Theoretical Study On The Structures And Bonding Properties In The Inserted Noble Gas Organic Compounds

The preparation of Xe⁺[PtF₆]^-unveiled the prelude to the study of noble gas chemistry,and then ever-increasing noble gas compounds were synthesized experimentally or investigated theoretically.At present,insertional noble gas compounds are the focus of noble gas chemistry research,whereas the experimental and theoretical investigations of noble gas compounds are mainly focused on the HNg Y-type compounds.Consequently,in this paper we theoretically investigated the geometric configuration,stability and bonding properties of the inserted noble gas organic compounds.The specific details of the study are as follows.（1）The equilibrium structures and transition states of metal-or halogen-substituted pyridine as the parent of inserted Ng compounds MNg C₅H₄N and XNg C₅H₄N were subjected to structural optimization and frequency calculations using DFT and MP2 methods combined with the def2-TZVPPD basis sets.It’s found that MNg C₅H₄N and XNg C₅H₄N are planar molecules with a linear M-Ng-C and X-Ng-C structure.The effects of metals M（Li/Na,Cu/Ag/Au）and halogens X（F/Cl/Br）on the bonding properties of inserted organic noble gas compounds were investigated using the NBO,NRT,AIM and ELF methods.There is considerable bond order（WBI values）between M/X and C in MNg C₅H₄N and XNg C₅H₄N,ranging from 0.1 to 0.5,indicating the presence of long bond interactions across Ng in the M-Ng-C and X-Ng-C moieties.AIM and ELF analyses indicate that the M-Ng and Ng-C bonds are typical ionic bonds in Li/Na compounds,while they are partially covalent or covalent bonds in transition metal Cu/Ag/Au compounds,and F-Ng bonds and all Ng-C bonds in halides are typical covalent bonds.The dissociation of MNg C₅H₄N and XNg C₅H₄N molecules releasing Ng is an exergonic and exothermic spontaneous process with with a high reaction energy barrier,while all other channels are exergonic and exothermic non-spontaneous,indicating that the compounds MNg C₅H₄N and XNg C₅H₄N are thermodynamically sub-stable and kinetically stable.The C atoms in the pyridine ring participates in bonding with sp²hybridisation,forming a chemical bond with bond lengths and strengths lying between sp-C and sp³-C.The N lone pair of electrons enhances the stability of the C-Ng bond in the C-Ng-M/X group by hyperconjugation to the twoπ*（C-C）orbitals between the other C atoms in the pyridine ring.（2）The structures of metal-substituted compounds MNg R with ethane,ethylene and acetylene as the parent were optimized using the MPW1B95,B3LYP-D3,MP2,and DSD-PLYP-D3 methods.Seven dissociation pathways were considered in the reseach to demonstrate their substable nature.NBO/NRT analysis shows that the M-Ng-C moiety with a long 3c-4e bond can be described by three main resonance structures,including two localw-bond structures and oneσ-bond structure.The C atom attached to Ng in MNg R is involved in bonding with a spⁿhybridization orbital(sp,sp^2.8-6.4and sp^10.2-47.5),respectively,and the p component of the hybridization orbitals gradually increases.The bond lengths of M-Ng and Ng-C increase in the order of CCH,C₂H₃and C₂H₅as the p-orbitals of the hybridized orbitals gradually increase in composition,while their strengths weaken in this order.AIM and ELF analyses show that the M-Ng and Ng-C bonds are of partial covalent character.The bonding properties of Au are different from those of Cu and Ag.Au has a large relativistic effect leading to contraction of 6s orbitals and expansion of 5d orbitals to participate in bonding with 6s-5d hybrid orbitals thus forming shorter and stronger bonds.This study will help to understand the bonding properties of noble gas in metal-organic compounds and further expand the application of noble gas chemistry in organic chemistry.（3）The equilibrium structures and transition state geometries were optimized for linear inserted noble gas compounds FNg C_nN and planar noble gas compounds FNg C₅H₄N,FNg C₃H₂N₃,FNg CN₅using the MPW1B95,M06-2X-D3 and MP2 methods in combination with the def2-TZVPPD basis set,and vibrational analyses were performed.The bonding properties of the linear and planar noble gas compounds were investigated using the NBO,AIM and ELF methods.The results show that FNg C_nN is a linear molecule,while FNg C₅H₄N,FNg C₃H₂N₃and FNg CN₅are planar molecule.The sub-stable nature of the molecule was demonstrated thermodynamically and kinetically by considering possible dissociation pathways,finding transition states for the reaction and calculating reaction energy barriers.NBO analysis reveals the existence of bond order（WBI values）between F and C atoms in the FNg R molecule and greater than 0,indicating some overlap between the orbitals of the F and C atoms,forming specific interactions across the Ng atoms.Electron density topology analysis shows thatρ（r_c）>0.1 a.u.and▽²ρ（r_c）<0 or H（r_c）<0 and G（r_c）/ρ（r_c）<1 at the at the bond critical point of F-Ng bonds and Ng-C bonds in FNg R molecules,indicating that F-Ng bonds and Ng-C bonds are typical covalent bonds.In addition,the growth of the organic carbon chain contributes to the stability of the FNg Cn N molecule.The stronger the electronegativity of the group R,the stronger the F-Ng bond in the FNg R molecule and the shorter the bond length.