecularly precise device structures. This review aims to give a comprehensive overview about the state of the art in the synthesis of molecular silicon clusters, which are grouped into (1) electron-precise saturated clusters, (2) soluble polyhedral Zintl anions, and (3) unsaturated silicon clusters, the so-called siliconoids. Particular attention is paid to functionalization as it is generally considered a necessary prerequisite for the design and construction of more extended systems. The interrelations between the three different classes of molecular silicon clusters, e.g., arising from the introduction of negatively charged functional groups, are highlighted on grounds of NMR properties and computed electronic structures.

A strongly twisted SiSi bond with resemblance to a buckled dimer in an unexpected isomer of hexasilabenzene

“…But the signal is significantly less deshielded than that of tetra-coordinate saturated silicon atoms ( δ 29 Si up to 187.3 ppm) in other siliconoids. 5,7…”

“…Silicon clusters, 5 that display unsubstituted silicon atoms, may also be considered as models for silicon surfaces. However, so far, their reactivity is limited and does not provide direct comparison with that observed for silicon(100)2 × 1 surfaces.…”

“…2), 6 and the term siliconoid was defined for it. 5,7 The unsubstituted vertices in these clusters display an inverted tetrahedral geometry 8 or hemispheroidal configuration, 7 because all bonds of these atoms point to one hemisphere. This is the case in the propellane-type clusters B 9 and C 10 and in the hexasilabenzene isomer D (Fig.…”

Cluster Chemistry with ( Pseudo -)Tetrahedra Involving Group 13–15 (Semi-)Metal Atoms

“…58 For synthetic reasons and owing to better kinetic stabilization, most of the other reported heavier group 13 and 14 congeners exhibit shielding by silyl substituents, such as found in ( t Bu3SiTr)4 (Tr = Al, Ga), ( t Bu3SiTt)4 (Tt = Si, Ge) and (LTr)4 (L = (Me3Si)3C; Tr = In, Tl). [13][14][15][16][17][18][19][20][21]59 However, there are a few special cases: anionic [{(SiMe [{(SiMe3)3C}6Ga8] was obtained under similar conditions, by reaction of GaBr with LiC(SiMe 3 ) 3 at −78°C. However, the molecular structure of the latter shows obvious differences compared to the {Al 7 } motifs, with two tetrahedral {Ga 4 } units being linked through a Ga−Ga bond.…”

Utilization of 29Si MAS-NMR to Understand Solid State Diffusion in Energy Storage Materials

“…For an LIB silicon electrode, a fully charged anode mainly contains the Zintl phase Li 15 Si 4 . Using Zintl-Klemm rules, the stoichiometry and properties of this phase can be understood as being composed of a combination of fully reduced four Si −4 anions, surrounded by 15 lithium cations per unit cell (Heider and Scheschkewitz, 2021). Using these rules, the phase is formally electron rich (exact charge balance would be 16 lithium cations) and is metastable at room temperature at this defect stoichiometry.…”