Theoretical Studies Of The Pnicogen Bond And Halogen Bond

Intermolecular interactions have attracted substantial interest in recent years since these interactions are of vital importance in material chemistry, crystal engineering and biological systems. These interaction usually referred to hydrogen bond, halogen bond, pnicogen bond, cation-π, anion-π and so on. The formation of these noncovalent interactions can be rationalized on the basis of two computational finds. (1) The presence of a small positive electrostatic potential end cap along the A-X bond vectors. (A usually refer to electronegative atoms/groups) In recent articles, the positive cap of halogen atoms was referred to as the a-hole. The same concept has now been extended to some atoms of group V and VI (pnicogen bond and chalcogen bond) to elucidate their ability to form directional noncovalent interactions. (2) The anisotropic distribution of electron density around halogen atoms that there are two different radii of halogens:a shorter one along the A-X bond and a longer one perpendicular to it. Of particular interest is that halogens exhibit both electrophilic character along the axes of the A-X bonds and nucleophilic character along the vectors that are perpendicular to these bonds, In this paper we studied the pnicogen bonds and halogen…halogen bond based on these characters of halogen bond.The research contents and conclusions are summarized in the following section:1. In order to use polarizable ellipsoidal force field (PEff) which ever used for halogen bond to pnicogen bond, we should analyze the difference between the two intermolecular interactions. Firstly, the nature of these interaction are the same that halogen atom or pnicogen atom interact with electronegative group which referred as donor-acceptor interaction. In addition, there is now general agreement that the attractive nature of these interactions is primarily ascribed to electrostatic effects, but polarization, charge transfer and dispersion contributions all play an important role. And the polarizable ellipsoidal force field could reproduce pnicogen bond potential energy surface (PES). But there are three substituent group not one connect with covalent pnicogen atom directly. And they are all contribute to the electron density around pnicogen atom so that the angle of a-hole is not 180°but about 170°. Here we define a vector K (k1, k2, k3) which is determined by the three substituent group of pnicogen atom to represent the angle of a-hole.2. The electrostatic potential is highly anisotropic which made electrophilic character along the A-X vectors and nucleopilic character perpendicular to the A-X vectors. This could interpret dimer or triangular halogen…halogen nonbonding interaction. Halogen…halogen interaction are very important in self-assembly process, crystal engineering and biological recognition. It is hardly to use other method but density functional theory (DFT) for these system. But DFT method could not explain explicit electronic correlation. The performance of several density functional theory (DFT) methods has been evaluated comparing the results with those obtained from second-order M(?)ller-Plesset perturbation (MP2) and coupled cluster with single, double, and noniterative triple excitations (CCSD(T)) with complete basis sets (CBS).