Theoretical Studies On Weakly Bound Electrons Enhancing Nuclear Spin Coupling In Fluorocarbon Compounds

Small sizes of cyclic and cage-shaped alkanes,as well as polyhedral alkanes,have attracted great interest and attention in the chemical community due to their good molecular symmetry and unique physical and chemical properties.Perfluorination can have a profound impact on these alkanes,and small sizes of cyclic and cage-shaped perfluoroalkanes,as well as polyhedral fluorocarbons,exhibit the strong ability to bind an additional electron.An additional electron combines with these fluorocarbons to form stable solvated electron systems.Unlike strongly bound electrons（i.e.bonding electrons or lone pair electrons）in traditional strongly electron systems,solvated electrons in solvated electron systems are weakly bound electrons with distinct dispersion and Rydberg characters.Up to now,there have been many studies on the structures,properties and applicatons of solvated electron systems,however,there are few studies on the characters of solvated electrons captured by fluorocarbons and how solvated electrons regulate the nuclear spin-spin coupling properties.This paper mainly explores the states,distributions and properties of solvated electrons in fluorocarbon solvated electron systems through density functional theory,electron localization function analysis,and natural bond orbital analysis,and reveals the mechanisms and rules of solvated electrons regulating the nuclear spin-spin coupling of fluorocarbons.The main conclusions and innovations are as follows:（1）Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes:Small sizes of cyclic perfluoroalkanes(c-C_nF_2n（n=3,4,5）)and cage-shaped perfluoroalkanes（C_nF_n（n=4,6,8））can capture an additional electron to form solvated electron systems.Reasearch has found that the special distributions of solvated electrons on C-C bond（bonding character distribution）and C-F bond（antibonding character distribution）results in the general change in the C-C bond shortening and C-F bond elongating of small sizes of perfluorocycloalkanes and cage-shaped perfluoroalkanes.In addition,as strong intervening electrons,solvated electrons can abnormally enhance NeJFF.Improtantly,solvated electrons with special distributions,states and properties trigger a novel coupling transmission mechanism based on solvated electron（esolbased）,which is different from traditional "through-bonds（T-B）" and "through-space（T-S）"coupling transmission mechanisms,including two coupling paths:"through-solvated electron（T-SE）" coupling path and "solvated electron enhanced T-B and T-S（esol--enhanced T-B⊕T-S）"coupling path.The influencing factor of T-SE coupling is the angle of coupling path,while the influencing factor of esol--enhanced T-B⊕T-S coupling is the distance of coupling path.With the increase of the number of chemical bonds on the shortest T-B coupling path,T-SE coupling gradually dominates.The two coupling paths jointly realize and regulate the large NeJFF through competition and cooperation.This work not only enriches the understanding of the coupling mechanism in weakly bound electron systems,but also provides useful information for the design of F-NMR probes in atmospheric diffusion research and the design of esol--based electronic devices.（2）Unusual J-Couplings through Solvated Electron in Perfluoro-[n]Prismanes and[n]Asteranes:Perfluoro-[n]prismanes（（C₂F₂）_n,n=3-8）and[n]asteranes（（C₃F₄）_n,n=3-5）exhibit a strong perfluoro cage effect,that is,they can stably encapsulate an additional electron within the cage,and then capture an additional electron to form polyhedral fluorocarbon solvated electron systems.Reasearch has found that the ground-state orbitals of solvated electrons exhibit a 2s-like type characteristic distribution in prism-shaped e@（C₂F₂）_n（n=3-8）and aster-shaped e@（C₃F₄）_n（n=3-5）,mainly due to unique polyhedral structure that allows solvated electrons to penetrate the C-shell and C-F bond regions,extending and modifying the tail of solvated electron orbitals.The 2s-like type distribution of solvated electrons triggers a novel coupling mechanism based on solvated electron（esol--based）,including two coupling paths:"through-solvated electron（T-SE）" coupling path and "solvated electron enhanced T-B and TS（esol--enhanced T-B⊕T-S）" coupling path.Significantly,when the angle（∠F?F）between two coupled F nuclei and the polyhedral center is smaller than 70°,the number（N）of chemical bonds in the shortest T-B coupling path is 3 or 4,and the spatial linear distance(d_FF)between two coupled F nuclei is short.And the contribution（JTB+TS）of esol--enhanced T-B⊕T-S coupling determines the sign,absolute value and change character of ^N（e）J_FF.In this case,the sign of ^N（e）J_FF is negative and |^N（e）J_FF| decreases with the increase of ∠F?F and d_FF.When ∠F?F is larger than 70°,N is 4 or>4 and d_FF is long,the contribution（JT-SE）of T-SE coupling determines the sign,absolute value and change character of ^N（e）J_FF.In this case,the sign of ^N（e）J_FF is positive and |^N（e）J_FF| increases with the increase of ∠F?F and d_FF.This work further not only enriches the information about the states,distributions and properties of solvated electrons,but also provides insights into the nuclei spin properties triggered or improved by solvated electrons in fluorocarbon compounds.In summary,in this paper,density functional theory,electron localization function analysis and natural bond orbital analysis were utilized to systematically explore the molecular structures,electronic properties and electronic effect of small sizes of cyclic and cage-shaped perfluoroalkanes,as well as perfluoro-[n]prismanes and perfluoro-[n]asteranes solvated electron systems.This paper revealed the mechanisms and rules of solvated electrons regulating indirect fluorine nuclear spin-spin coupling,providing theoretical bases for the application of solvated electron systems in the practical field of nuclear magnetic resonance probes.