Structures And Properties Of ?-hole And ?-hole Tetrel Bonds

In this thesis,the structures and properties of?-hole tetrel bond and?-hole tetrel bond are studied.The main results are as follows:?1?We chose F₂C=CFTF₃?T=C,Si,Ge?to provide?-hole and?-hole.The sp² hybridized C atom and the sp³ hybridized tetrel atom coexist in F₂C=CFTF₃,so it can be used as a model molecule to compare the intensities of?-hole and?-hole tetrel bonds.The Lewis bases we chose are three common small molecules:H₂CO,H₂O and NH₃.Most complexes are stabilized by tetrel bonds together with weak hydrogen bonds.The Lewis bases can be introduced to the?-hole and?-hole of F₂C=CFTF₃,but the?-hole bonded complexes are preferential for F₂C=CFTF₃?T=Si,Ge?,while the?-hole bonded complexes are favorable for F₂C=CFCF₃.Hybridization of the carbon atom adjoined with the SiF₃ group strengthens the?-hole tetrel bond in the order sp³<sp²<sp,similar to hydrogen and halogen bonds.The strength of?-hole tetrel bond is also dependent on the number,position,and conformation of substituents.In addition,solvents have a prominent enhancing effect on the strength of?-hole tetrel bond.?2?In this work,we studied the tetrel bond complexes of H₂CX?X=O,S,Se?and TH₃F?T=C,Si,Ge,Sn,Pb?and F₂TO?T=C,Si?related systems.H₂CX forms a?-hole tetrel bond with TH₃F and forms a?-hole tetrel bond with F₂TO.Generally,these complexes are combined with a primary tetrel bond and a weak H-bond.H₂CX is favorable to engage in the?-hole complex with F₂TO relative to TH₃F in most cases.Particularly,the double?-hole complex between F₂SiO and H₂CX?X=S,Se?has an interaction energy exceeding 500 kJ/mol,corresponding to a covalent-bonded complex with the huge orbital interaction and polarization energy.Both the?-hole interaction and the?-hole interaction are weaker for the heavier chalcogen atom,while the?-hole interaction involving F₂TO?T=Ge,Sn,Pb?has an opposite change.Both types of interactions are electrostatic in nature.?3?In the competition between?-hole tetrel bond and other interactions,we designed a complex of F₂C=CFZH₂?Z=P,As and Sb?with two Lewis bases?NH₃ and NMe₃?.In general,two minima complexes are found,one with a?-hole pnicogen bond and the other one with a?-hole tetrel bond in most complexes but two?-hole pnicogen bonded complexes are obtained for F₂C=CFZH₂ and NH₃.They have similar stability though F₂C=CFSbH₂ engages in a much stronger?-hole pnicogen bond with NMe₃.The-PF₂ substitution makes the?-hole on the terminal carbon form a tetrel bond with NH₃.A heavier-ZH₂ group engages in a stronger?-hole pnicogen bond but results in a weaker?-hole tetrel bond.Other than electrostatic interaction,the stability of both complexes is attributed to the charge transfer from the N lone pair into the C–Z/H–Z anti-bonding orbital in the pnicogen bond and the C=C anti-bonding orbital in the tetrel bond.