In Silico Studies on Selected Neutral Molecules, CGa2Ge2, CAlGaGe2, and CSiGa2Ge Containing Planar Tetracoordinate Carbon

Prasenjit Das,Pratim Kumar Chattaraj

doi:10.3390/atoms9030065

Abstract

Density functional theory (DFT) was used to study the structure, stability, and bonding in some selected neutral pentaatomic systems, viz., CGa2Ge2, CAlGaGe2, and CSiGa2Ge containing planar tetracoordinate carbon. The systems are kinetically stable, as predicted from the ab initio molecular dynamics simulations. The natural bond orbital (NBO) analysis showed that strong electron donation occurs to the central planar carbon atom by the peripheral atoms in all the studied systems. From the nucleus independent chemical shift (NICS) analysis, it is shown that the systems possess both σ- and π- aromaticity. The presence of 18 valence electrons in these systems, in their neutral form, appears to be important for their stability with planar geometries rather than tetrahedral structures. The nature of bonding is understood through the adaptive natural density partitioning analysis (AdNDP), quantum theory of atoms in molecules (QTAIM) analysis, and also via Wiberg bond index (WBI) and electron localization function (ELF).

Highlights

Nowadays, planar tetracoordinate carbon molecules showed great attention to experimentalists [1,2,3,4,5,6,7] as well as theoreticians [8,9,10,11,12,13,14,15] because it deviates from the usual ideas of tetrahedral tetracoordinate carbon
The L and planar tetracoordinate carbon (ptC) systems were optimized without any symmetry constraint
We considered only the singlet state of the ptC systems because the higher spin states correspond to a higher energy than the singlet state

Summary

Introduction

Planar tetracoordinate carbon (ptC) molecules showed great attention to experimentalists [1,2,3,4,5,6,7] as well as theoreticians [8,9,10,11,12,13,14,15] because it deviates from the usual ideas of tetrahedral tetracoordinate carbon. Some new anionic ptC molecules, CAl42−, CAl3Ge−, CAl3Si−, and NaCAl4−, were experimentally detected [7,31,32] This idea of ptC has been extended to design planar pentacoordinate [33,34,35] and hexacoordinate carbon molecules [36,37,38,39]. Boldyrev and Simons [2] studied on three neutral pentaatomic molecules (CSi2Al2, CSi2Ga2, and CGe2Al2) and showed the planar tetracoordinate central carbon (ptC) in these systems They used molecular orbital analysis to rationalize the preference of the planar geometry over the tetrahedral one and they concluded that molecules containing one central C and two Si or Ge ligand atoms and two Al or Ga ligand atoms should have stable planar geometries. The nature of bonding includes molecular orbital analysis, AdNDP analysis, NBO analysis, and electron density analysis

Computational Details

Geometries

Aromaticity Analysis

Summary and Conclusions