Theoretical Studies On The Property Of Representative π-hole And Pseudo π-hole Pnicogen-Bonding Interaction

Noncovalent interactions play a vital role in molecular physics, molecular chemistry, molecular biology, material science, supramolecular chemistry, drug design, crystal engineering and so on. Recently, pnicogen bond has been recognized as a new type of noncovalent interaction. The pnicogen bond is also a Lewis acid-Lewis base attractive interaction in which a pnicogen atom(N, P, As or Sb) acts as the Lewis acid. Acting as a new molecular linker, the pnicogen bond will play an important role in material multi-level building, crystal engineering and supramolecular synthesis.In this work, we discussed the nature of π-hole and pseudo π-hole pnicogen bond, and the mutual influence between π-hole pnicogen bond and σ-hole halogen bond by the method of quantum chemistry calculation, the topological analyses of electron density, the electron localization function(ELF) theory, the natural bond orbital(NBO) and the molecular formation density difference(MFDD) method.1. The structures and properties of π-hole pnicogen-bonded complexes PO2X···PX3 and PO2X···PH2X(X = F, Cl, Br, CH3, NH2) were investigated by ab initio MP2/aug-cc-pVTZ calculations and topological analyses of electron density. The atoms-in-molecules(AIM), electron localization function(ELF) theory, noncovalent interaction(NCI) index method, natural bond orbitals(NBO) as well as the adaptive natural density partitioning(AdNDP) approach were used to expand the nature of the interactions considered. Two sets of π-hole pnicogen-bonded complexes were found on the potential surfaces. A-type complexes have P···P and type-B ones have P···X pnicogen bonds. The substituted groups strongly affect the properties of pnicogen bond interactions. Pnicogen bonds were covalent interactions for the electron-donating substituents(CH3、NH2), while they were noncovalent, partly covalent and covalent interactions when the substituents were electron-withdrawing groups. The larger the Wiberg bond order of the pnicogen-bonded interaction, the more covalent the bond and the greater its strength will be. In type-B conformations, charge transfer mainly occurs from an X lone pair of PX3/PH2 X molecule to the π*(P=O) orbital of PO2 X.2. The bimolecular and termolecular complexes involving PO2 Cl and XCN/C6H6(X = F, Cl, Br) were designed to form the π-hole pnicogen bonds and σ-hole halogen bonds, to compare the two types of interactions and investigate the mutual influences between them at the MP2/aug-cc-pVDZ level of theory. PO2 Cl was used as simultaneous π-hole and σ-hole donors, it can interact with electron donor to form π-hole pnicogen bond and σ-hole halogen bond. In terms of investigating the strength of interaction, electron density and charge transfer between electron donor and electron acceptor, the results indicated that the π-hole interactions are stronger than the σ-hole interactions, both in the bimolecular and the termolecular complexes. Comparing the cooperative effects of the π-hole interactions and σ-hole interactions, the π-hole interaction has a greater influence on the σ-hole interaction than vice versa. The π-hole pnicogen bond and σ-hole halogen bond weaken each other, i.e., there is a negative cooperative effect in most of the complexes.3. The pseudo π-hole in Group VA phosphorus compounds P3X3/As3X3(X = H, F, Cl, Br) were found. A detailed theoretical study of pseudo π-hole interaction HCN···P3X3/As3X3(X = H, F, Cl, Br) 、 hydrogen bond complexes P3X3/As3X3···NCH(X= F, Cl, Br) and the termolecular complexes HCN···P3X3/As3X3···HCN(X = F, Cl, Br) was performed at the MP2/aug-cc-pVDZ level. Electrostatic potentials, equilibrium geometries, interaction energies, topological properties of the electron densities, natural bond orbital and energy decomposition were investigated systematically. The results showed that pseudo π-hole interaction and hydrogen bond belong to the typical closed-shell noncovalent interaction. The most important factors for the pseudo π-hole interaction are the exchange and electrostatic energies, that is to say, the two interactions determined the stability of pseudo π-hole interaction. There have positive cooperativity between pseudo π-hole and hydrogen bond in the termolecular complexes HCN···P3X3/As3X3···HCN(X = F, Cl, Br).The innovations in this thesis:1. The ELF 、 NCI and AdNDP methods were effectively used to analyse the characteristics of pnicogen bond interaction which are noncovalent, partly covalent and covalent interactions.2. The pseudo π-hole region was firstly found in the molecules P3X3 and As3X3(X = H, F, Cl, Br), and the nature of pseudo π-hole interaction were discussed.