The MP2 ab initio quantum chemistry methods were utilized to study the halogen-bond and pnicogen-bond system formed between PH 2 X (X 5 Br, CH 3 , OH, CN, NO 2 , CF 3 ) and BrY (Y 5 Br, Cl, F). Calculated results show that all substituent can form halogen-bond complexes while part substituent can form pnicogen-bond complexes. Traditional, chlorine-shared and ion-pair halogenbonds complexes have been found with the different substituent X and Y. The halogen-bonds are stronger than the related pnicogen-bonds. For halogen-bonds, strongly electronegative substituents which are connected to the Lewis acid can strengthen the bonds and significantly influenced the structures and properties of the compounds. In contrast, the substituents which connected to the Lewis bases can produce opposite effects. The interaction energies of halogen-bonds are 2.56 to 32.06 kcalÁmol 21 ; The strongest halogen-bond was found in the complex of PH 2 OH···BrF. The interaction energies of pnicogen-bonds are in the range 1.20 to 2.28 kcalÁmol 21 ; the strongest pnicogen-bond was found in PH 2 Br···Br 2 complex. The charge transfer of lp(P) Ar*(BrAY), lp(F) Ar*(BrAP), and lp(Br) Ar*(XAP) play important roles in the formation of the halogen-bonds and pnicogen-bonds, which lead to polarization of the monomers. The polarization caused by the halogen-bond is more obvious than that by the pnicogen-bond, resulting in that some halogenbonds having little covalent character. The symmetry adapted perturbation theory (SAPT) energy decomposition analysis showes that the halogen-bond and pnicogen-bond interactions are predominantly electrostatic and dispersion, respectively.
K E Y W O R D Sab initio calculation, halogen-bond, interaction energy, pnicogen-bond, symmetry adapted perturbation theory 1 | I N TR ODU C TI ON Noncovalent interactions often play an important role in the stabilization of macromolecular, such as proteins and nucleic acids. Typically, noncovalent interactions include van der Waals forces, electrostatic interactions, hydrophobic interactions, and hydrogen bonds, in which the hydrogen bonding has been extensively investigated partially due to its high importance in systems involving water molecules. There are still some other types of noncovalent bonding, such as halogen bonding and lithium bonding. [1] These interactions have some similarities to the hydrogen bonding, but the details are not very clear and much effort has been put into revealing the nature of these interactions during the past decades. In our previous Int J Quantum Chem. 2017;117:e25443.