Study On The Structures And Properties Of Some Triel And Tetrel Bonds

This thesis has studied the structures and properties of the triel bond and tetrel bond in some selected systems.Themain results ofthis dissertation are asfollows:We studied the triel bond between ZX₃?Z=B and Al;X=H and Me?and THMe₃?T=Si,Ge and Sn?,and proposed the concept of triel-hydride triel bond.In THMe₃···BH₃,there occurs a proton transfer from the T–H bond to the triel atom,evidenced by the much shorter H···B distance,transformation of orbitalinteraction and large chargetransfer.What would be of some interest at this juncture would be a careful examination of tetrel bonding as it might relate to borazine.The former type of potential occurs in tetrahedral TH₃F?T=tetrel?molecules where the most intense?-hole is located directly opposite the T-F bond.The trivalent T atom in R₂T=O?R=H,F?has associated with it a pair of?-holes directly above and below the molecular plane.Of particular interest is the nature of the bonding in each configuration,with particular focus on the comparison of the?and?-hole bonded dimers.Also of concern is the comparison with othersorts ofbonds that might emerge including trielor H-bonds.There is a cooperative effect between triel bond and other types of interactions.In the ZX₃···NCM···C₂H₄?Z=B,Al;X=H,F;M=Cu,Ag,Au?system,there is positive cooperativity between the triel bond and regium bond,and the enhancement of triel bond is greater than that of regium bond.For the triad with positive cooperativity,the positive MEP becomes larger,and the CT in both regium bond and triel bond is increased.For the NCAu···C₂H₄···AlX₃?X=H,F?systems which is negative cooperativity between the triel bond and regium bond,both MEP and CT have a reverse change.Interestingly,the negative MEP on the C=C bond in both C₂H₄···AlX₃ and NCAu···C₂H₄ becomes positive but it is still able to engage in a regium bond with AuCN in the formerand a trielbond withAlX₃ in the latter.There also is cooperativity between triel bond and calcogen bond in the selected pyrazine,1,4-dicyanobenzene,and 1,4-benzoquinone as well as their derivatives,where the aromatic ring is at the center.We focus on the comparison of the strengths of triel bonding among these molecules,and interplay between triel bonding and chalcogen bonding.If the central molecule acts as a double Lewis base to bind with another two molecules,both interactions are weakened,and a larger weakening effect is found for thechalcogen bond.If the central molecule plays a dual roleof botha base in the triel bond and an acid in the chalcogen bond,both interactions are strengthened,and larger strengthening effect is found for the chalcogen bond.The cooperative mechanism of both the interactionsis mainly governed by electrostatic and chargetransfer effects.