Theoretical Studies Of Weak Interaction Systems Containing Various Electron Donors

Due to the extensive application of weak interaction in many research fields,the structures,properties,and nature of the interaction of related systems have been paid much attention.In this paper,three types of weak interactions where radicals,conjugated molecules,and lone pair serve as electron donors,respectively,have been studied in detail by quantum chemical methods.The geometrical structure,properties and interaction nature of the resulting system have been systematically examined.In this thesis,a new type of weak interaction,namely single-electron magnesium bond,has been proposed.And then,multibody complexes formed between a conjugated molecule and multiple magnesium/beryllium salt molecules have been studied in detailed.Besides,the non-covalent interaction system of superalkali metal cation Li₃⁺binding multiple N₂ligands has been investigated.The main contributions of this thesis are as follows:1.The complexes formed between Mg X₂(X=F,H)molecules and alkyl radicals Y[Y=CH₃,CH₂CH₃,CH(CH₃)₂,and C(CH₃)₃]have been characterized by using quantum chemical methods.The binding distances in all cases are shorter than the sum of vd W radii of Mg and C,indicating the formation of a non-covalent interaction,namely single-electron magnesium bond.Energy decomposition analysis reveals that electrostatic and polarization contributions are the major components responsible for the stability of the studied complexes.According to interaction energy,atoms in molecules,and independent gradient model analyses,methyl substitution on electron donor Y imposes a positive effect on its complexation with Mg X₂.When compared with other nonbonded interactions,single-electron magnesium bond is found to have strength comparable to those of single-electron beryllium bond and?-magnesium bond.2.To reveal the diversity of interaction sites between?-conjugated and Lewis acid molecules and compare the electron-donating ability of different Lewis bases,we have studied the geometric structures and related properties of the n X₂M···Y[n=1,2,3,4;X=F,H;M=Be,Mg;Y=C₂H₂,C₂H₄,C₆H₆]complexes.Results indicate that acetylene possesses better electron-donating performance than ethylene and benzene.And only the C₂H₂molecule can bind with three independence Be H₂/Be F₂molecules.The RDG results indicate that there is intermolecular interactions between each Lewis acid and Lewis base molecule in all cases.The results of interaction energy of the3X₂M···C₆H₆complexes show that para-position is the preferred relative location of two Lewis acid subunits.NBO analysis reveals that the main charge-transfer arises from the?_CCbonding orbital of the conjugated molecule to the empty 2p orbital of Be atom or 3p orbital of Mg atom.AIM analysis,which serves as an effective method to describe bonding character,has revealed that the MX₂and Y subunits are mainly connected by ring path(RP)and bond path(BP)in the studied?-Be and?-Mg complexes.3.The potential of superalkali cation Li₃⁺for capturing N₂and its behavior in gaseous nitrogen have been theoretically studied at the MP2/6-311+G(d)level.Evolution of structures and stability of the Li₃⁺(N₂)_n(n=1-7)complexes shows that the N₂molecules tend to bind to different vertices of the Li₃⁺core,and that Li₃⁺might have the capacity to capture up to twelve nitrogen molecules in the first coordination shell.Based on natural population and molecular orbital analyses,Li₃⁺keeps superatom identity in the lowest-lying Li₃⁺(N₂)_n(n=1-4)complexes.The change in Gibbs free energies of possible fragmentation channels also indicates thermodynamic stability of Li₃⁺in the(N₂)_nclusters when n?4.Different from the case of Li₃⁺(H₂O)_nwhere the electrostatic interaction is dominant,the electrostatic and polarization components are found to make nearly equal contributions to the Li₃⁺(N₂)_ncomplex formation.In addition,it can be concluded that superalkali cation Li₃⁺surpasses heavy alkali metal cations in capturing N₂molecules since it has larger binding energy with N₂than Na⁺and K⁺ions.