Theoretical Study On The Structures And Properties Of Some Tetrel-bonded Complexes

This thesis has studied a novel kind of intermolecular interaction-tetrel bonding since it has potential applications in crystal materials,chemical reactions,and biological systems.In this dissertation,theoretical calculations have been performed for the structures,properties,nature,application and modulation of tetrel bonds in some important systems.The main results of this dissertation are summarized as follows:Carbenes and pseudohalide anions?N₃-/OCN-/SCN-?are used to form tetrel bonds as Lewis bases,thus the carbene tetrel bond and pseudohalide anion tetrel bond are proposed,respectively.Stabilization of these complexes mainly depends on the nature of tetrel atoms and Lewis bases.Interestingly,tetrel bond becomes stronger in the order of T = C<Ge<Sn<Si in TH₃F…NHC.The tetrel bond is dominated by electrostatic interaction,while orbital interaction also makes an important contribution.Formation of the tetrel bond is mainly attributed to charge transfer from the lone pair in the Lewis bases into the T-Y and T-H anti-bonding orbitals in the strong tetrel bond,and the former orbital interaction is responsible for the large elongation of T-F bond and the remarkable red shift of its stretch vibration.Substitution and hybridization can modulate the strength of tetrel bond.The electron-withdrawing group in the tetrel donor strengthens the tetrel bond,while that in the tetrel acceptor weakens the tetrel bond.The electron-donating group in the Lewis bases enhances the tetrel bond,and this effect is mainly achieved through electrostatic and polarization interactions.The tetrel bond becomes stronger in the order p-PySiF₃…NCH?sp?</p-PySiF₃…NHCH₂?sp2?<p-PySiF₃…NH₃?sp3?.There is cooperativity between tetrel bond and other interactions.The carbene tetrel bond can be strengthened by the cooperative effect with the N…M interaction in trimers H₂C…CH₃CN…M?M = CH₃CN,HCN,ICN,SbH₂F,LiCN,and BeH₂?and is doubled in H₂C…CH₃CN…BeH₂.Cooperativity between the tetrel bond of PySiX3 with a series of nitrogenated bases and the triel/chalcogen bond of PySiX3 with three molecules having?-hole?BF₃,BCl3,and SO3?has been studied.Tetrel bonding displays cooperative effect with triel/chalcogen bonding and this effect is mainly caused by polarization energy.The ternary complexes BeH₂…XTH₃…NH₃?X = F,Cl,and Br;T = C,Si,and Ge?have been studied to explore the cooperativity between tetrel bond and beryllium bond.In the ternary systems,both the beryllium bond and the tetrel bond are enhanced,and the tetrel bond has greater enhancement than the beryllium bond,which is mainly ascribed to the increase of both electrostatic potentials on the corresponding atoms and charge transfer.The protonation has a significant influence on the tetrel bond.The primary interaction mode between ?/?-furanCF₃/p-PyCF₃ and NH₃ changes from a F…H hydrogen bond to a C…N tetrel bond as a result of protonation.The protonation has a prominent enhancing effect on the strength of tetrel bonding with an increase of interaction energy from-14.15 kcal/mol to-30.09 kcal/mol.The tetrel bonding becomes stronger in order of H+-p-PySiF₃…NH₃<H+-m-PySiF₃…NH₃<H+-o-PySiF₃…NH₃,showing a reverse trend with that of the neutral analogues.Tetrel bond plays a very important role in the S_N2 reaction.It is a preliminary stage of the N₃-+ CH₃Br ? Br-+ CH₃N₃ reaction and a posterior stage in the reaction F-+ CH₃N₃?N₃-+ CH₃F.