A Computational Study Of Pnicogen Bonding Interaction In XH₂P…HBeY Complexes

In this paper, we employed ab initio to study pnicogen-hydride interaction in complexes XH2P…HBeY. comparative study of various weak interactions in the systems FH2P…HBeY and Pnicogen bonds:complexes between +XH3P and HBeY systems. For several types interaction were found, i.e., pnicogen…H, pnicogen…Y and pnicogen-Be interaction. there are other types of intermolecular interactions and system studies of the formation mechanism of these interactions. The main contents include the following three parts:1. The pnicogen-hydride interaction in the complexes XH2P…HBeY (X= F. Cl and Br; Y=H. F. Cl, Br, and CH3) has been studied and characterized using ab initio quantum chemistry methods. P in XH2P and H in HBeY act as Lewis acid and base respectively. Calculation indicates that the interaction between XH2P and HBeY is strong, comparable with typical hydrogen bonds; the calculated binding energies with BSSE correction by MP4(SDQ)/aug-cc-pVTZ vary from the least 13.29 kJ/mol of BrH2P…HBeF to the largest 45.63 kJ/mol of FH2P…HBeH. The binding energy increases with the acidity of P and the basicity of HBeY. An electron-withdrawing substituent X will enhance but an electron-withdrawing substituent Y will weaken the pnicogen-hydride interaction. Theory of atoms in molecules, natural bond orbitals and natural resonance theory, molecular electrostatic potential and localized molecular orbital energy decomposition analysis were applied to investigate the pnicogen-hydride bonds. A double-way charge transfers and intermolecular hyperconjugations from Lp(P) to σ*(HBe) and from σ(HBe) to σ*(XP) mainly contribute to the stability and bonding of the complexes.2. A theoretical study of the complexes formed between FH2P and HBeY (Y= F, Cl and Br) has been carried out using ab initio methods (MP2/aug-cc-pVDZ. MP2/aug-cc-pVTZ and MP4(SDQ)/aug-cc-pVTZ). For each system six local energy minima were found, i.e., a pnicogen…H complex, a pnicogen…Y complex, one pnicogen…Be complex, two Be…F complexes and a pnicogen-H…H complex. The pnicogen…H and one pnicogen…Be interactions are the strongest but the pnicogen-H…H dihydrogen bond is the weakest. The strongest interaction is the P…Be bonding in FH2P…HBeBr complex with an interaction energy -40.98 kJ/mol and a binding distance P…Be 2.2 A. Theory of atoms in molecules, natural bond orbitals analysis, molecular electrostatic potential and energy decomposition analysis were applied to investigate these various weak interactions.3. The interaction in the complexes +XH3P(X= F, Cl and Br) and HBeY(Y= H, F, Cl, Br and CH3) has been studied and characterized using ab initio quantum chemistry methods. For each system two interactions were found, i.e., pnicogen…H and pnicogen…Y interaction. For the same complex, pnicogen…H bonding interaction is greater than the pnicogen…Y bonding interaction. A charge transfers and intermolecular hyperconjugations from a(BeH) to σ*(PX) for pnicogen…H complexes and from Lp(Y) to σ*(PX) for pnicogen…Y complexes. The comparison of the properties of the neutral XH2P:HBeY and the protonated +XH3P:HBeY dimers shows some similar features (distance and interaction energy) but +XH3P:HBeY system than XH2P:HBeY system more stable.