Theoretical Study On The Structure And Bonding Properties Of Rare Gas Inorganic Compounds

Rare gas(Rg)are often called“inert gas" with saturated valence electron states.The successful discovery of rare gas compounds has removed the title of "inert" for rare gases,making them particularly interesting in the periodic table of elements.So far,large numbers of rare gas compounds have been found theoretically or experimentally.Theoretical methods can be effectively used to determine the geometric structures and predict the physical and chemical properties of the rare gas compounds.In this paper,we predict some new rare gas inorganic compounds theoretically,and study their molecular structures,stability and bonding properties systematically.The main contents are as follows.A series of donor-acceptor type of rare gas compounds BnRgn(n-2)+(n=3-6,Rg=He-Rn)was predicted by use of the density functional theory(DFT),MP2 and CCSD(T)methods combined with def2-nZVPPD(n=T and Q)basis sets.The bonding nature of Rg was analyzed by AIM,NBO and EDA.By means of a great deal of calculations,one more structure for B4Rg42+,12 extra isomers for B5Rg53+ and 39 extra isomers for B6Rg64+besides the above desired monocyclic configurations are found.The global minima of B4Ar42+and B5Ar53+are monocyclic structures with Dnh symmetries compared with their isomers.However,the global energy minimum of B6Rg64+is a regular octahedral cage.The monocyclic B6Rg64+is metastable,and its energy is about 23 kcal mol-1 higher than octahedral structure.In these monocyclic BRg cations(Rg=Ar-Rn),the Rg-B bond length is close to the sum of the covalent radii of Rg and B.The bond energy is quite high in the range of 15-95 kcal mol-1.The bond order of Rg-B is larger than 1/2 and close to 1.The Rg-B bonds for Ar-Rn are typical covalent bonds.The Rg-B bond is mainly stabilized by the ?-donation from the valence p orbital of Rg to the LUMO of the boron ring.The stability of Be3B3+and Rg-Be3B3+compounds were reported.The isomers of Be3B3+were studied at the B3LYP/LanL2DZ and B3LYP/def2-TZVP levels.It is confirmed that the D3h symmetric Be3B3+ is the global minimum on the potential energy surface.Ten relatively stable isomers of Be3B3+ and RgBe3B3+ were compared for their stability and bond energy.After that,RgnBe3B3+ compounds formed by the most stable Be3B3+ and Rg were studied systematically.The Rg-Be bond lengths of RgnBe3B3+(n=1,2(m),3(m))are very close to the sum of covalent radii of Rg and Be.For a given Rg,RgBe3B3+has the largest binding energy in the range of 2-26 kcal mol-1 from He to Rn.The Wiberg bond order of He/Ne-Be bond in the RgnBe3B3+is 0.1-0.2,indicating that He/Ne-Be is a noncovalent interaction.In the same series of RgnBe3B3+,the Wiberg bond order increases from Ar(0.34)to Rn(0.68).The topological analysis of electron density shows that the electron density at the bond critical point of Rg-Be bond increases gradually.For the Kr/Xe/Rn Be bond,there is an accumulation of electron density between Rg(Kr-Rn)and Be,which means the covalent nature of the Rg-Be bond.EDA reveals that the stability of Rg-Be bond is due to the orbital interaction of the Rg and Rgn-1Be3B3+ fragments,that the ?Eorb plays a significant role in the total attraction energy.The Rg?Rgn-1Be3B3+?-donation is the major contribution towards ?Eorb for all these compounds.Besides,other two Rg?Rgn-1Be3B3+?-donations also play important roles in stabilizing the Rg-Be bonds.The structural optimization and frequency calculation were carried out for the stable and transition states of FRgBMF2(Rg=Ar-Rn,M=Ti,Zr and Hf).The F-Rg bond lengths of FRgBTiF2 are 2.084 A,2.131 A,2.196 A and 2.256 A from Ar to Rn,respectively.The F-Rg bonds of FRgBZrF2 and FRgBHfF2 are slightly longer than those of FRgBTiF2.The bond length of Rg-B is in the range of covalent single bond.Four possible dissociation processes of FRgBMF2 are considered.The bond order of F-Rg is less than 0.2,while that of Rg-B is greater than 0.5.ELF shows that there is almost no electron localized region between F and Rg,indicating that F-Rg should be an ion bond.However,there is an obvious electron localized region between Rg and B,thus Rg-B should be partial covalent bond.Additionally,the insertion of Rg shortens the bond length of B-M and M-F' in FRgBMF2 and increases their bond order,which indicates that Rg plays a positive role in stabilizing the chemical bond of FBMF2.The structure and stability of rare gas-selenium/tellurium fluoride species FRgLFn(Rg=Kr Rn;L=Se and Te,n=1,3,5)as well as the corresponding cation FRgLFn-1+ were studied using theoretical methods.Five possible dissociation pathways of FRgLFn are discussed and the metastable character of FRgLFn is proved.NBO analysis and EDA show that FRgLFn can be expressed in the form of F-(RgLFn)+,that is,there is a strong ionic bond between F and Rg.However,there is partial covalent bond between Rg and L.The chemical properties of FRgL+ and FRgLF2+ are similar with FRgLFn,but FRgLF4+ is different from FRgL+ and FRgLF2+.In FRgLF4+,the orbital interaction of F-Rg bond is strong,so the F-Rg bond should be a covalent bond.However,Rg L bond should be an ionic bond with a smaller order and stronger electrostatic interaction.In addition,FKrSFn(n=1,3,5)and XXeSeFn(X=Cl,Br and I,n=1,3 and 5)are predicted to be stable.They show similar properties with FRgSe/TeFn,and further expand the species and quantity of rare gas-Se/Te compounds.A series of Rg inserted interhalogens FRgXFn(Rg=Kr-Rn,n=0 and 2)were investigated by DFT,MP2,and CCSD(T)with def2-TZVPPD basis set.There are two molecular structures of FRgXFn.Four possible dissociation paths are discussed for FRgXFn(three dissociation paths are discussed for FRgX).Meanwhile,the transition state of the reaction was found and the reaction energy barrier was summarized.For the F-Rg bond,the dissociation energies of FRgX and FRgXF2 are 179-188 kcal mol-1 and 162-175 kcal mol-1,respectively.The dissociation process is endothermic and nonspontaneous.The bond nature of Rg were analyzed by NBO,ELF and EDA The Wiberg bond index of F-Rg is only 0.2-0.3,and the electrostatic interaction accounts for 60%-70%of the total interaction energy.There is almost no region of electrons localized between F and Rg,so it is determined that F-Rg should be an ion bond.For the Rg-X bond of FRgX and FRgXF2,the Wiberg bond indices are between 0.72-0.81 and 0.54-0.74,respectively.EDA shows that the orbital interaction in the Rg-X bond is the main contribution to the total interaction,approximately 65%-79%.There is an electron localized region between Rg and X,so Rg-X has certain covalent properties.In addition,some other Rg inserted interhalogens,XRgX'(X=F and Cl;X'=F,Cl,Br and I)are identified and compared to extend this series of rare gas compounds.