Comparative Studies On Group Ⅲ σ-hole And π-hole Interactions

Diborane has long been of interest to chemists because of its unusual structure and bonding, it is very useful in many synthetic applications, electrics industry, crystal engineering, and so on. In recent years, the σ-hole and π-hole concept is limited to explain the covalent-bonded atoms of groups IV-VII. So we choose the molecule containing group IIIA atoms as the object of study. The focus of this study is the bridged-hydrogen structure of diborane and the σ-hole and π-hole interaction.First, our interest of this research is on the Hb atoms of B2H6, to investigate the character of the Hb···N hydrogen-bonded interaction, and how to strengthen the electron-accepting ability of the Hb atoms and further enhance the hydrogen bond between the Hb atoms and NH3. Then we get the nature of σ-hole and π-hole interaction which containing the group IIIA elements. All complexes were fully optimized with the Gaussian 09 program package. the electrostatic potentials were calculated on the 0.001 a.u.(electrons/bohr3) contour of the molecule’s electronic density with the WFA surface analysis suite. QTAIM analysis were carried out with AIMALL professional software. The interaction energies were decomposed by means of the LMOEDA method with the GAMESS program. The density difference in molecular formation was analyzed using Multiwfn software. This paper is divided into the following several parts:(1) The character of the bridged hydrogen atom(Hb) of B2H6 has become a hot issue in recent years. In this work, the complexes B2H6···NH3,B2H2X4···nNH3(n = 1, 2) and 2HF···B2H2X4···2NH3(X = Cl, Br, I) were constructed and studied based on the M06-2X calculations to investigate how to enhance the Hb···N hydrogen-bonded interaction. When the terminal hydrogen atoms(Ht) of B2H6 were replaced by X(X = Cl, Br, I) atoms, the Hb···N hydrogen bond will be strengthened. According to the electrostatic potentials in B2H2X4, two HF molecules were added to the interspace of the B-H-B-H four-membered ring of the B2H2X4···2NH3 complexes, and H···X hydrogen bond formed, resulting in further enhancing effect of Hb···N hydrogen bond. As a result, the positive cooperative effect of Hb···N hydrogen bond and H···X hydrogen bond do enhance the interactions of each other. The two measures not only enhance the strength of Hb···N hydrogen bond, but also achieve the goal to make the Hb···N hydrogen bond perpendicular to B···B direction.(2) The σ-hole of M2H6(M = Al, Ga, In) and π-hole of MH3(M = Al, Ga, In) were discovered and analyzed, the bimolecular complexes M2H6···NH3 and MH3···N2P2F4(M = Al, Ga, In) were constructed to carry out comparative studies on the group III σ-hole interactions and π-hole interactions. The two types of interactions are all partial-covalent interactions; the π-hole interactions are stronger than σ-hole interactions. The electrostatic energy is the largest contribution for forming the σ-hole and π-hole interaction, the polarization energy is also an important factor to form the M···N interaction. The electrostatic energy contributions to the interaction energy of the σ-hole interactions are somewhat greater than those of the π-hole interactions. However, the polarization contributions for the π-hole interactions are somewhat greater than those for the σ-hole interactions.(3)Through the molecular electrostatic potentials, electron localization function distribution, energy decomposition analyses and density difference of molecular formation(MFDD) analysis to investigate the nature of dative bond in XH3···YH3(X=B, Al, Ga, In; Y=N, P, As, Sb) complexes. We can naturally come to the conclusion that the contribution of the bonding atoms is not the same. In XH3···YH3(X=B, Al, Ga, In; Y=N, P, As, Sb) complexes, Y atoms makes up the largest part of the contribution in the X···Y bond, however, the X atoms also have some contribution. In this system, the electrostatic energy contributions to the interaction energy of the π-hole interactions are the largest, at the same time, rearrangement of electronic charge is also a important factors in forming dative bond.