Theoretical Investigations On The Structure And Stability Of Tin,Lead-related Cyanides

Metal cyanide/isocyanide and hydrometal cyanide/isocyanide compounds are the key metal-carriers in interstellar space.Lighter group 14 elements（X=C/Si/Ge）cyanides/isocyanides and hydrocyanides/hydroisocyanides have been studied theoretically or experimentally.However,no reports are available on the analogues of tin（Sn）and lead（Pb）.In this paper,we carried out the first theoretical study on the structures and stabilities of[X,C,N]and[H,X,C,N]（X=Sn/Pb）at the CCSD（T）/def2-QZVPP//B3LYP/def2-QZVPP level.The chemical evolution processes of these Sn,Pb-related isomers are described in detail by using our locally developed the grid-based comprehensive isomeric search strategy and global potential energy surface survey（GPESS）”methods.Comparisons were made with the lower analogues（X=C/Si/Ge）concerning the structural,energetic and bonding properties in this paper.The main contents are summarized as follows:1.Significantly different from that of c-C₂N,a dative-bonded valence structure of c-XCN for heavier X was revealed for the first time,which can well account for the rather worse kinetic stability of cyclic[X,C,N]for heavier X=Si/Ge.2.The RNC?RCN conversion barriers are strongly correlated with the bonding energy of R-NC.The higher the bonding energy（R-NC）is,the higher the conversion barrier is.3.A unique kind of agostic bonding was found within three isomers of [H,Pb,C,N],whereas it is absent for X=C/Si/Ge/Sn.4.Combined with previous experimental synthesis studies and our potential energy surfaces analysis,we predicted that isomers XCN ²1,XNC ²2,HXCN¹1,HXCN ¹2,HCNX ³3,HNCX ³5,c-XCHN ¹7 and c-XCNH ¹8 are potential candidates for future laboratory and astrophysical detection.The calculated structures and spectroscopic properties are expected to stimulate future characterization of the metals cyanides/isocyanides and hydrometal cyanides/isocyanides both in laboratory and in interstellar space.