Structures And Properties Of σ-hole And π-hole Tetrel Bonds

In this thesis,the structures and properties ofσ-hole tetrel bond andπ-hole tetrel bond are studied.The main results are as follows:（1）We chose F₂C=CFTF₃（T=C,Si,Ge）to provideσ-hole andπ-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 ofσ-hole andπ-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 theσ-hole andπ-hole of F₂C=CFTF₃,but theσ-hole bonded complexes are preferential for F₂C=CFTF₃（T=Si,Ge）,while theπ-hole bonded complexes are favorable for F₂C=CFCF₃.Hybridization of the carbon atom adjoined with the SiF₃ group strengthens theσ-hole tetrel bond in the order sp³<sp²<sp,similar to hydrogen and halogen bonds.The strength ofσ-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 ofσ-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 aσ-hole tetrel bond with TH₃F and forms aπ-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 theπ-hole complex with F₂TO relative to TH₃F in most cases.Particularly,the doubleπ-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 theσ-hole interaction and theπ-hole interaction are weaker for the heavier chalcogen atom,while theπ-hole interaction involving F₂TO（T=Ge,Sn,Pb）has an opposite change.Both types of interactions are electrostatic in nature.（3）In the competition betweenπ-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 aσ-hole pnicogen bond and the other one with aπ-hole tetrel bond in most complexes but twoσ-hole pnicogen bonded complexes are obtained for F₂C=CFZH₂ and NH₃.They have similar stability though F₂C=CFSbH₂ engages in a much strongerσ-hole pnicogen bond with NMe₃.The-PF₂ substitution makes theπ-hole on the terminal carbon form a tetrel bond with NH₃.A heavier-ZH₂ group engages in a strongerσ-hole pnicogen bond but results in a weakerπ-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.