Theoretical Investigation On The Planar Metal Tetracoordinate Carbon Stabilized By Oxygen/Sulfur-bridge

The concept of planar tetracoordinate carbon（pTC）was first proposed by Monkhorst et al.in 1968.The planar molecule with unique electronic properties and counter-traditional topology caught the interest of an amount of experimental and theoretical chemists,ever since the first pTC was designed by Hoffmann et al in 1970.However,the successful design of pTC is constrained by the strict electronic and stereoscopic effects between the central atoms and ligands,which lead to slow growth of pTC molecules.Investigation on pTC structure and stability help people better understand the bonding properties and rules,provide a theoretical reference for finding workable experimental preparation methods and design ideas for the construction of high-dimension material.Thus,in the present work,We explored the possibility of introducing O/S bridge bonds in the design of novel planar tetra-coordination carbon molecules by density functional theory.The research system includes palanr Transition metal tetracoordinate carbon stabilized by oxygen/sulfur-bridge and palanr aluminum tetracoordinate carbon stabilized by sulfur-bridge.The main research contents are summarized as follows:1.We first computationally designed a set of pTC species,i.e.,CM₄X₄ⁿ（M=Ni,Pd,Pt,Ag,Cu;X=O,S）.Although the pTC structure is not a global minimum structure of potential energy surface,it has good double aromatic stability.The atomization energy（AE）,molecular orbital and Nucleus-independent chemical shift NICS（1）of planar CNi₄O₄ are the most conducive to stability,comparing with CNi₄H₄ and CNi₄Cl₄ stability by hydrogen/chloride bridge.AdNDP orbitals show that planar CNi₄O₄ has double aromaticity and more delocalized partly orbital than CNi₄H₄ and CNi₄Cl₄.All of the above indicates that it is more reasonable to use oxygen bridge to stabilize transition metal tetracoordinate carbon,and it is concluded that the application of CNi₄O₄ with pTC may be better in the experiment.The Ni-O bridge was used to construct an aromatic BNi₄O₄^2-with planar tetracoordinate boron（pTB）,which has more excellent atomization energy,NICS（1）and AdNDP orbital than Ni-H bridge and Ni-Cl bridge.These all validate the potential advantages of the Ni-O bridge skeleton.2.At the B3LYP/def2-TZVP levels,We investigated S-bridge 18e CAl₄S^-with excellent thermodynamic and dynamic stability,so it has a high probability of being at the experiment.This result also verifies the validity of the 18 electronic counting rule on the carbon structure of the planar quadrangle.Based on S-bridge CAl₄S^-,we designed quasi-planar C_4v CAl₄S₄ⁿ（n=0,1,2）and the neutral CAl₄S_4,in which a carbon atom was higher than Al-plane 0.578?and sulphur atoms were lower than Al-plane 0.476?,gets the lowest energy in the three clusters.Meanwhile,CAl₄S₄ has most the stable structure of thermodynamics with double aromaticity,exploring the cause of its stability and providing a fresh idea for the extension of2D materials.