Theoretical Study On The Bonding Properties Of Xe

Chemical bond is the core of basic chemistry.It exists in a region between the equipotential surface of two nuclei,where the total energy of the system is the lowest and the interaction between two atoms is the strongest.Traditional chemical bonds include ionic bonds,covalent bonds,metal bonds and so on.With the deepening of theoretical research,many new types of chemical bonds are emerging continuously,such as sulfur-containing multiple bonds(S≡CBO,S≡BeCO),transition metal-containing multiple bonds(Mo-Mo six-fold bonds),multi-center bonds(the 3c-2e bond in H3+,the 3c-2e bond in B2H6)and the bonding of noble gas elements(Xe-AuF,HXe-XeF,F4Xe≡OsF4)and so on.Therefore,further expansion of the basic research of chemical bonds is conducive to understanding the knowledge of chemical bonds.Noble gas(Ng)compounds have always been one of the hotspots in the study of noble gas chemistry.Xe is easy to interact with other elements due to its full 4d orbital electrons and the characteristics of its outermost electron being far from the nucleus and weak bound by the nucleus.Therefore,the types and quantities of noble gas compounds containing Xe bonds are the most extensively studied.In this paper,a series of noble gas compounds containing Xe bonds have been studied by using density functional theory.The following research results have been obtained by exploring the equilibrium geometric structure,molecular orbital bonding,electronic localization functions and related topological properties:The Xe-Mo bond in the molecule of X2XeMoY2(X=F,Cl,Br;Y=F,Cl,Br)belongs to a covalent double bond,and the calculated bond lengths are 2.516～2.604 (?).Taking the F2XeMoCl2 molecule as an example,the bonding orbitals of the Xe-Mo bond are 1σ and 1π,respectively,and the 1σ orbital is mainly composed of 85.17%Xe(s0.34p)and 14.83%Mo(s0.10p0.04d);1π orbital is mainly composed of 13.86%Xe(p)and 86.14%Mo(p0.01d).Through comparative analysis,it is concluded that the greater the electronegativity of the halogen atom connected to the Xe atom,the lower the electronegativity of the halogen atom connected to the Mo atom,and the shorter the length of the Xe-Mo double bond.On the basis of molecules containing Xe double bonds,we continue to explore the system containing Xe triple bonds and found that Xe-N can form covalent triple bonds in the NXeH4+ion.The Xe-N bond length value is 1.813 (?) calculated by MP2 level of method,which is slightly larger than its standard covalent triple bond radius bond length of 1.76 (?),and smaller than its standard covalent double bond radius bond length value 1.95 (?).Molecular orbital analysis and basin analysis based on electron localization function analysis show that the Xe-N bond is a covalent triple bond.The higher energy barrier on the reaction path indicates that the NXeH4+ion is kinetic stability.Considering the strong bonding ability of Xe,the bonding system containing Xe in the material has been further explored.It is found that Xe can combine with the N in the hexamethylenetetraamine(HMT)to form a cage molecule C5N4H10XeH2 containing Xe-N bonds.Expanding the cage molecule can give a polymer structure containing Xe-N bonds CH2Y(XeY)nCH2(Y=C4N4H8),and two-dimensional structure with Xe-N bond as grid skeleton.Topological analysis shows that the Xe-N bonds in this system are all partially covalent bonds.By introducing Xe into polyhedral sesquiloxane(POSS)material(HSiO3/2)n(n=6,8),it is found that the hollow POSS cage structure can be used as a carrier for storing Xe,and the inclusion complex structure Xe@POSS is obtained.Xe destroys the POSS cage structure during the process of leaving the POSS cage,and becomes a part of the cage framework to form a new cage compound containing Xe-O bonds and Xe-Si bonds.Exploring the storage of lighter Ng atoms in the POSS cage,it was found that Ng in Ng@POSS(Ng=He,Ne,Ar)can pass through a certain reaction energy barrier,and finally leave the POSS cage completely without damaging the cage molecules.Therefore,POSS cage molecules have a better storage effect on lighter noble gases(He,Ne or Ar),especially for the storage of He atoms.The energy barrier for He desorption in He@(HSiO3/2)6 is 21.8 kcal mol-1.