CSiGaAl2-/0 and CGeGaAl2-/0 having planar tetracoordinate carbon atoms in their global minimum energy structures

Density functional theory (DFT) is used to explore the structure, stability, and bonding in CSiGaAl2-/0 and CGeGaAl2-/0 systems having planar tetracoordinate carbon (ptC). The neutral systems have 17 valence electrons and the mono-anionic systems have 18 valence electrons. The ab initio molecular dynamics simulations for 2000 fs time at two different temperatures (300 and 500 K) supported the kinetic stability of the systems. From the natural bond orbital (NBO) analysis it is shown that there is a strong electron donation from the ligand atoms to the ptC atom. We have used Li+ ion for the neutralization of the mono-anionic systems and more interestingly it does not disrupt the planar structure. The most preferable site for binding of Li+ ion is along the Al-Al bond in both of the mono-anionic systems. All the systems in this work have both sigma and pi aromaticity which is predicted from the computations of nucleus independent chemical shift (NICS). Although the anionic species obey the 18 valence electronic rule, the neutral systems break the rule with 17 valence electrons. However, both sets of systems are stable in the planar form. The bonding analysis of the systems includes molecular orbital, adaptive natural density partitioning (AdNDP), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF) basin, and aromaticity analyses. The energy decomposition analysis (EDA) determines the interaction of Li+ ion with CSiGaAl2- and CGeGaAl2- in Li@SiGaAl2 and Li@GeGaAl2, respectively.

Automated summary

Density functional theory (DFT) is used to explore the structure, stability, and bonding in systems with planar tetracoordinate carbon. The study reveals the stable planar form in both neutral and mono-anionic systems, with strong electron donation from ligand atoms to the carbon atom.