Stability Studies Of N₄^4-,N₆^n- Anions And Their Nitrogen-Rich Compounds

All-nitrogen compound is a new type of high energy density material,which will play an important role in rocket propellants,pyrotechnics,explosives and other fields if successfully developed,so its research is one of the hot spots of contemporary research.Qualified high-energy density materials usually meet two requirements:high exothermicity and high stability.Firstly,high exotherm means that the compound can release a large amount of heat when decomposing,and all-nitrogen compounds generally meet this condition.Secondly,high stability means that the compound has good kinetic stability.But compounds that can release large amounts of heat are usually unstable when kinetic,and this is also true for all-nitrogen compounds.It is one of the challenges for chemists to improve the kinetic stability of all-nitrogen compounds while maintaining high exothermicity.So far,several pure nitrogen compounds containing odd number of nitrogen atoms have been synthesized experimentally,while all-nitrogen compounds containing even number of nitrogen atoms have not been synthesized yet.In this thesis we predicted two all-nitrogen molecules containing even number of nitrogen atoms,N₄^4-and N₆^n-anions,and investigated their stability.Based on this,we introduced heteroatoms bonded to N₄^4-and N₆^n-and predicted a series of nitrogen-rich compounds and investigated their stability in order to find ways to effectively improve the stability of all-nitrogen compounds containing even number of nitrogen atoms.In this paper,two N₄^4-anions with planar tripod and zigzag structures,respectively,were predicted by CALYPSO software.And the structures and stability of the two N₄^4-anions were investigated by density functional theory.In addition,we introduced H⁺bonded with N₄^4-anions to form neutral N₄H₄molecules and predicted to obtain a series of N₄H₄molecules.The structures and stability of N₄H₄were also investigated,and it was found that N₄H₄isomers have higher kinetic stability than the N₄^4-anions.Finally,the half-life of the decomposition reaction of N₄H₄was calculated and it was found that the N₄H₄molecule can be stable exist stably at ambient conditions.The stability of the N₄^4-structures were greatly improved by the introduction of H⁺.In addition,a series of N₆^n-（n=1,2,6）anions were predicted by CALYPSO software and a systematic theoretical study of them was carried out.It is found that the N₆^n-anions have good kinetic stability when n=2.And among them,the N_6b^2-anions containing a five-membered ring structure have excellent kinetic stability.In addition,the stability of a series of nitrogen-rich compounds MN_6x（x=a and b,M=Be,Mg,Ca）consisting of N₆^2-anions with main group 2 group elements have been explored.Among them,the introduction of Ca²⁺improves the stability of the N_6b^2-anion to some extent.