Theoretical Study On The Construction And Characteristics Of Ns² Np⁰-type Homonuclear Diatomic?be₂,zn₂?chemical Bond

As one of the basic research fields of chemistry,chemical bond is the binder that constitutes the chemical world and the cornerstone of the chemical edifice.Among the various types of chemical bonds,the exploration of metal-metal?M-M?bonds has been one of the most popular and important themes in the field of chemical bond researches,because it is a fertile territory to further understand the nature of electronic structure,orbital bonding,reactivity,reaction mechanisms and properties of corresponding compounds due to the occupation of complex and changeable electrons and the orbital hybrid forms of metals,especially for transition metals.It continues to challenge our understanding of the nature of chemical bonds.The apparent chemical bond order is zero in the ns²np⁰-type?Groups 2 and 12?homonuclear diatomic molecules based on the simple molecular orbital theory,although there is a weak interaction between two atoms due to electron correlation effects.Hence there is no genuine chemical bond between two atoms.At present,the researches on such molecules have mainly focused on how to shorten the distance and/or how to strengthen the chemical bond strength.For the latter,the general strategy is to introduce electron-withdrawing groups such as F,CN^-at both ends of the M-M axis to take away the electrons lying on the ? anti-bonding orbital of M₂ and to form a M-M single bond???,or strong electron-donating ?-acid ligands such as CO,N-heterocyclic carbenes?NHCs?to delocalize electrons to the empty bonding orbitals of M₂ to construct M=M double bond?? + ??.In this way,a chemical bond is formed by taking away?supplying?even number?two?electrons from?to?M₂ simultaneously.In this thesis,we use theoretical calculation methods to discuss the electronic structure and reveal the nature of internal chemical bonds of Be-Be/Zn-Zn?mainly discuss Be-Be?bonding structures constructed by the strategy of donating?removing?electrons one-by-one.The main research contents of this thesis are as follows:1.In terms of the difficulty to construct the second ? bond between M-M?M=Be,Zn?,we innovatively introduce four s¹-type electron-donating ligands?L = Li,Na,K,Cu,-BeF,-BeCl,etc.?from the equatorial plane of M-M and firstly achieve a degenerated double ? bond without ? bond between M-M?second ? bond?.Although ?-acid ligands such as CO,N-heterocyclic carbenes?NHCs?can be used to build multiple bonds between M-M successfully,they destroys the original orbital symmetry of M₂,hence only the classic double bond??+??is formed.2.Since an s¹-type electron-donating ligands only donate one electron to M-M fragment,the bond order of M-M can be adjusted by the number of s¹-type ligands.On the basis of the degenerated Be=Be double ? bonding system D_4h-Be₂X₄?X= Li,Na?,two s¹-type electron-donating ligands are further introduced from both ends of Be-Be along the Be-Be axis and the Be?Be triple bond can be constructed.Remarkably,we first identified a perfect classical Be?Be triple bond in D_4h-Be₂Na₄K₂.By virtue of the electrostatic potential mapping of the D_4h-Be₂X₄ clusters,the Be₂X₄Y₂?Y = Li,Na,K?trans-bent geometries and the Be?Be triple bonds inside were both well interpreted.This concerted electron-donating strategy proves that it is feasible for elements of s and ds blocks to strengthen their chemical bonds through the p orbital overlapping by using of the s¹-type ligands,and the central metals of Be and Zn possess a negative oxidation state simultaneously.3.Using s¹-type electron-donating ligands to supply electrons to the empty bonding orbitals of Be₂ can construct a Be-Be bond,similarly,transferring electrons from the Be₂ fragment one by one can also adjust the Be-Be bond order.We use amidinate ligands to chelate two Be atoms simultaneously in a side-on coordination?the structures are proved to be their global minimum energy structures?and gradually reduce the electrons of the Be₂ fragment by increasing the number of amidinate ligands.The odd-electrons Be-Be bonds are confirmed under neutral conditions for the first time.In addition,the hybrid form of the central Be atom also changes synchronously with the number of amidinate ligands.