Theoretical Study On The Structures And Properties Of Some Hydrogen/pnicogen/tetrel-bonded Complexes

In this thesis,the formation,properties,and,nature of hydrogen,pnicogen,and tetrel bonds have been studied by means of theoretical calculations.The main contents are summarized as follows:We performed a systemic investigation of the substitution and cooperative effects on the O-H···O and N-H···O H-bonds in the complexes of 2-pyridone and its derivatives with oxalic acid.Generally,the electron-withdrawing substituent?-NO₂ and-F?in 2-pyridone weakens the O-H···O H-bond but strengthens the N-H···O H-bond,while the electron-donating group?–NH₂ and–CH₃?brings out a reverse effect on both H-bonds.In addition,the substitution effect is also dependent on its substitution position in 2-pyridone.When oxalic acid combines with two 2-pyridone/2-pyridinethione molecules,the O–H···O/S H-bond is weakened but the N–H···O H-bond is enhanced.When three oxalic acid molecules are linked by the double O–H···O H-bonds,one H-bond with the middle oxalic acid as the proton donor is weakened and the other H-bond with the middle oxalic acid as the proton acceptor is strengthened.The properties and nature of pnicogen bond were discussed in PyZX₂?Py=pyridine,Z=P,As;X=H,F?and its protonation.The relative stability of pnicogen-bonded complexes is related to the nature of PyZX₂ and bases.When the nitrogen atom of PyZX₂is protonated,the protonated complexes are more stabilized,the interaction energies increased by 8.5³4.6 kJ/mol.In the neutral complexes of PyZX₂ and H₂O,the N···H-O is favorable compared to the pnicogen bond.Such inclination is more prominent in the complexes of protonated PyZX₂ and NH₃.Pnicogen bond is more strengthened or weakened due to positive/negative synergistic effects in H₂O···PyZX₂···H₂O or NH₃···H⁺-PyZX₂···NH₃,respectively.A computational study of an intramolecular tetrel bond in omethoxymethyl-PhSiF₃?P?and its derivatives has been performed.Substituents do not greatly affect the strength of intramolecular Si···O interaction.The interation energy has been computed with three methods and the most reliable results is obtained with an expression using the potential energy density at the critical point of Si···O bond.The interaction energy of intramolecular Si···O up to 12 kcal/mol with the cooperation of OH···F,when a water molecule is attached to P.F₂TO?T=C and Si?can form tetrel bonds with malondialdehyde?MDA?.The action of F₂SiO is stronger than F₂CO.The?-tetrel bond strengthens/weakens the intramolecular hydrogen bond of MDA when the bond is formed to hydroxyl/carbonyl group of MDA,and causes an accompanying inhibition/promotion of proton transfer within this H-Bond,respectively;the stronger influence is for F₂SiO.A new?-?tetrel bond is found when F₂TO stack directly above the MDA plane.At the same time,we can regulate the intramolecular hydrogen bonds by the substituents.The effects of tetrel bond,solvation,and ionization on the configuration of glycine have been compared,and the configuration is stabilized by regulating the intramolecular proton transfer of glycine.It was found that the tetrel bond formed by glycine and F₂TO?T=C,Si?has the largest effect,followed by solvent effect and ionization.