Theoretical Study On Planar Hypercoordinate Carbon Superalkali Compounds

The design of new planar molecules is still a big challenge for chemists.In 1970,Hoffmann proposed the concept of"planar tetracoordinate carbon",which opened a new direction of carbon chemistry.Over half a century,under the unremitting efforts and exploring of scientific researchers,planar hypercoordinate carbon chemistry has been expanded from the traditional planar tetracoordinate carbon(pt C)to planar pentacoordinate carbon(pp C),and planar hexacoordinate carbon(p6C).Some effective strategies and valence electrons counting rules to design planar hypercoordinate carbon species have been proposed.In this thesis,using the quantum chemical method,some novel pt C and pp C superalkalis have been predicted,which further enrich planar hypercoordinate carbon chemistry.This thesis is divided into following five chapters:The first chapter introduces the development of planar hypercoordinate carbon chemistry,design strategy,the research content and significance of this thesis.The second chapter introduces the theoretical basis and calculation method of designing planar hypercoordinate carbon compounds.Chapter 3,theoretical study on planar tetracoordinate carbon clusters CLi Al₂E and CLi₂Al E(E=P,As,Sb,Bi)with 16 and 14 valence electron,respectively.In this section,starting from the pt C global minimum of C_2vCAl₃E(E=P,As,Sb,Bi),pt C CLi Al₂E and CLi₂Al E(E=P,As,Sb,Bi)have been designed by using the bonding similarity between Li atom and Al atom and the strategy of removing lone pair electron of ligands.The results show that CLi Al₂E and CLi₂Al E(E=P,As,Sb,Bi)species with 16 and 14 valence electrons(ve)have good thermodynamic and kinetic stability.Bonding analysis indicates that the stability of these pt C species are governed by the 2?+6?double aromaticity together with 8-electron shell structure of the pt C center.The results obtained in this work complete the series of 18ve,16ve,14ve and12ve CLi_nAl_3-nE(E=P,As,Sb,Bi;n=0-3)pt C series.In chapter 4,the prediction of planar pentacoordinate carbon superalkali cation C_2vCO₂Li₃⁺.In this chapter,we have predicted a intermediate structure between D_3hCO₃Li₃⁺and C_2v COLi₃⁺.D_3h CO₃Li₃⁺is the first global minimum with the p6C.Removing two O atoms in the structure of planar hexacoordination carbon D_3hCO₃Li₃⁺,the global minimum structure of pt C COLi₃⁺cation is formed.If only one O atom is removed from p6C CO₃Li₃⁺,we can get the pp C C_2vCO₂Li₃⁺cation.The results show that pp C CO₂Li₃ is the global minimum on the potential energy surface.The VEA value of CO₂Li₃⁺is 3.08 e V,which is lower than 3.89 e V of Cs atom and it can be considered as a superalkali cation.This work has complete the series of pt C,pp C,and p6C CO_nLi₃⁺(n=1-3)superalkali cations,which provides a new extension to the field of planar hypercoordinate carbon superalkali chemistry.In chapter 5,theoretical study on the planar tetracoordinate carbon CBe₄M₃⁺(M=Li,Na,K,Cu,Ag,Au)cation with 14 valence electron(ve).Using the metal cations Li,Na,K and Cu,Ag,Au to modify the basic structural unit CBe₄^2-,we predicted a series of stable planar tetracoordinate carbon(pt C)superalkali cations.We have conducted a systematic investigation on the structures and properties of CBe₄M₃⁺(M=Li,Na,K,Cu,Ag,Au)species.The results show that the global minima of CBe₄M₃⁺(M=Li,Na,K,Cu,Ag,Au)system are all pt C structures.Bonding analysis shows that the stability of these pt C species is governed by three five-center two-electron(5c-2e)?and one?bonds between the central C atom and Be₄ring,as well as three periphery Be-M-Be three-center two-electron(3c-2e)?bonds.It should be noted that,the CBe₄M₃⁺(M=Li,Na,K)cations have the lower VEA value than the Cs atom's IP(3.89e V),which can be considered as the superalkali cations.This work further expands the study of planar tetracoordinate carbon field.In chapter 6,summarizes the researchcontentandsignificance of this thesis and its significance in the field of planar hypercoordinate carbon compounds...