Theoretical Study Of Dihydrogen Bonds Of NH₃BH₃,NH₃AlH₃ And NH₃GaH₃ With Several Small Molecules

In present paper,ab initio quantum mechanics method is employed to investigate the origin of red-shifting and blue-shifting dihydrogen bonds between NH₃BH₃,NH₃AlH₃,NH₃GaH₃ and several small molecules.The main contents are the following:1.The bifurcated dihydrogen bonds B-H₂…H-X(X=C,N) of NH₃BH₃ with CHF₃,H₂CO, HCOOH,HCOCl and HNO have been theoretically stduied.The results show that the dihydrogen H-bond leads to red shift of the B-H bond and blue shift of the X-H bond.The blue shift of the X-H bond is caused by decrease of the intramolecular hyperconjugation,positive repolarization and positive rehybridization of the X-H bond,and the bent configuration of the bifurcated dihydrogen bond;the red shift of the B-H bond are caused mainly by negative replorization and negative rehybridization of the B-H bond.2.The dihydrogen bonds B-H…H-X(X=F,Cl,Br,C,O,N) in the dimer(NH₃BH₃)₂ and the complexes of NH₃BH₃ with HF,HCl,HBr,H₂O and CH₃OH have been theoretically studied.The results show that formation of the dihydrogen bond leads to elongation and stretch frequency red shift of the B-H and X-H bonds.For(NH₃BH₃)₂ and the complexes of the halogenides,red shifts of the X-H bonds are caused by the intermolecular hyperconjugationσ(B-H)→σ^*(X-H);in the other two systems,the red shift of O-H bond is a secondary effect of the stronger traditional red-shifted H-bonds N-H…O.In all these systems,red shifts of the B-H bonds are caused by the two factors: negative reploarization and negative rehybridization of the B-H bond,and decrease of occupancy onσ(B-H) caused by the intermolecular hyperconjugationσ(B-H)→σ^*(X-H).3.The dihydrogen bonds Al-H…H-X(X=F,Cl,Br,C,O) of NH₃AlH₃ with HF,HCl,HBr,H₂O, CH₃OH,H₂CO and HNO,have been theoretically stduied.The results show that the dihydrogen H-bond leads to red shifts of Al-H and X-H bonds(in the H₂CO and HNO system,C-H and N-H bonds blue shift).For(NH₃AlH₃)₂ and the complexes of the halogenides,the red shifts of X-H bonds are caused by the intermolecular hyperconjugationσ(Al-H)→σ*(X-H);for the systems of H₂CO and HNO,the blue shift of C-H is caused by decrease of the intramolecular hyperconjugation n(O)→σ^*(C-H,N-H);in the other systems,the red shift of X-H bond is a secondoary result of the stronger traditional red-shifted H-bonds N-H…X.In all these systems,the red shifts of Al-H bonds are caused by the two factors:negative replorization and negative rehybridization,and decrease of occupancy onσ(Al-H) caused by the intermolecular hyperconjugationσ(Al-H)→σ^*(X-H).4.The dihydrogen bonds Ga-H…H-X(X=F,Cl,Br) of NH₃GaH₃ with HF,HCl and HBr have been theoretically studied.The results show that the dihydrogen H-bond leads to red shifts of Ga-H and X-H bonds.The red shifts of X-H bonds are caused by the intermolecular hyperconjugationσ(Ga-H)→σ^*(X-H);the red shifts of Ga-H bonds are caused by the two factors:negative replorization and negative rehybridization,and decrease of occupancy onα(Ga-H) caused by the intermolecular hyperconjugationα(Ga-H)→σ^*(X-H).