Theoretical Study Of Regulation Of Tetrel Bonding Strength And -TX₃ Group Transfer

Tetrel bond is a noncovalent interaction which occurs between a?-hole/?-hole on the IV atom and an electron donor,and it has extensive applications in the fields of crystal engineering,chemical reactions,molecular recognition,and biological systems.In this thesis,ab initio calculations are thus utilized to study one?-hole tetrel-bonded and three?-hole tetrel-bonded complexes.By means of substitution,cooperativity,and an external electric field,the tetrel bond is strengthened and thus a transfer of-TX₃ group is realized.The main results are as follows:The ?-hole above the plane of the X₂T'Y molecule(T'=Si,Ge and Sn;X=F,Cl and H;Y=O and S)with TH(CH₃)₃(T=Si,Ge and Sn)TH of a molecule can form a tetrel bond.The obtained TH···T'has a very strong effect,and its effect energy exceeds 30 kcal/mol.Compared with F₂T'S,Cl₂T'O and Cl₂T'S,the effect of F₂T'O formation was the strongest.This effect decreases in the order of T'=Si>Ge>Sn,but the?-holes on T'increase.Although the negative electrostatic potential value around H in Lewis base TH(CH₃)₃ is almost independent of T,larger T forms stronger tetrel bonds.When a H₂O molecule interacts with the F₂T'O complex,there are two situations:one is when the O atom of H₂O forms a tetrel bond with another?-hole of F₂T'O,and the original tetrel bond is weakened.The second case is that an H atom of this H₂O molecule forms a hydrogen bond with the O atom of F₂T'O,and the T tetrel bond will be strengthened.Ab initio calculations are performed for the binary and ternary complexes of Sp CO₃/Sp SO₄/Sp Cl₂(Sp=Zn(?),Cd(?))as molecules that can engage in both a spodium bond through spodium(Sp)or a tetrel bond through O or Cl.NCH,NHCH₂,and NH₃ are considered as Lewis bases with widely varying nucleophilicity.The Sp···N spodium bonds are very strong,with interaction energies in the 12?59 kcal/mol range.Those bonds involving Zn are somewhat stronger than Cd,and bond strength diminishes in the SO₄>CO₃>>2Cl ligand order.tetrel bonds between the Si of SiH₃F and a O or Cl atom of the ligand are of moderate strength of 2?9 kcal/mol.In ternary complexes in which both a spodium and tetrel bond are simultaneously present,there is a positive cooperativity between them.The bond enhancement is particularly significant in the tetrel bond,whose strength can reach as much as 15 kcal/mol within the ternary complexes.The modulation of substituents,cooperativity,and electric field on tetrel bond strength is investigated.T···N tetrel bonds that TX₃OH(T=C,Si and Ge;X=H and F)can form with Lewis base N?CM(M=H,Li and Na).Complexes involving TH₃OH contain a conventional tetrel bond with interaction energy less than 10 kcal/mol.This bond is substantially strengthened,approaching35 kcal/mol and covalent character,when fluorosubstituted TF₃OH is combined with NCLi or NCNa.Along with this enhanced binding comes a near equalization of the tetrel bond T···N and the internal T-O bond lengths,and the associated structure acquires a trigonal bipyramidal shape,despite a high internal deformation energy.This structural transformation becomes more complete,and the tetrel bond further strengthened,upon adding an electron acceptor Be Cl₂ to the Lewis acid and a base to the NCM unit.This same tetrel bond strengthening can be accomplished also by imposition of an external electric field.The possibility of the transfer of the-TH₃ group across a tetrel bond in M···Ph TH₃···N-base(M=Be²⁺and Mg²⁺;Ph=phenyl;T=Si and Ge;N-base=NH₃,NHCH₂ and C₃N₂H₄)system is considered by ab initio calculations.The-TH₃ moves toward the base but only by a small amount in these dimers.However,when a Be²⁺or Mg²⁺dication is placed above the phenyl ring,the tetrel bond strength is greatly magnified reaching up to nearly 100 kcal/mol.This dication also induces a much higher degree of transfer which is half transfer for NH₃ and NHCH₂ bases,and full transfer for N-heterocyclic carbene.