Theoretical Study On Bonding Characteristics And Stability Of Germylene Complex And Its Derivatives

Compared with the transition metals,the available price layer of the main element is less orbit,and it is occupied by the key electron pair or the non-forming bonding electron to varying degrees.This limitation prevents main group elements from having energy levels that can accommodate a variable number of unpaired electrons as the transition metals do,making it difficult to form stable complexes.However,with the improvement of experimental synthesis technology,more and more complexes of main group elements were discovered,and stable products were isolated.The main group elements show similar properties to transition metals,among which carbene were the most typical.Carbene,an important intermediate in many reactions,it has been separated and has been sufficiently studied,but relatively little is known about the heavier analogues of carbene.There are great differences in bonding characteristics between 14 groups of heavier elements（Si,Ge,Sn,etc.）and carbon.Therefore,the empirical rules of carbonization science are not completely applicable to these heavy elements.Based on the cooperation with experimental research,this article focuses on the bonding of germanium in germylene molecule.Through precise quantum chemistry calculation,combining with the chemical bond model and the wave function analysis method,the bonding features and stability of the newly synthesized low coordination germylene complex and derivatives were studied in detail,and the structure of such substances were deep understood.It provides theoretical basis for precise synthesis of novel molecules.This paper is mainly divided into four chapters.The first chapter is an introduction,including the characteristics of the main group element complexes,focusing on the research status of germylene complex and germylene derivative Ge₅R₄.The second chapter is the theoretical basis and analysis methods,mainly introduces Density Functional Theory（DFT）and wave function analysis methods,including bond level analysis,ELF analysis,AIM analysis,softness analysis,etc.In chapter 3,wave function analysis is used to analyze the bonding characteristics of low coordination germylene complexes.This chapter discussed the bonding characteristics and molecular skeleton stability of the separable lithium,iron and silicon-germanene complexes in detail,which were obtained by simple salt double decomposition reaction.This work optimized the compound through different functionals and basis sets,compared with the experimental crystal structure.Wave function analysis and chemical bond model were used to analyze the structure,and the interactions between lithium,iron,silicon and germanene were inferred to be ionic,polar and non-polar single bonds,respectively.The effect of side group on the structure and valence bond composition is also analyzed.The conjugation effect of electron donor group makes the delocalization degree of germanium bond orbital more obvious,and more electrons are concentrated in p orbital.In combination with HOMO orbital and NICS analysis,it was shown that the strong aromatization of the central C₃NGe ring enhanced the stability of the low-coordination germylene compound.In chapter 4,the interaction between several germanium atoms in germylene derivative Ge₅R₄（R=H,CH₃,Si Me₃）is analyzed based on the quantum chemical calculation method,and the stable isomer structure are predicted.There are only two types of stable Ge₅R₄ skeleton,pyramid structure and spiral ring structure,have been obtained in experiments,but the stability and synthesis feasibility of other isomers have not been proved by experimental and theoretical studies.Compared with the experimental results,we predict potential new isomers by analyzing the relative energy of free energy,bonding mode,bond strength and reaction ease by energy,ELF,AIM and softness analysis.And simply discuss the stability of the substitution group on the main skeleton with the increase of the side base.