Pentaatomic planar tetracoordinate silicon with 14 valence electrons: A large-scale global search of SiXnYmq (n + m = 4;q = 0, ±1, −2; X, Y = main group elements from H to Br)

Abstract

Designing and characterizing the compounds with exotic structures and bonding that seemingly contrast the traditional chemical rules are a never-ending goal. Although the silicon chemistry is dominated by the tetrahedral picture, many examples with the planar tetracoordinate-Si skeletons have been discovered, among which simple species usually contain the 17/18 valence electrons. In this work, we report hitherto the most extensive structural search for the pentaatomic ptSi with 14 valence electrons, that is, SiXnYm(q) (n + m = 4; q = 0, ±1, -2; X, Y = main group elements from H to Br). For 129 studied systems, 50 systems have the ptSi structure as the local minimum. Promisingly, nine systems, that is, Li3SiAs(2-), HSiY3 (Y = Al/Ga), Ca3SiAl(-), Mg4Si(2-), C2LiSi, Si3Y2 (Y = Li/Na/K), each have the global minimum ptSi. The former six systems represent the first prediction. Interestingly, in HSiY3 (Y = Al/Ga), the H-atom is only bonded to the ptSi-center via a localized 2c-2e σ bond. This sharply contradicts the known pentaatomic planar-centered systems, in which the ligands are actively involved in the ligand-ligand bonding besides being bonded to the planar center. Therefore, we proposed here that to generalize the 14e-ptSi, two strategies can be applied as (1) introducing the alkaline/alkaline-earth elements and (2) breaking the peripheral bonding. In light of the very limited global ptSi examples, the presently designed six systems with 14e are expected to enrich the exotic ptSi chemistry and welcome future laboratory confirmation.

Planar Tetracoordinate Silicon in Organic Molecules As Carbenoid‐Type Amphoteric Centers: A Computational Study

“…So far, we demonstrated the stability of ptSi molecules and showed that the π electron transfer from the peripheral ring to the central vacant Si 3p z orbital is the origin of the molecular stability. Here, we compared Si‐16–5555 with the experimentally validated ptSi compound, calix[4]pyrrole silicate, [7f] the structure of which is shown in the left of Figure 6 a (for the sake of simplicity its methyl group was replaced with a hydrogen atom). In this compound, we found a highly similar MO diagram and bonding pattern to the HOMO and LUMO+3 in Si‐16‐5555, that is, the Si 3p z is mainly involved in two MOs.…”

“…crystalized the structure of 1,3‐disila‐2‐oxyallyl‐borane adduct, which may be regarded as a rare case of ptSi molecules at room temperature [7e] . Furthermore, molecular clusters with 18 or 14 valence electrons SiAl 4 2− (18 e), SiIn 4 2− (18 e), SiC 2 Li 2 (14 e), HSiAl 3 (14 e), Ca 3 SiAl − (14 e), and Mg 4 Si 2− (14 e) were predicted to have a stable ptSi structure based on extensive theoretical calculations, [7f] and the tendency to form a planar tetracoordinate silicon is governed by the competition between the aromaticity and covalency in these clusters [9] . Significantly, the effect of a central planar tetracoordinate silicon was most recently confirmed experimentally in a methyl‐calix[4]pyrrole hydridosilicate, which is responsible for the remarkable stability of an anionic silicon hydride [7g] .…”

“…Since the work by Ebner et al. showing that the hybrid functional B3LYP‐D3 can well reproduce the experimental structure of calix pyrrole silicate, [7f] in this study, we chose the hybrid functional B3LYP‐D3 in the subsequent computations.…”

Linear, planar, and tubular molecular structures constructed by double planar tetracoordinate carbon D2h C2(BeH)4 species via hydrogen‐bridged BeH2Be bonds

“…Various ptC species or molecules have been realized experimentally or designed computationally. Furthermore, the concept of ptC bonding has also been extended to planar hypercoordinate carbon (phC) and planar bonding arrangements of heteroatoms and transition metals …”

“…Furthermore, the concept of ptC bonding has also been extended to planar hypercoordinate carbon (phC) [10][11][12][13][14][15][16] and planar bonding arrangements of heteroatoms and transition metals. [17][18][19][20][21][22][23][24][25][26] In addition to finding small species or molecules featuring phC(s), chemists have also explored whether the phC bonding could be applied to construct large molecular structures or bulky solids. Surveying previous studies, the reported large molecular structures/solids can be classified into three classes as summarized below.…”